Red LEDs to Grow Lettuce

Apparently red LEDs are 60 more efficient than

fluorescent light when growing vegetables hydroponically

According to IEEE Spectrum Online Of all the colors of the rainbow red is lettucersquos favorite

Chlorophyll the electrochemical engine of photosynthesis runs on red photons So if you are

growing the vegetable indoors in a factory why waste energy on colors you donrsquot need

Using a red LED-based growth process developed by Cosmo Plant Co in Fukuroi Japan

instead of a fluorescent lighting based one cuts a factoryrsquos electric bill by 60 percent the

company told Agence France Press

Cosmorsquos customers uses the technology to produce 7000 heads of lettuce per day all year round

in a 10-floor building on just 1000 square meters of space The lettuce matures more than three

times as fast under the LEDs than outdoors While growing lettuce in an open field is still less

costly growing it inside under LEDs means you donrsquot have to worry about crop-decimating

typhoons and other nasty weather

Would a Plant Grow Better Under a Green or Red Light

As indoor gardens soar in popularity so does the amount of misinformation about lighting techniques One persistent rumor is that plants grow better under green light however green light is not conducive for plant life Red light is the best light for plants to blossom

Instructions DifficultyEasy Misconceptions

1 Step 1 Perhaps what some people refer to as green lights are the new energy-efficient ie green LED lights There is a difference between the actual color or pigment of a light and the color of the light spectrum that is distinguished by its wavelength and frequency For example a standard HID light would produce a predominantly red light in the spectrum yet it shines as a normal white light This is not to be confused with encasing a light with a red translucent plastic which would produce a red-colored light According to the light spectrum blue or red light has the highest capacity to provide adequate lighting for growing plant life not a light that is colored green nor a green light in the spectrum chart

Types

1 Step 1 The main types of grow lights are LED compact fluorescent high-intensity-discharge (HID) metal halide and high-pressure sodium lamps LED lamps are the most energy efficient and produce the least heat (which can prevent the air conditioning from being unnecessarily used) HID are efficient in that they produce a high level of lumens per watt Fluorescent lights are full spectrum with blue as a prominent light HID are primarily red light and deficient in blue light

Size

1 Step 1 HID lamps are typically 24 inches by 12 inches and range from 250 watts to 1000 watts Compact fluorescent lamps are usually 14 inches by 4 inches LED lights are spotlights normally four to six inches in diameter

Effects

1 Step 1 Light in the red spectrum (not red-colored light) is most helpful for plants to bud and flower Light in the blue spectrum assists plants with vegetative growth

Considerations

1 Step 1 People generally use 25 percent blue light for most plant-growing purposes To expedite plant growth try 50 percent or 75 percent blue light Use 100 percent red light to maintain plants that are past their main growth state and to promote fruiting

Lettuce

Lettuce grown under LEDs harvested 32 days after planting seeds

TIP Use more blue light to produce sturdier seedlings For leaf crops switch to all red at the end of the growing cycle

Below Constant-yield lettuce garden One square foot is planted every four days 36 days from seed to harvest

Above Four types of lettuce grown in one square foot

LED Grow Lights

LED Grow Lights Ready for Prime Time

Letrsquos face it Everyone that uses high-intensity discharge (HID) garden lights has a

lovehate relationship with them

We love how Metal Halide (MH) or High Pressure Sodium (HPS) lights flood our gardenrsquos

canopy with intense light providing lots of energy for photosynthesis and keeping

internodal distances short We love how we can easily switch between them to match or

manipulate our plantsrsquo growth cycle We love how MH and HPS lights are widely available at reasonable prices

But we hate how much energy these lights consume in our area it costs at least $35 per

month to run a 600 watt MH or HPS light for 12 hours per day more in the summer due to

higher seasonal electric rates HID lights

are one of our most ldquoun-greenrdquo garden

tools with their high energy consumption

low efficiency ratings and mercury-

containing bulbs Critics rightly view them

as inconsistent with earth-friendly gardening methods

A big part of the problem is that HID lights

are inefficient A 400 watt HPS light is

only about 35 efficient which means

that only 35 of the electrical energy

delivered to the bulb is converted into

light with 65 converted into heat

Lighting ballasts are hot too contributing

to high levels of excess heat in most HID-illuminated garden rooms

This waste heat has to go somewhere so

we consume even more energy to cool

and vent gardens that use these lights Air

conditioning is often required and chillers

may be needed to keep nutrient solutions

from getting too hot

HID waste heat increases evaporation

from our reservoirs and growing media

and the transpiration rate of our plants Nutrient and water consumption go up as do the

required flow rates and reliability of our irrigation systems Just about every garden system

is significantly impacted by the waste heat from HID lights

What to do Itrsquos not like we can just turn off our grow lights and wait for something better

T5 fluorescent grow lights are energy efficient and cool running but their lower light output

makes them appropriate for plants that need less light such as leafy greens and foliage

plants At present only an HID garden light can put out enough light to provide a bountiful

harvest in plants that produce large fruit and flowers

The Promise of LED Grow Lights

Wersquove been waiting a long time for garden lights based on light-emitting diodes (LEDs) to

make it to ldquoprime timerdquo NASA and others have been experimenting with LED grow lights

since the mid-80rsquos and we are finally starting to see products reaching the market that reflect their findings These lights represent a major step forward

LED grow lights offer the dual benefit of low energy consumption and low heat generation

Some LED grow lights use so little electricity that they can be powered by a small solar

panel According to their manufacturers todayrsquos LED grow lights consume between 2 and

50 of the electricity used by the HID grow lights they reportedly replace Wersquove yet to see

in real-world application whether these lights will perform as well in the garden as those

ldquocomparablerdquo HIDs particularly for high-light crops

LEDs short for Light Emitting Diodes

are tiny semiconductor chips that

generate light when electrified It takes

a small amount of electricity to make

an LED glow (emit electrons) and the

elements that the diode is made from

determine the light spectrum it emits

An LED is backed by an internal

reflector and encased in an epoxy body

with an integrated lens Together

these components determine the angle

of the light emitted by the diode which

is shaped as a downward-facing cone

Individual LEDs produce relatively

small light cones so they are clustered

into arrays so the light cones overlap

increasing light intensity and coverage

area

LED grow lights are designed to

stimulate photosynthesis by providing light in the frequencies that plants primarily use for

this critical biological process Individual LEDs may contain one of 29 known combinations of

elements that emit light in different colors when excited by electrons Grow light

manufacturers emphasize blue and red LEDs in their fixtures sometimes with other colors

which gives many LED grow lights their distinctive purplish-red color Optimizing the light

spectrum helps in two ways it enhances photosynthesis and saves energy by not generating light in colors that plants do not use

LED Cost Savings

LED grow lights have a longer useful life

than MH or HPS lights as long as 15 years

for some fixtures and thus a lower ldquototal

cost of ownershiprdquo The total cost of

ownership includes the cost to buy the

light use it and replace expired bulbs

One manufacturer estimates that the total

cost of owning an LED grow light over five

years is about half the cost of a

comparable HPS light based on an

analysis that balances the upfront cost to

purchase an LED grow light against lower

electrical costs and eliminating the need

to periodically replace bulbs Their

analysis used an electric rate of $007 per

kilowatt hour ndash here in Southern California

where electric rates are twice as high the

total cost difference between an LED grow

light and a MH or HPS light would be even greater

You may also be able to save space or

move into a smaller space with LED grow

lights There is no need for bulky

reflectors and ventilationcooling

equipment such as fans air conditioners

and ductwork may be eliminated or scaled back The room will also be significantly quieter with fewer noisy fans ballasts and chillers

Thus the promise of LED grow lights has five aspects lower energy consumption lower

heat emissions customizable photosynthetic spectrum lower total cost of ownership and

smaller garden space requirements Can todayrsquos LED grow lights actually deliver these

benefits The answer to that question depends on who you ask Before we get to those

questions however letrsquos take a step back and examine light and photosynthesis a little more closely

Electromagnetic Spectrum and Photosynthesis

Electromagnetic radiation spans a broad range of wavelengths which includes what we

recognize as ldquovisible lightrdquo At the one end of the electromagnetic spectrum are gamma

rays which have a wavelength of 5-10 nanometers (nm) A nanometer is one-billionth of a

meter a very small measure indeed At the other end of the electromagnetic spectrum are

radio waves with a wavelength of 1012 nm Smack in the middle are the wavelengths that

can be seen by the human eye that fall between 380 and 750 nm This part of the

electromagnetic spectrum is what we call ldquovisible lightrdquo

Plants use visible light differently than we do Their leaves contain chlorophyll a compound

vital for photosynthesis the process by which plants convert light into fuel Chlorophyll

molecules are highly selective about the light they absorb blue light primarily in the 460-

480 nm range and red light around 640-680 nm Chlorophyll for the most part reflects

instead of absorbs most green and yellow light which is why plants appear green to our

eyes

Limiting any grow light to just red and blue light would lead to poor results since plants

also use most of rest of the visible spectrum though in lower amounts NASArsquos Biological

Sciences team at the Kennedy Space Center has done extensive research on this subject a

2006 paper published by the International Society of Horticultural Science documented

improvements in lettuce yields when 24 green light was added to LED grow lights that

otherwise produced only red and blue light Including light in the yellow-green spectrum

also helps to visually restore green color to plants making them look more ldquonormalrdquo and

makes it easier to identify garden problems such as nutrient deficiencies or pest attacks

This combination also makes it easier for gardeners to work in their gardens

Increasing the amount of red and blue light reaching the garden isnrsquot an idea limited to LED

grow lights Enhanced-spectrum MH and HPS bulbs such as Hortilux and SolarMax lamps

provide more blue and red light than standard bulbs So water-cooled HID lights according

to their manufacturers Enhanced-spectrum and water-cooled HID lights still put out a lot of

light in yellow-green wavelengths too that look bright to the human eye but donrsquot do much

for our plants An LED grow light designer isnrsquot trying to reproduce sunlight or make up for

the spectral shortcomings of a light originally designed for another purpose Instead they

are trying to create optimal light output for photosynthesis

Current state of the art

So do todayrsquos LED grow lights live up to expectations

Energy consumption is significantly lower for LED lights vs ldquoequivalentrdquo HID lights Most

grow light manufacturers are working to replace the light output of a 400-500 watt HID light

with between 30 and 300 watts of power consumed and some go quite a lot lower The

juryrsquos still out on how these lights truly compare to their HID cousins on garden performance and yield but on the energy promise they seem to perform well

The lights fare well on the heat promise too Most LED grow lights put out very little heat

so do not have any specific cooling requirements A lightrsquos heat output is affected by its

design some lights cluster LEDs in round or square ldquopodsrdquo or ldquorosettesrdquo that are spaced

along horizontal bars These designs help to limit heat accumulation by spacing the LEDs

farther apart Other lights bunch the LEDs close together in a single fixture to provide a

greater light intensity directly below the light These designs can accumulate heat so

generally incorporate heat management features such as heat shielding fans for air cooling

or water cooling

The third promise customized light spectrum is a topic where debates swirl Skeptics do

not believe LEDs can ever produce light that is intense enough to be effective for

photosynthesis no matter what color it is These concerns are based on earlier generation

LEDs that did not put out enough energy to work well as grow lights Todayrsquos ldquothird

generationrdquo LEDs reportedly solve this problem by putting out up to three watts of light

energy per LED a 20-50 fold improvement over second-generation LEDs New-generation

LEDs also have a wider ldquobeam anglerdquo that permits an LED to project light across a 120

degree arc instead of mostly just straight down (ldquopin pointrdquo lighting) This means wider light cones improving light intensity and coverage at the garden canopy

Passionate debates about LED grow light design and effectiveness are waged on a regular

basis in online gardening communities Some posts describe LED grow light trials people are

conducting in their homes While these posts are interesting reading and therersquos a lot to be

learned from them they should also be taken with a grain of salt Many hobbyists want to

debate whether LED grow lights are or can be effective The academic and scientific

communities satisfied for some time that LED grow lights are effective have moved on to

figuring out ldquohowrdquo

Updating Garden Methods for LEDs

One point that LED grow light manufacturers emphasize is that we must update our

gardening methods to use LED grow lights to their best advantage Using an LED grow light

without changing gardening methods will likely result in a disappointing outcome The first

caution is to not overwater Yoursquove eliminated one of the largest sources of heat in your

garden your HID garden lights

With less heat your plants consume less nutrient solution and less of it evaporates thus

less solution is needed One lighting manufacturer also suggests using a weaker nutrient

solution to match lower plant transpiration rates Less solution and less nutrients used this

should be good news right Yes and no Reservoirs can be smaller saving money and

space Fewer expensive bottles of hydroponic nutrient solutions are needed

The dark side is subtle but compelling the most

frequent cause of indoor plant death is

overwatering Itrsquos just as true for plants in a fully

automated indoor garden as it is for an African

violet on the kitchen windowsill Those accustomed

to gardening under HID lights will find that itrsquos

extremely easy to overwater under LED grow

lights Your plants simply need less water when there is less heat

Overwatering can lead to root rot or drowning if itrsquos

not caught and corrected right away When using

LED grow lights be sure to select a porous growing

media to provide adequate drainage and plenty of

air space in the root zone Also let your plants

almost dry more between feedings Overwatering

can also increase garden humidity levels which

can promote the development of fungus and other

garden ills Keep a close watch on growing media

moisture levels and garden relative humidity when

using LED grow lights An LED grow light that emits

some UV-A spectrum (invisible but felt as heat)

may help to kill or retard mildew Maintaining constant air movement within the garden

using oscillating or fixed fans will also help to keep mold and mildew in check

Grow light manufacturers also recommend supplementing the garden atmosphere with

carbon dioxide (CO2) While supplemental CO2 will improve the yield of any garden when

properly applied there are two particular benefits when using CO2 with LED grow lights

First even though an LED grow light may look dim to the human eye it is putting out a lot

of light energy in the spectrum needed for photosynthesis ndash ideally more than the plants

would receive under ldquocomparablerdquo MH or HPS lights Plants need higher CO2 levels in order

to turn this additional light into fuel The second benefit is that with lower heat output there

is less need to vent or air condition the garden space Itrsquos easier to seal the garden environment for CO2 when itrsquos not as hot

Top Two Concerns

We asked several LED lighting manufacturers about the concerns customers express when

considering an LED grow light Two primary concerns emerged

The first is the price for LED grow lights LED grow lights can be purchased on eBay for as

little as $9 for a screw-in replacement grow bulb to as much as $1500 for a water-cooled

garden light fixture reported to be equivalent to a 400- to 500 watt HPS light Donrsquot be

misled by the low price on some of the LED lights on eBay ndash they often include lower-

output inferior LEDs and some of them are recycled traffic signal lights A large number of

these inexpensive LED ldquogrow lightsrdquo may be needed to provide illumination for a standard-

sized hobby garden buyer beware A home gardener should expect to spend between $500

and $1500 for LED grow lights to illuminate a 3rsquo x 3rsquo growing space The ldquototal cost of

ownershiprdquo models discussed earlier are one way to understand the price issue LED grow

lights require a larger up-front investment which should be more than offset by reduced operating costs going forward

The second concern is that nobody

wants to go first More people are

interested in LED grow lights than are

ready to start using them Gardeners

do not want their crop to wind up as

the ldquoguinea pigrdquo in a failed garden

lighting experiment A lot of trials and

research have been conducted in

research laboratories that show LED

grow lights to be effective and cost-

efficient But those trials were done in

a laboratory setting Whatrsquos missing

are verifiable and repeatable

consumer-oriented trials that put LED

grow lights up against their HID

counterparts in conditions that

resemble a hobbyist indoor garden

room Until that happens individual

gardeners can experiment with LED grow lights on their own either on a small scale or by segregating a small number of plants within their garden for trials

Looking Ahead

What is the future of LED grow lights Near-term we should expect to see a wider variety of

LED grow lights coming onto the market These lights will increasingly include higher output

LEDs in a variety of light colors and configurations We expect to see combination lights

hitting the market using LED plus T5 fluorescent or HID garden lights to provide a more balanced spectrum than available from these garden lights used alone

We are starting to see LED grow lights designed to support different plant growth stages

such as grow and bloom and should expect lights to be introduced for specific plants such

as tomatoes herbs or orchids We will see continued improvements in light output

particularly as fourth-generation LEDs continue their migration from the lab to the market

Prices will begin to come down when sales volume increases

In the long run LED lighting could

obsolete almost every other type of

lighting Retrofit LED lamps that fit

into standard fluorescent lighting

fixtures are already available and

LED fixtures are in the works that

will replace street lights stadium

lights and other interior and

exterior lights Already Amsterdam

and Rotterdam in the Netherlands

are testing LED street lighting and

press reports indicate that other

major cities are considering similar trials

LED grow lights will be swept ahead

with the tide of mostly government-

funded research and development

currently underway Research

dollars invested by NASA and other

government agencies around the

globe are fueling tremendous

advances in LED lighting

technologies The energy saving

potential of LED lights is something

these entities cannot ignore if we

can find a way to consume less

energy to light up public and

private spaces we may be able to

postpone or scratch plans to build

new power plants or buy time until we are able to commercialize sustainable methods to generate and transport electricity

There is a lot of promise associated with LED grow lights but there are also unanswered

questions and unresolved debates The products that are available today should produce an

acceptable result so long as the gardener makes appropriate changes to their gardening

methods Wersquore looking forward to further articles and reports that describe how LED grow

lights perform against standard MH and HPS grow lights Wersquore hopeful about how LED grow

lights will fare in such comparisons

LED Growing Lights

Grow more plants with less electricity

Are LED growing lights better than fluorescent metal halide or high pressure sodium grow

lights Will they improve plant growth and will they use less electricity Is growing plants with LED growing lights environmentally friendly

Plants dont use the full visible spectrum to photosynthecize They predominantly use cool

(violet-blue and blue) and warm (orange-red) wavelengths which is a reflection of the

typical colors of natural night on a seasonal basis In the summer months when the sun is

more directly overhead cool colors predominate and tend to encourage healthy vegetative

growth while in spring and fall warm colors take over and tend to encourage flowering and fruiting

A typical metal halide grow light puts out much of its output in wavelength ranges that

plants do not use - cyan green yellow - and very little in the violet or blue regions So with

a metal halide grow light you are typically wasting much of the light shining down on your

plants A daylight metal halide light is more in the blue spectrum and so is useful for the

vegetative stage of growth but not for flowering or fruiting High pressure sodium lights

tend more to the warm red end of the spectrum and so are chiefly useful for flowering and fruiting

You can create your own LED growing lights by combining red and blue LED lights in roughly

a two- to-one proportion (two blue to one red) or buy an LED set designed specifically for

indoor growing which has blue and red LED grow lights in an appropriate proportion LED

grow lights have the benefit of low heat output so you dont need to worry about drying out

the soil or scorching the plants and they use very little electricity For example GlowPanel

LED growing lights cover a 15 square foot area (they are roughly 15 inches on a side) and

consume just 14 watts For growing purposes this light would be suitable for starting

seedlings or for growing herbs or lettuce indoors but is at the lower end of required light output for growing vegetables

Is it green to use LED growing lights Well its definitely an improvement to switch from

any of the other technologies as the amount of electricity youll use for the same amount of

growth is reduced significantly because of the concentration of light in the desired ranges of

the spectrum and because of the improved efficiency of LEDs But in absolute terms I

personally feel that LED growing lights should be used sparingly unless you have a source of carbon-neutral electricity that no one else has a use for

Why Lets consider a 6-square-foot herb garden using the GlowPanel LED growing lights

These lights consume 14 watts each for 15 square feet or 56 watts for the 6-square foot

garden The lights should be on about 12-16 hours a day for growing herbs or lettuce Lets

assume 12 hours to be conservative That meas were using 12 x 56 watts per day or 672 watt-hours Over a three month period that becomes about 60 kilowatt hours

Lets assume that 6-square foot garden produces 12 healthy heads of lettuce over the three

month period Each head of lettuce has therefore cost you 5 kilowatt hours of electricity

and might weigh a pound wet weight - and at about 95 water content would consist of less than an ounce of dried organic matter

Would a Plant Grow Better Under a Green or Red Light

As indoor gardens soar in popularity so does the amount of misinformation about lighting techniques One persistent rumor is that plants grow better under green light however green light is not conducive for plant life Red light is the best light for plants to blossom

Instructions DifficultyEasy Misconceptions

1 Step 1 Perhaps what some people refer to as green lights are the new energy-efficient ie green LED lights There is a difference between the actual color or pigment of a light and the color of the light spectrum that is distinguished by its wavelength and frequency For example a standard HID light would produce a predominantly red light in the spectrum yet it shines as a normal white light This is not to be confused with encasing a light with a red translucent plastic which would produce a red-colored light According to the light spectrum blue or red light has the highest capacity to provide adequate lighting for growing plant life not a light that is colored green nor a green light in the spectrum chart

Types

1 Step 1 The main types of grow lights are LED compact fluorescent high-intensity-discharge (HID) metal halide and high-pressure sodium lamps LED lamps are the most energy efficient and produce the least heat (which can prevent the air conditioning from being unnecessarily used) HID are efficient in that they produce a high level of lumens per watt Fluorescent lights are full spectrum with blue as a prominent light HID are primarily red light and deficient in blue light

Size

1 Step 1 HID lamps are typically 24 inches by 12 inches and range from 250 watts to 1000 watts Compact fluorescent lamps are usually 14 inches by 4 inches LED lights are spotlights normally four to six inches in diameter

Effects

1 Step 1 Light in the red spectrum (not red-colored light) is most helpful for plants to bud and flower Light in the blue spectrum assists plants with vegetative growth

Considerations

1 Step 1 People generally use 25 percent blue light for most plant-growing purposes To expedite plant growth try 50 percent or 75 percent blue light Use 100 percent red light to maintain plants that are past their main growth state and to promote fruiting

Lettuce

Lettuce grown under LEDs harvested 32 days after planting seeds

TIP Use more blue light to produce sturdier seedlings For leaf crops switch to all red at the end of the growing cycle

Below Constant-yield lettuce garden One square foot is planted every four days 36 days from seed to harvest

Above Four types of lettuce grown in one square foot

LED Grow Lights

LED Grow Lights Ready for Prime Time

Letrsquos face it Everyone that uses high-intensity discharge (HID) garden lights has a

lovehate relationship with them

We love how Metal Halide (MH) or High Pressure Sodium (HPS) lights flood our gardenrsquos

canopy with intense light providing lots of energy for photosynthesis and keeping

internodal distances short We love how we can easily switch between them to match or

manipulate our plantsrsquo growth cycle We love how MH and HPS lights are widely available at reasonable prices

But we hate how much energy these lights consume in our area it costs at least $35 per

month to run a 600 watt MH or HPS light for 12 hours per day more in the summer due to

higher seasonal electric rates HID lights

are one of our most ldquoun-greenrdquo garden

tools with their high energy consumption

low efficiency ratings and mercury-

containing bulbs Critics rightly view them

as inconsistent with earth-friendly gardening methods

A big part of the problem is that HID lights

are inefficient A 400 watt HPS light is

only about 35 efficient which means

that only 35 of the electrical energy

delivered to the bulb is converted into

light with 65 converted into heat

Lighting ballasts are hot too contributing

to high levels of excess heat in most HID-illuminated garden rooms

This waste heat has to go somewhere so

we consume even more energy to cool

and vent gardens that use these lights Air

conditioning is often required and chillers

may be needed to keep nutrient solutions

from getting too hot

HID waste heat increases evaporation

from our reservoirs and growing media

and the transpiration rate of our plants Nutrient and water consumption go up as do the

required flow rates and reliability of our irrigation systems Just about every garden system

is significantly impacted by the waste heat from HID lights

What to do Itrsquos not like we can just turn off our grow lights and wait for something better

T5 fluorescent grow lights are energy efficient and cool running but their lower light output

makes them appropriate for plants that need less light such as leafy greens and foliage

plants At present only an HID garden light can put out enough light to provide a bountiful

harvest in plants that produce large fruit and flowers

The Promise of LED Grow Lights

Wersquove been waiting a long time for garden lights based on light-emitting diodes (LEDs) to

make it to ldquoprime timerdquo NASA and others have been experimenting with LED grow lights

since the mid-80rsquos and we are finally starting to see products reaching the market that reflect their findings These lights represent a major step forward

LED grow lights offer the dual benefit of low energy consumption and low heat generation

Some LED grow lights use so little electricity that they can be powered by a small solar

panel According to their manufacturers todayrsquos LED grow lights consume between 2 and

50 of the electricity used by the HID grow lights they reportedly replace Wersquove yet to see

in real-world application whether these lights will perform as well in the garden as those

ldquocomparablerdquo HIDs particularly for high-light crops

LEDs short for Light Emitting Diodes

are tiny semiconductor chips that

generate light when electrified It takes

a small amount of electricity to make

an LED glow (emit electrons) and the

elements that the diode is made from

determine the light spectrum it emits

An LED is backed by an internal

reflector and encased in an epoxy body

with an integrated lens Together

these components determine the angle

of the light emitted by the diode which

is shaped as a downward-facing cone

Individual LEDs produce relatively

small light cones so they are clustered

into arrays so the light cones overlap

increasing light intensity and coverage

area

LED grow lights are designed to

stimulate photosynthesis by providing light in the frequencies that plants primarily use for

this critical biological process Individual LEDs may contain one of 29 known combinations of

elements that emit light in different colors when excited by electrons Grow light

manufacturers emphasize blue and red LEDs in their fixtures sometimes with other colors

which gives many LED grow lights their distinctive purplish-red color Optimizing the light

spectrum helps in two ways it enhances photosynthesis and saves energy by not generating light in colors that plants do not use

LED Cost Savings

LED grow lights have a longer useful life

than MH or HPS lights as long as 15 years

for some fixtures and thus a lower ldquototal

cost of ownershiprdquo The total cost of

ownership includes the cost to buy the

light use it and replace expired bulbs

One manufacturer estimates that the total

cost of owning an LED grow light over five

years is about half the cost of a

comparable HPS light based on an

analysis that balances the upfront cost to

purchase an LED grow light against lower

electrical costs and eliminating the need

to periodically replace bulbs Their

analysis used an electric rate of $007 per

kilowatt hour ndash here in Southern California

where electric rates are twice as high the

total cost difference between an LED grow

light and a MH or HPS light would be even greater

You may also be able to save space or

move into a smaller space with LED grow

lights There is no need for bulky

reflectors and ventilationcooling

equipment such as fans air conditioners

and ductwork may be eliminated or scaled back The room will also be significantly quieter with fewer noisy fans ballasts and chillers

Thus the promise of LED grow lights has five aspects lower energy consumption lower

heat emissions customizable photosynthetic spectrum lower total cost of ownership and

smaller garden space requirements Can todayrsquos LED grow lights actually deliver these

benefits The answer to that question depends on who you ask Before we get to those

questions however letrsquos take a step back and examine light and photosynthesis a little more closely

Electromagnetic Spectrum and Photosynthesis

Electromagnetic radiation spans a broad range of wavelengths which includes what we

recognize as ldquovisible lightrdquo At the one end of the electromagnetic spectrum are gamma

rays which have a wavelength of 5-10 nanometers (nm) A nanometer is one-billionth of a

meter a very small measure indeed At the other end of the electromagnetic spectrum are

radio waves with a wavelength of 1012 nm Smack in the middle are the wavelengths that

can be seen by the human eye that fall between 380 and 750 nm This part of the

electromagnetic spectrum is what we call ldquovisible lightrdquo

Plants use visible light differently than we do Their leaves contain chlorophyll a compound

vital for photosynthesis the process by which plants convert light into fuel Chlorophyll

molecules are highly selective about the light they absorb blue light primarily in the 460-

480 nm range and red light around 640-680 nm Chlorophyll for the most part reflects

instead of absorbs most green and yellow light which is why plants appear green to our

eyes

Limiting any grow light to just red and blue light would lead to poor results since plants

also use most of rest of the visible spectrum though in lower amounts NASArsquos Biological

Sciences team at the Kennedy Space Center has done extensive research on this subject a

2006 paper published by the International Society of Horticultural Science documented

improvements in lettuce yields when 24 green light was added to LED grow lights that

otherwise produced only red and blue light Including light in the yellow-green spectrum

also helps to visually restore green color to plants making them look more ldquonormalrdquo and

makes it easier to identify garden problems such as nutrient deficiencies or pest attacks

This combination also makes it easier for gardeners to work in their gardens

Increasing the amount of red and blue light reaching the garden isnrsquot an idea limited to LED

grow lights Enhanced-spectrum MH and HPS bulbs such as Hortilux and SolarMax lamps

provide more blue and red light than standard bulbs So water-cooled HID lights according

to their manufacturers Enhanced-spectrum and water-cooled HID lights still put out a lot of

light in yellow-green wavelengths too that look bright to the human eye but donrsquot do much

for our plants An LED grow light designer isnrsquot trying to reproduce sunlight or make up for

the spectral shortcomings of a light originally designed for another purpose Instead they

are trying to create optimal light output for photosynthesis

Current state of the art

So do todayrsquos LED grow lights live up to expectations

Energy consumption is significantly lower for LED lights vs ldquoequivalentrdquo HID lights Most

grow light manufacturers are working to replace the light output of a 400-500 watt HID light

with between 30 and 300 watts of power consumed and some go quite a lot lower The

juryrsquos still out on how these lights truly compare to their HID cousins on garden performance and yield but on the energy promise they seem to perform well

The lights fare well on the heat promise too Most LED grow lights put out very little heat

so do not have any specific cooling requirements A lightrsquos heat output is affected by its

design some lights cluster LEDs in round or square ldquopodsrdquo or ldquorosettesrdquo that are spaced

along horizontal bars These designs help to limit heat accumulation by spacing the LEDs

farther apart Other lights bunch the LEDs close together in a single fixture to provide a

greater light intensity directly below the light These designs can accumulate heat so

generally incorporate heat management features such as heat shielding fans for air cooling

or water cooling

The third promise customized light spectrum is a topic where debates swirl Skeptics do

not believe LEDs can ever produce light that is intense enough to be effective for

photosynthesis no matter what color it is These concerns are based on earlier generation

LEDs that did not put out enough energy to work well as grow lights Todayrsquos ldquothird

generationrdquo LEDs reportedly solve this problem by putting out up to three watts of light

energy per LED a 20-50 fold improvement over second-generation LEDs New-generation

LEDs also have a wider ldquobeam anglerdquo that permits an LED to project light across a 120

degree arc instead of mostly just straight down (ldquopin pointrdquo lighting) This means wider light cones improving light intensity and coverage at the garden canopy

Passionate debates about LED grow light design and effectiveness are waged on a regular

basis in online gardening communities Some posts describe LED grow light trials people are

conducting in their homes While these posts are interesting reading and therersquos a lot to be

learned from them they should also be taken with a grain of salt Many hobbyists want to

debate whether LED grow lights are or can be effective The academic and scientific

communities satisfied for some time that LED grow lights are effective have moved on to

figuring out ldquohowrdquo

Updating Garden Methods for LEDs

One point that LED grow light manufacturers emphasize is that we must update our

gardening methods to use LED grow lights to their best advantage Using an LED grow light

without changing gardening methods will likely result in a disappointing outcome The first

caution is to not overwater Yoursquove eliminated one of the largest sources of heat in your

garden your HID garden lights

With less heat your plants consume less nutrient solution and less of it evaporates thus

less solution is needed One lighting manufacturer also suggests using a weaker nutrient

solution to match lower plant transpiration rates Less solution and less nutrients used this

should be good news right Yes and no Reservoirs can be smaller saving money and

space Fewer expensive bottles of hydroponic nutrient solutions are needed

The dark side is subtle but compelling the most

frequent cause of indoor plant death is

overwatering Itrsquos just as true for plants in a fully

automated indoor garden as it is for an African

violet on the kitchen windowsill Those accustomed

to gardening under HID lights will find that itrsquos

extremely easy to overwater under LED grow

lights Your plants simply need less water when there is less heat

Overwatering can lead to root rot or drowning if itrsquos

not caught and corrected right away When using

LED grow lights be sure to select a porous growing

media to provide adequate drainage and plenty of

air space in the root zone Also let your plants

almost dry more between feedings Overwatering

can also increase garden humidity levels which

can promote the development of fungus and other

garden ills Keep a close watch on growing media

moisture levels and garden relative humidity when

using LED grow lights An LED grow light that emits

some UV-A spectrum (invisible but felt as heat)

may help to kill or retard mildew Maintaining constant air movement within the garden

using oscillating or fixed fans will also help to keep mold and mildew in check

Grow light manufacturers also recommend supplementing the garden atmosphere with

carbon dioxide (CO2) While supplemental CO2 will improve the yield of any garden when

properly applied there are two particular benefits when using CO2 with LED grow lights

First even though an LED grow light may look dim to the human eye it is putting out a lot

of light energy in the spectrum needed for photosynthesis ndash ideally more than the plants

would receive under ldquocomparablerdquo MH or HPS lights Plants need higher CO2 levels in order

to turn this additional light into fuel The second benefit is that with lower heat output there

is less need to vent or air condition the garden space Itrsquos easier to seal the garden environment for CO2 when itrsquos not as hot

Top Two Concerns

We asked several LED lighting manufacturers about the concerns customers express when

considering an LED grow light Two primary concerns emerged

The first is the price for LED grow lights LED grow lights can be purchased on eBay for as

little as $9 for a screw-in replacement grow bulb to as much as $1500 for a water-cooled

garden light fixture reported to be equivalent to a 400- to 500 watt HPS light Donrsquot be

misled by the low price on some of the LED lights on eBay ndash they often include lower-

output inferior LEDs and some of them are recycled traffic signal lights A large number of

these inexpensive LED ldquogrow lightsrdquo may be needed to provide illumination for a standard-

sized hobby garden buyer beware A home gardener should expect to spend between $500

and $1500 for LED grow lights to illuminate a 3rsquo x 3rsquo growing space The ldquototal cost of

ownershiprdquo models discussed earlier are one way to understand the price issue LED grow

lights require a larger up-front investment which should be more than offset by reduced operating costs going forward

The second concern is that nobody

wants to go first More people are

interested in LED grow lights than are

ready to start using them Gardeners

do not want their crop to wind up as

the ldquoguinea pigrdquo in a failed garden

lighting experiment A lot of trials and

research have been conducted in

research laboratories that show LED

grow lights to be effective and cost-

efficient But those trials were done in

a laboratory setting Whatrsquos missing

are verifiable and repeatable

consumer-oriented trials that put LED

grow lights up against their HID

counterparts in conditions that

resemble a hobbyist indoor garden

room Until that happens individual

gardeners can experiment with LED grow lights on their own either on a small scale or by segregating a small number of plants within their garden for trials

Looking Ahead

What is the future of LED grow lights Near-term we should expect to see a wider variety of

LED grow lights coming onto the market These lights will increasingly include higher output

LEDs in a variety of light colors and configurations We expect to see combination lights

hitting the market using LED plus T5 fluorescent or HID garden lights to provide a more balanced spectrum than available from these garden lights used alone

We are starting to see LED grow lights designed to support different plant growth stages

such as grow and bloom and should expect lights to be introduced for specific plants such

as tomatoes herbs or orchids We will see continued improvements in light output

particularly as fourth-generation LEDs continue their migration from the lab to the market

Prices will begin to come down when sales volume increases

In the long run LED lighting could

obsolete almost every other type of

lighting Retrofit LED lamps that fit

into standard fluorescent lighting

fixtures are already available and

LED fixtures are in the works that

will replace street lights stadium

lights and other interior and

exterior lights Already Amsterdam

and Rotterdam in the Netherlands

are testing LED street lighting and

press reports indicate that other

major cities are considering similar trials

LED grow lights will be swept ahead

with the tide of mostly government-

funded research and development

currently underway Research

dollars invested by NASA and other

government agencies around the

globe are fueling tremendous

advances in LED lighting

technologies The energy saving

potential of LED lights is something

these entities cannot ignore if we

can find a way to consume less

energy to light up public and

private spaces we may be able to

postpone or scratch plans to build

new power plants or buy time until we are able to commercialize sustainable methods to generate and transport electricity

There is a lot of promise associated with LED grow lights but there are also unanswered

questions and unresolved debates The products that are available today should produce an

acceptable result so long as the gardener makes appropriate changes to their gardening

methods Wersquore looking forward to further articles and reports that describe how LED grow

lights perform against standard MH and HPS grow lights Wersquore hopeful about how LED grow

lights will fare in such comparisons

LED Growing Lights

Grow more plants with less electricity

Are LED growing lights better than fluorescent metal halide or high pressure sodium grow

lights Will they improve plant growth and will they use less electricity Is growing plants with LED growing lights environmentally friendly

Plants dont use the full visible spectrum to photosynthecize They predominantly use cool

(violet-blue and blue) and warm (orange-red) wavelengths which is a reflection of the

typical colors of natural night on a seasonal basis In the summer months when the sun is

more directly overhead cool colors predominate and tend to encourage healthy vegetative

growth while in spring and fall warm colors take over and tend to encourage flowering and fruiting

A typical metal halide grow light puts out much of its output in wavelength ranges that

plants do not use - cyan green yellow - and very little in the violet or blue regions So with

a metal halide grow light you are typically wasting much of the light shining down on your

plants A daylight metal halide light is more in the blue spectrum and so is useful for the

vegetative stage of growth but not for flowering or fruiting High pressure sodium lights

tend more to the warm red end of the spectrum and so are chiefly useful for flowering and fruiting

You can create your own LED growing lights by combining red and blue LED lights in roughly

a two- to-one proportion (two blue to one red) or buy an LED set designed specifically for

indoor growing which has blue and red LED grow lights in an appropriate proportion LED

grow lights have the benefit of low heat output so you dont need to worry about drying out

the soil or scorching the plants and they use very little electricity For example GlowPanel

LED growing lights cover a 15 square foot area (they are roughly 15 inches on a side) and

consume just 14 watts For growing purposes this light would be suitable for starting

seedlings or for growing herbs or lettuce indoors but is at the lower end of required light output for growing vegetables

Is it green to use LED growing lights Well its definitely an improvement to switch from

any of the other technologies as the amount of electricity youll use for the same amount of

growth is reduced significantly because of the concentration of light in the desired ranges of

the spectrum and because of the improved efficiency of LEDs But in absolute terms I

personally feel that LED growing lights should be used sparingly unless you have a source of carbon-neutral electricity that no one else has a use for

Why Lets consider a 6-square-foot herb garden using the GlowPanel LED growing lights

These lights consume 14 watts each for 15 square feet or 56 watts for the 6-square foot

garden The lights should be on about 12-16 hours a day for growing herbs or lettuce Lets

assume 12 hours to be conservative That meas were using 12 x 56 watts per day or 672 watt-hours Over a three month period that becomes about 60 kilowatt hours

Lets assume that 6-square foot garden produces 12 healthy heads of lettuce over the three

month period Each head of lettuce has therefore cost you 5 kilowatt hours of electricity

and might weigh a pound wet weight - and at about 95 water content would consist of less than an ounce of dried organic matter

Considerations

1 Step 1 People generally use 25 percent blue light for most plant-growing purposes To expedite plant growth try 50 percent or 75 percent blue light Use 100 percent red light to maintain plants that are past their main growth state and to promote fruiting

Lettuce

Lettuce grown under LEDs harvested 32 days after planting seeds

TIP Use more blue light to produce sturdier seedlings For leaf crops switch to all red at the end of the growing cycle

Below Constant-yield lettuce garden One square foot is planted every four days 36 days from seed to harvest

Above Four types of lettuce grown in one square foot

LED Grow Lights

LED Grow Lights Ready for Prime Time

Letrsquos face it Everyone that uses high-intensity discharge (HID) garden lights has a

lovehate relationship with them

We love how Metal Halide (MH) or High Pressure Sodium (HPS) lights flood our gardenrsquos

canopy with intense light providing lots of energy for photosynthesis and keeping

internodal distances short We love how we can easily switch between them to match or

manipulate our plantsrsquo growth cycle We love how MH and HPS lights are widely available at reasonable prices

But we hate how much energy these lights consume in our area it costs at least $35 per

month to run a 600 watt MH or HPS light for 12 hours per day more in the summer due to

higher seasonal electric rates HID lights

are one of our most ldquoun-greenrdquo garden

tools with their high energy consumption

low efficiency ratings and mercury-

containing bulbs Critics rightly view them

as inconsistent with earth-friendly gardening methods

A big part of the problem is that HID lights

are inefficient A 400 watt HPS light is

only about 35 efficient which means

that only 35 of the electrical energy

delivered to the bulb is converted into

light with 65 converted into heat

Lighting ballasts are hot too contributing

to high levels of excess heat in most HID-illuminated garden rooms

This waste heat has to go somewhere so

we consume even more energy to cool

and vent gardens that use these lights Air

conditioning is often required and chillers

may be needed to keep nutrient solutions

from getting too hot

HID waste heat increases evaporation

from our reservoirs and growing media

and the transpiration rate of our plants Nutrient and water consumption go up as do the

required flow rates and reliability of our irrigation systems Just about every garden system

is significantly impacted by the waste heat from HID lights

What to do Itrsquos not like we can just turn off our grow lights and wait for something better

T5 fluorescent grow lights are energy efficient and cool running but their lower light output

makes them appropriate for plants that need less light such as leafy greens and foliage

plants At present only an HID garden light can put out enough light to provide a bountiful

harvest in plants that produce large fruit and flowers

The Promise of LED Grow Lights

Wersquove been waiting a long time for garden lights based on light-emitting diodes (LEDs) to

make it to ldquoprime timerdquo NASA and others have been experimenting with LED grow lights

since the mid-80rsquos and we are finally starting to see products reaching the market that reflect their findings These lights represent a major step forward

LED grow lights offer the dual benefit of low energy consumption and low heat generation

Some LED grow lights use so little electricity that they can be powered by a small solar

panel According to their manufacturers todayrsquos LED grow lights consume between 2 and

50 of the electricity used by the HID grow lights they reportedly replace Wersquove yet to see

in real-world application whether these lights will perform as well in the garden as those

ldquocomparablerdquo HIDs particularly for high-light crops

LEDs short for Light Emitting Diodes

are tiny semiconductor chips that

generate light when electrified It takes

a small amount of electricity to make

an LED glow (emit electrons) and the

elements that the diode is made from

determine the light spectrum it emits

An LED is backed by an internal

reflector and encased in an epoxy body

with an integrated lens Together

these components determine the angle

of the light emitted by the diode which

is shaped as a downward-facing cone

Individual LEDs produce relatively

small light cones so they are clustered

into arrays so the light cones overlap

increasing light intensity and coverage

area

LED grow lights are designed to

stimulate photosynthesis by providing light in the frequencies that plants primarily use for

this critical biological process Individual LEDs may contain one of 29 known combinations of

elements that emit light in different colors when excited by electrons Grow light

manufacturers emphasize blue and red LEDs in their fixtures sometimes with other colors

which gives many LED grow lights their distinctive purplish-red color Optimizing the light

spectrum helps in two ways it enhances photosynthesis and saves energy by not generating light in colors that plants do not use

LED Cost Savings

LED grow lights have a longer useful life

than MH or HPS lights as long as 15 years

for some fixtures and thus a lower ldquototal

cost of ownershiprdquo The total cost of

ownership includes the cost to buy the

light use it and replace expired bulbs

One manufacturer estimates that the total

cost of owning an LED grow light over five

years is about half the cost of a

comparable HPS light based on an

analysis that balances the upfront cost to

purchase an LED grow light against lower

electrical costs and eliminating the need

to periodically replace bulbs Their

analysis used an electric rate of $007 per

kilowatt hour ndash here in Southern California

where electric rates are twice as high the

total cost difference between an LED grow

light and a MH or HPS light would be even greater

You may also be able to save space or

move into a smaller space with LED grow

lights There is no need for bulky

reflectors and ventilationcooling

equipment such as fans air conditioners

and ductwork may be eliminated or scaled back The room will also be significantly quieter with fewer noisy fans ballasts and chillers

Thus the promise of LED grow lights has five aspects lower energy consumption lower

heat emissions customizable photosynthetic spectrum lower total cost of ownership and

smaller garden space requirements Can todayrsquos LED grow lights actually deliver these

benefits The answer to that question depends on who you ask Before we get to those

questions however letrsquos take a step back and examine light and photosynthesis a little more closely

Electromagnetic Spectrum and Photosynthesis

Electromagnetic radiation spans a broad range of wavelengths which includes what we

recognize as ldquovisible lightrdquo At the one end of the electromagnetic spectrum are gamma

rays which have a wavelength of 5-10 nanometers (nm) A nanometer is one-billionth of a

meter a very small measure indeed At the other end of the electromagnetic spectrum are

radio waves with a wavelength of 1012 nm Smack in the middle are the wavelengths that

can be seen by the human eye that fall between 380 and 750 nm This part of the

electromagnetic spectrum is what we call ldquovisible lightrdquo

Plants use visible light differently than we do Their leaves contain chlorophyll a compound

vital for photosynthesis the process by which plants convert light into fuel Chlorophyll

molecules are highly selective about the light they absorb blue light primarily in the 460-

480 nm range and red light around 640-680 nm Chlorophyll for the most part reflects

instead of absorbs most green and yellow light which is why plants appear green to our

eyes

Limiting any grow light to just red and blue light would lead to poor results since plants

also use most of rest of the visible spectrum though in lower amounts NASArsquos Biological

Sciences team at the Kennedy Space Center has done extensive research on this subject a

2006 paper published by the International Society of Horticultural Science documented

improvements in lettuce yields when 24 green light was added to LED grow lights that

otherwise produced only red and blue light Including light in the yellow-green spectrum

also helps to visually restore green color to plants making them look more ldquonormalrdquo and

makes it easier to identify garden problems such as nutrient deficiencies or pest attacks

This combination also makes it easier for gardeners to work in their gardens

Increasing the amount of red and blue light reaching the garden isnrsquot an idea limited to LED

grow lights Enhanced-spectrum MH and HPS bulbs such as Hortilux and SolarMax lamps

provide more blue and red light than standard bulbs So water-cooled HID lights according

to their manufacturers Enhanced-spectrum and water-cooled HID lights still put out a lot of

light in yellow-green wavelengths too that look bright to the human eye but donrsquot do much

for our plants An LED grow light designer isnrsquot trying to reproduce sunlight or make up for

the spectral shortcomings of a light originally designed for another purpose Instead they

are trying to create optimal light output for photosynthesis

Current state of the art

So do todayrsquos LED grow lights live up to expectations

Energy consumption is significantly lower for LED lights vs ldquoequivalentrdquo HID lights Most

grow light manufacturers are working to replace the light output of a 400-500 watt HID light

with between 30 and 300 watts of power consumed and some go quite a lot lower The

juryrsquos still out on how these lights truly compare to their HID cousins on garden performance and yield but on the energy promise they seem to perform well

The lights fare well on the heat promise too Most LED grow lights put out very little heat

so do not have any specific cooling requirements A lightrsquos heat output is affected by its

design some lights cluster LEDs in round or square ldquopodsrdquo or ldquorosettesrdquo that are spaced

along horizontal bars These designs help to limit heat accumulation by spacing the LEDs

farther apart Other lights bunch the LEDs close together in a single fixture to provide a

greater light intensity directly below the light These designs can accumulate heat so

generally incorporate heat management features such as heat shielding fans for air cooling

or water cooling

The third promise customized light spectrum is a topic where debates swirl Skeptics do

not believe LEDs can ever produce light that is intense enough to be effective for

photosynthesis no matter what color it is These concerns are based on earlier generation

LEDs that did not put out enough energy to work well as grow lights Todayrsquos ldquothird

generationrdquo LEDs reportedly solve this problem by putting out up to three watts of light

energy per LED a 20-50 fold improvement over second-generation LEDs New-generation

LEDs also have a wider ldquobeam anglerdquo that permits an LED to project light across a 120

degree arc instead of mostly just straight down (ldquopin pointrdquo lighting) This means wider light cones improving light intensity and coverage at the garden canopy

Passionate debates about LED grow light design and effectiveness are waged on a regular

basis in online gardening communities Some posts describe LED grow light trials people are

conducting in their homes While these posts are interesting reading and therersquos a lot to be

learned from them they should also be taken with a grain of salt Many hobbyists want to

debate whether LED grow lights are or can be effective The academic and scientific

communities satisfied for some time that LED grow lights are effective have moved on to

figuring out ldquohowrdquo

Updating Garden Methods for LEDs

One point that LED grow light manufacturers emphasize is that we must update our

gardening methods to use LED grow lights to their best advantage Using an LED grow light

without changing gardening methods will likely result in a disappointing outcome The first

caution is to not overwater Yoursquove eliminated one of the largest sources of heat in your

garden your HID garden lights

With less heat your plants consume less nutrient solution and less of it evaporates thus

less solution is needed One lighting manufacturer also suggests using a weaker nutrient

solution to match lower plant transpiration rates Less solution and less nutrients used this

should be good news right Yes and no Reservoirs can be smaller saving money and

space Fewer expensive bottles of hydroponic nutrient solutions are needed

The dark side is subtle but compelling the most

frequent cause of indoor plant death is

overwatering Itrsquos just as true for plants in a fully

automated indoor garden as it is for an African

violet on the kitchen windowsill Those accustomed

to gardening under HID lights will find that itrsquos

extremely easy to overwater under LED grow

lights Your plants simply need less water when there is less heat

Overwatering can lead to root rot or drowning if itrsquos

not caught and corrected right away When using

LED grow lights be sure to select a porous growing

media to provide adequate drainage and plenty of

air space in the root zone Also let your plants

almost dry more between feedings Overwatering

can also increase garden humidity levels which

can promote the development of fungus and other

garden ills Keep a close watch on growing media

moisture levels and garden relative humidity when

using LED grow lights An LED grow light that emits

some UV-A spectrum (invisible but felt as heat)

may help to kill or retard mildew Maintaining constant air movement within the garden

using oscillating or fixed fans will also help to keep mold and mildew in check

Grow light manufacturers also recommend supplementing the garden atmosphere with

carbon dioxide (CO2) While supplemental CO2 will improve the yield of any garden when

properly applied there are two particular benefits when using CO2 with LED grow lights

First even though an LED grow light may look dim to the human eye it is putting out a lot

of light energy in the spectrum needed for photosynthesis ndash ideally more than the plants

would receive under ldquocomparablerdquo MH or HPS lights Plants need higher CO2 levels in order

to turn this additional light into fuel The second benefit is that with lower heat output there

is less need to vent or air condition the garden space Itrsquos easier to seal the garden environment for CO2 when itrsquos not as hot

Top Two Concerns

We asked several LED lighting manufacturers about the concerns customers express when

considering an LED grow light Two primary concerns emerged

The first is the price for LED grow lights LED grow lights can be purchased on eBay for as

little as $9 for a screw-in replacement grow bulb to as much as $1500 for a water-cooled

garden light fixture reported to be equivalent to a 400- to 500 watt HPS light Donrsquot be

misled by the low price on some of the LED lights on eBay ndash they often include lower-

output inferior LEDs and some of them are recycled traffic signal lights A large number of

these inexpensive LED ldquogrow lightsrdquo may be needed to provide illumination for a standard-

sized hobby garden buyer beware A home gardener should expect to spend between $500

and $1500 for LED grow lights to illuminate a 3rsquo x 3rsquo growing space The ldquototal cost of

ownershiprdquo models discussed earlier are one way to understand the price issue LED grow

lights require a larger up-front investment which should be more than offset by reduced operating costs going forward

The second concern is that nobody

wants to go first More people are

interested in LED grow lights than are

ready to start using them Gardeners

do not want their crop to wind up as

the ldquoguinea pigrdquo in a failed garden

lighting experiment A lot of trials and

research have been conducted in

research laboratories that show LED

grow lights to be effective and cost-

efficient But those trials were done in

a laboratory setting Whatrsquos missing

are verifiable and repeatable

consumer-oriented trials that put LED

grow lights up against their HID

counterparts in conditions that

resemble a hobbyist indoor garden

room Until that happens individual

gardeners can experiment with LED grow lights on their own either on a small scale or by segregating a small number of plants within their garden for trials

Looking Ahead

What is the future of LED grow lights Near-term we should expect to see a wider variety of

LED grow lights coming onto the market These lights will increasingly include higher output

LEDs in a variety of light colors and configurations We expect to see combination lights

hitting the market using LED plus T5 fluorescent or HID garden lights to provide a more balanced spectrum than available from these garden lights used alone

We are starting to see LED grow lights designed to support different plant growth stages

such as grow and bloom and should expect lights to be introduced for specific plants such

as tomatoes herbs or orchids We will see continued improvements in light output

particularly as fourth-generation LEDs continue their migration from the lab to the market

Prices will begin to come down when sales volume increases

In the long run LED lighting could

obsolete almost every other type of

lighting Retrofit LED lamps that fit

into standard fluorescent lighting

fixtures are already available and

LED fixtures are in the works that

will replace street lights stadium

lights and other interior and

exterior lights Already Amsterdam

and Rotterdam in the Netherlands

are testing LED street lighting and

press reports indicate that other

major cities are considering similar trials

LED grow lights will be swept ahead

with the tide of mostly government-

funded research and development

currently underway Research

dollars invested by NASA and other

government agencies around the

globe are fueling tremendous

advances in LED lighting

technologies The energy saving

potential of LED lights is something

these entities cannot ignore if we

can find a way to consume less

energy to light up public and

private spaces we may be able to

postpone or scratch plans to build

new power plants or buy time until we are able to commercialize sustainable methods to generate and transport electricity

There is a lot of promise associated with LED grow lights but there are also unanswered

questions and unresolved debates The products that are available today should produce an

acceptable result so long as the gardener makes appropriate changes to their gardening

methods Wersquore looking forward to further articles and reports that describe how LED grow

lights perform against standard MH and HPS grow lights Wersquore hopeful about how LED grow

lights will fare in such comparisons

LED Growing Lights

Grow more plants with less electricity

Are LED growing lights better than fluorescent metal halide or high pressure sodium grow

lights Will they improve plant growth and will they use less electricity Is growing plants with LED growing lights environmentally friendly

Plants dont use the full visible spectrum to photosynthecize They predominantly use cool

(violet-blue and blue) and warm (orange-red) wavelengths which is a reflection of the

typical colors of natural night on a seasonal basis In the summer months when the sun is

more directly overhead cool colors predominate and tend to encourage healthy vegetative

growth while in spring and fall warm colors take over and tend to encourage flowering and fruiting

A typical metal halide grow light puts out much of its output in wavelength ranges that

plants do not use - cyan green yellow - and very little in the violet or blue regions So with

a metal halide grow light you are typically wasting much of the light shining down on your

plants A daylight metal halide light is more in the blue spectrum and so is useful for the

vegetative stage of growth but not for flowering or fruiting High pressure sodium lights

tend more to the warm red end of the spectrum and so are chiefly useful for flowering and fruiting

You can create your own LED growing lights by combining red and blue LED lights in roughly

a two- to-one proportion (two blue to one red) or buy an LED set designed specifically for

indoor growing which has blue and red LED grow lights in an appropriate proportion LED

grow lights have the benefit of low heat output so you dont need to worry about drying out

the soil or scorching the plants and they use very little electricity For example GlowPanel

LED growing lights cover a 15 square foot area (they are roughly 15 inches on a side) and

consume just 14 watts For growing purposes this light would be suitable for starting

seedlings or for growing herbs or lettuce indoors but is at the lower end of required light output for growing vegetables

Is it green to use LED growing lights Well its definitely an improvement to switch from

any of the other technologies as the amount of electricity youll use for the same amount of

growth is reduced significantly because of the concentration of light in the desired ranges of

the spectrum and because of the improved efficiency of LEDs But in absolute terms I

personally feel that LED growing lights should be used sparingly unless you have a source of carbon-neutral electricity that no one else has a use for

Why Lets consider a 6-square-foot herb garden using the GlowPanel LED growing lights

These lights consume 14 watts each for 15 square feet or 56 watts for the 6-square foot

garden The lights should be on about 12-16 hours a day for growing herbs or lettuce Lets

assume 12 hours to be conservative That meas were using 12 x 56 watts per day or 672 watt-hours Over a three month period that becomes about 60 kilowatt hours

Lets assume that 6-square foot garden produces 12 healthy heads of lettuce over the three

month period Each head of lettuce has therefore cost you 5 kilowatt hours of electricity

and might weigh a pound wet weight - and at about 95 water content would consist of less than an ounce of dried organic matter

Lettuce

Lettuce grown under LEDs harvested 32 days after planting seeds

TIP Use more blue light to produce sturdier seedlings For leaf crops switch to all red at the end of the growing cycle

Below Constant-yield lettuce garden One square foot is planted every four days 36 days from seed to harvest

Above Four types of lettuce grown in one square foot

LED Grow Lights

LED Grow Lights Ready for Prime Time

Letrsquos face it Everyone that uses high-intensity discharge (HID) garden lights has a

lovehate relationship with them

We love how Metal Halide (MH) or High Pressure Sodium (HPS) lights flood our gardenrsquos

canopy with intense light providing lots of energy for photosynthesis and keeping

internodal distances short We love how we can easily switch between them to match or

manipulate our plantsrsquo growth cycle We love how MH and HPS lights are widely available at reasonable prices

But we hate how much energy these lights consume in our area it costs at least $35 per

month to run a 600 watt MH or HPS light for 12 hours per day more in the summer due to

higher seasonal electric rates HID lights

are one of our most ldquoun-greenrdquo garden

tools with their high energy consumption

low efficiency ratings and mercury-

containing bulbs Critics rightly view them

as inconsistent with earth-friendly gardening methods

A big part of the problem is that HID lights

are inefficient A 400 watt HPS light is

only about 35 efficient which means

that only 35 of the electrical energy

delivered to the bulb is converted into

light with 65 converted into heat

Lighting ballasts are hot too contributing

to high levels of excess heat in most HID-illuminated garden rooms

This waste heat has to go somewhere so

we consume even more energy to cool

and vent gardens that use these lights Air

conditioning is often required and chillers

may be needed to keep nutrient solutions

from getting too hot

HID waste heat increases evaporation

from our reservoirs and growing media

and the transpiration rate of our plants Nutrient and water consumption go up as do the

required flow rates and reliability of our irrigation systems Just about every garden system

is significantly impacted by the waste heat from HID lights

What to do Itrsquos not like we can just turn off our grow lights and wait for something better

T5 fluorescent grow lights are energy efficient and cool running but their lower light output

makes them appropriate for plants that need less light such as leafy greens and foliage

plants At present only an HID garden light can put out enough light to provide a bountiful

harvest in plants that produce large fruit and flowers

The Promise of LED Grow Lights

Wersquove been waiting a long time for garden lights based on light-emitting diodes (LEDs) to

make it to ldquoprime timerdquo NASA and others have been experimenting with LED grow lights

since the mid-80rsquos and we are finally starting to see products reaching the market that reflect their findings These lights represent a major step forward

LED grow lights offer the dual benefit of low energy consumption and low heat generation

Some LED grow lights use so little electricity that they can be powered by a small solar

panel According to their manufacturers todayrsquos LED grow lights consume between 2 and

50 of the electricity used by the HID grow lights they reportedly replace Wersquove yet to see

in real-world application whether these lights will perform as well in the garden as those

ldquocomparablerdquo HIDs particularly for high-light crops

LEDs short for Light Emitting Diodes

are tiny semiconductor chips that

generate light when electrified It takes

a small amount of electricity to make

an LED glow (emit electrons) and the

elements that the diode is made from

determine the light spectrum it emits

An LED is backed by an internal

reflector and encased in an epoxy body

with an integrated lens Together

these components determine the angle

of the light emitted by the diode which

is shaped as a downward-facing cone

Individual LEDs produce relatively

small light cones so they are clustered

into arrays so the light cones overlap

increasing light intensity and coverage

area

LED grow lights are designed to

stimulate photosynthesis by providing light in the frequencies that plants primarily use for

this critical biological process Individual LEDs may contain one of 29 known combinations of

elements that emit light in different colors when excited by electrons Grow light

manufacturers emphasize blue and red LEDs in their fixtures sometimes with other colors

which gives many LED grow lights their distinctive purplish-red color Optimizing the light

spectrum helps in two ways it enhances photosynthesis and saves energy by not generating light in colors that plants do not use

LED Cost Savings

LED grow lights have a longer useful life

than MH or HPS lights as long as 15 years

for some fixtures and thus a lower ldquototal

cost of ownershiprdquo The total cost of

ownership includes the cost to buy the

light use it and replace expired bulbs

One manufacturer estimates that the total

cost of owning an LED grow light over five

years is about half the cost of a

comparable HPS light based on an

analysis that balances the upfront cost to

purchase an LED grow light against lower

electrical costs and eliminating the need

to periodically replace bulbs Their

analysis used an electric rate of $007 per

kilowatt hour ndash here in Southern California

where electric rates are twice as high the

total cost difference between an LED grow

light and a MH or HPS light would be even greater

You may also be able to save space or

move into a smaller space with LED grow

lights There is no need for bulky

reflectors and ventilationcooling

equipment such as fans air conditioners

and ductwork may be eliminated or scaled back The room will also be significantly quieter with fewer noisy fans ballasts and chillers

Thus the promise of LED grow lights has five aspects lower energy consumption lower

heat emissions customizable photosynthetic spectrum lower total cost of ownership and

smaller garden space requirements Can todayrsquos LED grow lights actually deliver these

benefits The answer to that question depends on who you ask Before we get to those

questions however letrsquos take a step back and examine light and photosynthesis a little more closely

Electromagnetic Spectrum and Photosynthesis

Electromagnetic radiation spans a broad range of wavelengths which includes what we

recognize as ldquovisible lightrdquo At the one end of the electromagnetic spectrum are gamma

rays which have a wavelength of 5-10 nanometers (nm) A nanometer is one-billionth of a

meter a very small measure indeed At the other end of the electromagnetic spectrum are

radio waves with a wavelength of 1012 nm Smack in the middle are the wavelengths that

can be seen by the human eye that fall between 380 and 750 nm This part of the

electromagnetic spectrum is what we call ldquovisible lightrdquo

Plants use visible light differently than we do Their leaves contain chlorophyll a compound

vital for photosynthesis the process by which plants convert light into fuel Chlorophyll

molecules are highly selective about the light they absorb blue light primarily in the 460-

480 nm range and red light around 640-680 nm Chlorophyll for the most part reflects

instead of absorbs most green and yellow light which is why plants appear green to our

eyes

Limiting any grow light to just red and blue light would lead to poor results since plants

also use most of rest of the visible spectrum though in lower amounts NASArsquos Biological

Sciences team at the Kennedy Space Center has done extensive research on this subject a

2006 paper published by the International Society of Horticultural Science documented

improvements in lettuce yields when 24 green light was added to LED grow lights that

otherwise produced only red and blue light Including light in the yellow-green spectrum

also helps to visually restore green color to plants making them look more ldquonormalrdquo and

makes it easier to identify garden problems such as nutrient deficiencies or pest attacks

This combination also makes it easier for gardeners to work in their gardens

Increasing the amount of red and blue light reaching the garden isnrsquot an idea limited to LED

grow lights Enhanced-spectrum MH and HPS bulbs such as Hortilux and SolarMax lamps

provide more blue and red light than standard bulbs So water-cooled HID lights according

to their manufacturers Enhanced-spectrum and water-cooled HID lights still put out a lot of

light in yellow-green wavelengths too that look bright to the human eye but donrsquot do much

for our plants An LED grow light designer isnrsquot trying to reproduce sunlight or make up for

the spectral shortcomings of a light originally designed for another purpose Instead they

are trying to create optimal light output for photosynthesis

Current state of the art

So do todayrsquos LED grow lights live up to expectations

Energy consumption is significantly lower for LED lights vs ldquoequivalentrdquo HID lights Most

grow light manufacturers are working to replace the light output of a 400-500 watt HID light

with between 30 and 300 watts of power consumed and some go quite a lot lower The

juryrsquos still out on how these lights truly compare to their HID cousins on garden performance and yield but on the energy promise they seem to perform well

The lights fare well on the heat promise too Most LED grow lights put out very little heat

so do not have any specific cooling requirements A lightrsquos heat output is affected by its

design some lights cluster LEDs in round or square ldquopodsrdquo or ldquorosettesrdquo that are spaced

along horizontal bars These designs help to limit heat accumulation by spacing the LEDs

farther apart Other lights bunch the LEDs close together in a single fixture to provide a

greater light intensity directly below the light These designs can accumulate heat so

generally incorporate heat management features such as heat shielding fans for air cooling

or water cooling

The third promise customized light spectrum is a topic where debates swirl Skeptics do

not believe LEDs can ever produce light that is intense enough to be effective for

photosynthesis no matter what color it is These concerns are based on earlier generation

LEDs that did not put out enough energy to work well as grow lights Todayrsquos ldquothird

generationrdquo LEDs reportedly solve this problem by putting out up to three watts of light

energy per LED a 20-50 fold improvement over second-generation LEDs New-generation

LEDs also have a wider ldquobeam anglerdquo that permits an LED to project light across a 120

degree arc instead of mostly just straight down (ldquopin pointrdquo lighting) This means wider light cones improving light intensity and coverage at the garden canopy

Passionate debates about LED grow light design and effectiveness are waged on a regular

basis in online gardening communities Some posts describe LED grow light trials people are

conducting in their homes While these posts are interesting reading and therersquos a lot to be

learned from them they should also be taken with a grain of salt Many hobbyists want to

debate whether LED grow lights are or can be effective The academic and scientific

communities satisfied for some time that LED grow lights are effective have moved on to

figuring out ldquohowrdquo

Updating Garden Methods for LEDs

One point that LED grow light manufacturers emphasize is that we must update our

gardening methods to use LED grow lights to their best advantage Using an LED grow light

without changing gardening methods will likely result in a disappointing outcome The first

caution is to not overwater Yoursquove eliminated one of the largest sources of heat in your

garden your HID garden lights

With less heat your plants consume less nutrient solution and less of it evaporates thus

less solution is needed One lighting manufacturer also suggests using a weaker nutrient

solution to match lower plant transpiration rates Less solution and less nutrients used this

should be good news right Yes and no Reservoirs can be smaller saving money and

space Fewer expensive bottles of hydroponic nutrient solutions are needed

The dark side is subtle but compelling the most

frequent cause of indoor plant death is

overwatering Itrsquos just as true for plants in a fully

automated indoor garden as it is for an African

violet on the kitchen windowsill Those accustomed

to gardening under HID lights will find that itrsquos

extremely easy to overwater under LED grow

lights Your plants simply need less water when there is less heat

Overwatering can lead to root rot or drowning if itrsquos

not caught and corrected right away When using

LED grow lights be sure to select a porous growing

media to provide adequate drainage and plenty of

air space in the root zone Also let your plants

almost dry more between feedings Overwatering

can also increase garden humidity levels which

can promote the development of fungus and other

garden ills Keep a close watch on growing media

moisture levels and garden relative humidity when

using LED grow lights An LED grow light that emits

some UV-A spectrum (invisible but felt as heat)

may help to kill or retard mildew Maintaining constant air movement within the garden

using oscillating or fixed fans will also help to keep mold and mildew in check

Grow light manufacturers also recommend supplementing the garden atmosphere with

carbon dioxide (CO2) While supplemental CO2 will improve the yield of any garden when

properly applied there are two particular benefits when using CO2 with LED grow lights

First even though an LED grow light may look dim to the human eye it is putting out a lot

of light energy in the spectrum needed for photosynthesis ndash ideally more than the plants

would receive under ldquocomparablerdquo MH or HPS lights Plants need higher CO2 levels in order

to turn this additional light into fuel The second benefit is that with lower heat output there

is less need to vent or air condition the garden space Itrsquos easier to seal the garden environment for CO2 when itrsquos not as hot

Top Two Concerns

We asked several LED lighting manufacturers about the concerns customers express when

considering an LED grow light Two primary concerns emerged

The first is the price for LED grow lights LED grow lights can be purchased on eBay for as

little as $9 for a screw-in replacement grow bulb to as much as $1500 for a water-cooled

garden light fixture reported to be equivalent to a 400- to 500 watt HPS light Donrsquot be

misled by the low price on some of the LED lights on eBay ndash they often include lower-

output inferior LEDs and some of them are recycled traffic signal lights A large number of

these inexpensive LED ldquogrow lightsrdquo may be needed to provide illumination for a standard-

sized hobby garden buyer beware A home gardener should expect to spend between $500

and $1500 for LED grow lights to illuminate a 3rsquo x 3rsquo growing space The ldquototal cost of

ownershiprdquo models discussed earlier are one way to understand the price issue LED grow

lights require a larger up-front investment which should be more than offset by reduced operating costs going forward

The second concern is that nobody

wants to go first More people are

interested in LED grow lights than are

ready to start using them Gardeners

do not want their crop to wind up as

the ldquoguinea pigrdquo in a failed garden

lighting experiment A lot of trials and

research have been conducted in

research laboratories that show LED

grow lights to be effective and cost-

efficient But those trials were done in

a laboratory setting Whatrsquos missing

are verifiable and repeatable

consumer-oriented trials that put LED

grow lights up against their HID

counterparts in conditions that

resemble a hobbyist indoor garden

room Until that happens individual

gardeners can experiment with LED grow lights on their own either on a small scale or by segregating a small number of plants within their garden for trials

Looking Ahead

What is the future of LED grow lights Near-term we should expect to see a wider variety of

LED grow lights coming onto the market These lights will increasingly include higher output

LEDs in a variety of light colors and configurations We expect to see combination lights

hitting the market using LED plus T5 fluorescent or HID garden lights to provide a more balanced spectrum than available from these garden lights used alone

We are starting to see LED grow lights designed to support different plant growth stages

such as grow and bloom and should expect lights to be introduced for specific plants such

as tomatoes herbs or orchids We will see continued improvements in light output

particularly as fourth-generation LEDs continue their migration from the lab to the market

Prices will begin to come down when sales volume increases

In the long run LED lighting could

obsolete almost every other type of

lighting Retrofit LED lamps that fit

into standard fluorescent lighting

fixtures are already available and

LED fixtures are in the works that

will replace street lights stadium

lights and other interior and

exterior lights Already Amsterdam

and Rotterdam in the Netherlands

are testing LED street lighting and

press reports indicate that other

major cities are considering similar trials

LED grow lights will be swept ahead

with the tide of mostly government-

funded research and development

currently underway Research

dollars invested by NASA and other

government agencies around the

globe are fueling tremendous

advances in LED lighting

technologies The energy saving

potential of LED lights is something

these entities cannot ignore if we

can find a way to consume less

energy to light up public and

private spaces we may be able to

postpone or scratch plans to build

new power plants or buy time until we are able to commercialize sustainable methods to generate and transport electricity

There is a lot of promise associated with LED grow lights but there are also unanswered

questions and unresolved debates The products that are available today should produce an

acceptable result so long as the gardener makes appropriate changes to their gardening

methods Wersquore looking forward to further articles and reports that describe how LED grow

lights perform against standard MH and HPS grow lights Wersquore hopeful about how LED grow

lights will fare in such comparisons

LED Growing Lights

Grow more plants with less electricity

Are LED growing lights better than fluorescent metal halide or high pressure sodium grow

lights Will they improve plant growth and will they use less electricity Is growing plants with LED growing lights environmentally friendly

Plants dont use the full visible spectrum to photosynthecize They predominantly use cool

(violet-blue and blue) and warm (orange-red) wavelengths which is a reflection of the

typical colors of natural night on a seasonal basis In the summer months when the sun is

more directly overhead cool colors predominate and tend to encourage healthy vegetative

growth while in spring and fall warm colors take over and tend to encourage flowering and fruiting

A typical metal halide grow light puts out much of its output in wavelength ranges that

plants do not use - cyan green yellow - and very little in the violet or blue regions So with

a metal halide grow light you are typically wasting much of the light shining down on your

plants A daylight metal halide light is more in the blue spectrum and so is useful for the

vegetative stage of growth but not for flowering or fruiting High pressure sodium lights

tend more to the warm red end of the spectrum and so are chiefly useful for flowering and fruiting

You can create your own LED growing lights by combining red and blue LED lights in roughly

a two- to-one proportion (two blue to one red) or buy an LED set designed specifically for

indoor growing which has blue and red LED grow lights in an appropriate proportion LED

grow lights have the benefit of low heat output so you dont need to worry about drying out

the soil or scorching the plants and they use very little electricity For example GlowPanel

LED growing lights cover a 15 square foot area (they are roughly 15 inches on a side) and

consume just 14 watts For growing purposes this light would be suitable for starting

seedlings or for growing herbs or lettuce indoors but is at the lower end of required light output for growing vegetables

Is it green to use LED growing lights Well its definitely an improvement to switch from

any of the other technologies as the amount of electricity youll use for the same amount of

growth is reduced significantly because of the concentration of light in the desired ranges of

the spectrum and because of the improved efficiency of LEDs But in absolute terms I

personally feel that LED growing lights should be used sparingly unless you have a source of carbon-neutral electricity that no one else has a use for

Why Lets consider a 6-square-foot herb garden using the GlowPanel LED growing lights

These lights consume 14 watts each for 15 square feet or 56 watts for the 6-square foot

garden The lights should be on about 12-16 hours a day for growing herbs or lettuce Lets

assume 12 hours to be conservative That meas were using 12 x 56 watts per day or 672 watt-hours Over a three month period that becomes about 60 kilowatt hours

Lets assume that 6-square foot garden produces 12 healthy heads of lettuce over the three

month period Each head of lettuce has therefore cost you 5 kilowatt hours of electricity

and might weigh a pound wet weight - and at about 95 water content would consist of less than an ounce of dried organic matter

Above Four types of lettuce grown in one square foot

LED Grow Lights

LED Grow Lights Ready for Prime Time

Letrsquos face it Everyone that uses high-intensity discharge (HID) garden lights has a

lovehate relationship with them

We love how Metal Halide (MH) or High Pressure Sodium (HPS) lights flood our gardenrsquos

canopy with intense light providing lots of energy for photosynthesis and keeping

internodal distances short We love how we can easily switch between them to match or

manipulate our plantsrsquo growth cycle We love how MH and HPS lights are widely available at reasonable prices

But we hate how much energy these lights consume in our area it costs at least $35 per

month to run a 600 watt MH or HPS light for 12 hours per day more in the summer due to

higher seasonal electric rates HID lights

are one of our most ldquoun-greenrdquo garden

tools with their high energy consumption

low efficiency ratings and mercury-

containing bulbs Critics rightly view them

as inconsistent with earth-friendly gardening methods

A big part of the problem is that HID lights

are inefficient A 400 watt HPS light is

only about 35 efficient which means

that only 35 of the electrical energy

delivered to the bulb is converted into

light with 65 converted into heat

Lighting ballasts are hot too contributing

to high levels of excess heat in most HID-illuminated garden rooms

This waste heat has to go somewhere so

we consume even more energy to cool

and vent gardens that use these lights Air

conditioning is often required and chillers

may be needed to keep nutrient solutions

from getting too hot

HID waste heat increases evaporation

from our reservoirs and growing media

and the transpiration rate of our plants Nutrient and water consumption go up as do the

required flow rates and reliability of our irrigation systems Just about every garden system

is significantly impacted by the waste heat from HID lights

What to do Itrsquos not like we can just turn off our grow lights and wait for something better

T5 fluorescent grow lights are energy efficient and cool running but their lower light output

makes them appropriate for plants that need less light such as leafy greens and foliage

plants At present only an HID garden light can put out enough light to provide a bountiful

harvest in plants that produce large fruit and flowers

The Promise of LED Grow Lights

Wersquove been waiting a long time for garden lights based on light-emitting diodes (LEDs) to

make it to ldquoprime timerdquo NASA and others have been experimenting with LED grow lights

since the mid-80rsquos and we are finally starting to see products reaching the market that reflect their findings These lights represent a major step forward

LED grow lights offer the dual benefit of low energy consumption and low heat generation

Some LED grow lights use so little electricity that they can be powered by a small solar

panel According to their manufacturers todayrsquos LED grow lights consume between 2 and

50 of the electricity used by the HID grow lights they reportedly replace Wersquove yet to see

in real-world application whether these lights will perform as well in the garden as those

ldquocomparablerdquo HIDs particularly for high-light crops

LEDs short for Light Emitting Diodes

are tiny semiconductor chips that

generate light when electrified It takes

a small amount of electricity to make

an LED glow (emit electrons) and the

elements that the diode is made from

determine the light spectrum it emits

An LED is backed by an internal

reflector and encased in an epoxy body

with an integrated lens Together

these components determine the angle

of the light emitted by the diode which

is shaped as a downward-facing cone

Individual LEDs produce relatively

small light cones so they are clustered

into arrays so the light cones overlap

increasing light intensity and coverage

area

LED grow lights are designed to

stimulate photosynthesis by providing light in the frequencies that plants primarily use for

this critical biological process Individual LEDs may contain one of 29 known combinations of

elements that emit light in different colors when excited by electrons Grow light

manufacturers emphasize blue and red LEDs in their fixtures sometimes with other colors

which gives many LED grow lights their distinctive purplish-red color Optimizing the light

spectrum helps in two ways it enhances photosynthesis and saves energy by not generating light in colors that plants do not use

LED Cost Savings

LED grow lights have a longer useful life

than MH or HPS lights as long as 15 years

for some fixtures and thus a lower ldquototal

cost of ownershiprdquo The total cost of

ownership includes the cost to buy the

light use it and replace expired bulbs

One manufacturer estimates that the total

cost of owning an LED grow light over five

years is about half the cost of a

comparable HPS light based on an

analysis that balances the upfront cost to

purchase an LED grow light against lower

electrical costs and eliminating the need

to periodically replace bulbs Their

analysis used an electric rate of $007 per

kilowatt hour ndash here in Southern California

where electric rates are twice as high the

total cost difference between an LED grow

light and a MH or HPS light would be even greater

You may also be able to save space or

move into a smaller space with LED grow

lights There is no need for bulky

reflectors and ventilationcooling

equipment such as fans air conditioners

and ductwork may be eliminated or scaled back The room will also be significantly quieter with fewer noisy fans ballasts and chillers

Thus the promise of LED grow lights has five aspects lower energy consumption lower

heat emissions customizable photosynthetic spectrum lower total cost of ownership and

smaller garden space requirements Can todayrsquos LED grow lights actually deliver these

benefits The answer to that question depends on who you ask Before we get to those

questions however letrsquos take a step back and examine light and photosynthesis a little more closely

Electromagnetic Spectrum and Photosynthesis

Electromagnetic radiation spans a broad range of wavelengths which includes what we

recognize as ldquovisible lightrdquo At the one end of the electromagnetic spectrum are gamma

rays which have a wavelength of 5-10 nanometers (nm) A nanometer is one-billionth of a

meter a very small measure indeed At the other end of the electromagnetic spectrum are

radio waves with a wavelength of 1012 nm Smack in the middle are the wavelengths that

can be seen by the human eye that fall between 380 and 750 nm This part of the

electromagnetic spectrum is what we call ldquovisible lightrdquo

Plants use visible light differently than we do Their leaves contain chlorophyll a compound

vital for photosynthesis the process by which plants convert light into fuel Chlorophyll

molecules are highly selective about the light they absorb blue light primarily in the 460-

480 nm range and red light around 640-680 nm Chlorophyll for the most part reflects

instead of absorbs most green and yellow light which is why plants appear green to our

eyes

Limiting any grow light to just red and blue light would lead to poor results since plants

also use most of rest of the visible spectrum though in lower amounts NASArsquos Biological

Sciences team at the Kennedy Space Center has done extensive research on this subject a

2006 paper published by the International Society of Horticultural Science documented

improvements in lettuce yields when 24 green light was added to LED grow lights that

otherwise produced only red and blue light Including light in the yellow-green spectrum

also helps to visually restore green color to plants making them look more ldquonormalrdquo and

makes it easier to identify garden problems such as nutrient deficiencies or pest attacks

This combination also makes it easier for gardeners to work in their gardens

Increasing the amount of red and blue light reaching the garden isnrsquot an idea limited to LED

grow lights Enhanced-spectrum MH and HPS bulbs such as Hortilux and SolarMax lamps

provide more blue and red light than standard bulbs So water-cooled HID lights according

to their manufacturers Enhanced-spectrum and water-cooled HID lights still put out a lot of

light in yellow-green wavelengths too that look bright to the human eye but donrsquot do much

for our plants An LED grow light designer isnrsquot trying to reproduce sunlight or make up for

the spectral shortcomings of a light originally designed for another purpose Instead they

are trying to create optimal light output for photosynthesis

Current state of the art

So do todayrsquos LED grow lights live up to expectations

Energy consumption is significantly lower for LED lights vs ldquoequivalentrdquo HID lights Most

grow light manufacturers are working to replace the light output of a 400-500 watt HID light

with between 30 and 300 watts of power consumed and some go quite a lot lower The

juryrsquos still out on how these lights truly compare to their HID cousins on garden performance and yield but on the energy promise they seem to perform well

The lights fare well on the heat promise too Most LED grow lights put out very little heat

so do not have any specific cooling requirements A lightrsquos heat output is affected by its

design some lights cluster LEDs in round or square ldquopodsrdquo or ldquorosettesrdquo that are spaced

along horizontal bars These designs help to limit heat accumulation by spacing the LEDs

farther apart Other lights bunch the LEDs close together in a single fixture to provide a

greater light intensity directly below the light These designs can accumulate heat so

generally incorporate heat management features such as heat shielding fans for air cooling

or water cooling

The third promise customized light spectrum is a topic where debates swirl Skeptics do

not believe LEDs can ever produce light that is intense enough to be effective for

photosynthesis no matter what color it is These concerns are based on earlier generation

LEDs that did not put out enough energy to work well as grow lights Todayrsquos ldquothird

generationrdquo LEDs reportedly solve this problem by putting out up to three watts of light

energy per LED a 20-50 fold improvement over second-generation LEDs New-generation

LEDs also have a wider ldquobeam anglerdquo that permits an LED to project light across a 120

degree arc instead of mostly just straight down (ldquopin pointrdquo lighting) This means wider light cones improving light intensity and coverage at the garden canopy

Passionate debates about LED grow light design and effectiveness are waged on a regular

basis in online gardening communities Some posts describe LED grow light trials people are

conducting in their homes While these posts are interesting reading and therersquos a lot to be

learned from them they should also be taken with a grain of salt Many hobbyists want to

debate whether LED grow lights are or can be effective The academic and scientific

communities satisfied for some time that LED grow lights are effective have moved on to

figuring out ldquohowrdquo

Updating Garden Methods for LEDs

One point that LED grow light manufacturers emphasize is that we must update our

gardening methods to use LED grow lights to their best advantage Using an LED grow light

without changing gardening methods will likely result in a disappointing outcome The first

caution is to not overwater Yoursquove eliminated one of the largest sources of heat in your

garden your HID garden lights

With less heat your plants consume less nutrient solution and less of it evaporates thus

less solution is needed One lighting manufacturer also suggests using a weaker nutrient

solution to match lower plant transpiration rates Less solution and less nutrients used this

should be good news right Yes and no Reservoirs can be smaller saving money and

space Fewer expensive bottles of hydroponic nutrient solutions are needed

The dark side is subtle but compelling the most

frequent cause of indoor plant death is

overwatering Itrsquos just as true for plants in a fully

automated indoor garden as it is for an African

violet on the kitchen windowsill Those accustomed

to gardening under HID lights will find that itrsquos

extremely easy to overwater under LED grow

lights Your plants simply need less water when there is less heat

Overwatering can lead to root rot or drowning if itrsquos

not caught and corrected right away When using

LED grow lights be sure to select a porous growing

media to provide adequate drainage and plenty of

air space in the root zone Also let your plants

almost dry more between feedings Overwatering

can also increase garden humidity levels which

can promote the development of fungus and other

garden ills Keep a close watch on growing media

moisture levels and garden relative humidity when

using LED grow lights An LED grow light that emits

some UV-A spectrum (invisible but felt as heat)

may help to kill or retard mildew Maintaining constant air movement within the garden

using oscillating or fixed fans will also help to keep mold and mildew in check

Grow light manufacturers also recommend supplementing the garden atmosphere with

carbon dioxide (CO2) While supplemental CO2 will improve the yield of any garden when

properly applied there are two particular benefits when using CO2 with LED grow lights

First even though an LED grow light may look dim to the human eye it is putting out a lot

of light energy in the spectrum needed for photosynthesis ndash ideally more than the plants

would receive under ldquocomparablerdquo MH or HPS lights Plants need higher CO2 levels in order

to turn this additional light into fuel The second benefit is that with lower heat output there

is less need to vent or air condition the garden space Itrsquos easier to seal the garden environment for CO2 when itrsquos not as hot

Top Two Concerns

We asked several LED lighting manufacturers about the concerns customers express when

considering an LED grow light Two primary concerns emerged

The first is the price for LED grow lights LED grow lights can be purchased on eBay for as

little as $9 for a screw-in replacement grow bulb to as much as $1500 for a water-cooled

garden light fixture reported to be equivalent to a 400- to 500 watt HPS light Donrsquot be

misled by the low price on some of the LED lights on eBay ndash they often include lower-

output inferior LEDs and some of them are recycled traffic signal lights A large number of

these inexpensive LED ldquogrow lightsrdquo may be needed to provide illumination for a standard-

sized hobby garden buyer beware A home gardener should expect to spend between $500

and $1500 for LED grow lights to illuminate a 3rsquo x 3rsquo growing space The ldquototal cost of

ownershiprdquo models discussed earlier are one way to understand the price issue LED grow

lights require a larger up-front investment which should be more than offset by reduced operating costs going forward

The second concern is that nobody

wants to go first More people are

interested in LED grow lights than are

ready to start using them Gardeners

do not want their crop to wind up as

the ldquoguinea pigrdquo in a failed garden

lighting experiment A lot of trials and

research have been conducted in

research laboratories that show LED

grow lights to be effective and cost-

efficient But those trials were done in

a laboratory setting Whatrsquos missing

are verifiable and repeatable

consumer-oriented trials that put LED

grow lights up against their HID

counterparts in conditions that

resemble a hobbyist indoor garden

room Until that happens individual

gardeners can experiment with LED grow lights on their own either on a small scale or by segregating a small number of plants within their garden for trials

Looking Ahead

What is the future of LED grow lights Near-term we should expect to see a wider variety of

LED grow lights coming onto the market These lights will increasingly include higher output

LEDs in a variety of light colors and configurations We expect to see combination lights

hitting the market using LED plus T5 fluorescent or HID garden lights to provide a more balanced spectrum than available from these garden lights used alone

We are starting to see LED grow lights designed to support different plant growth stages

such as grow and bloom and should expect lights to be introduced for specific plants such

as tomatoes herbs or orchids We will see continued improvements in light output

particularly as fourth-generation LEDs continue their migration from the lab to the market

Prices will begin to come down when sales volume increases

In the long run LED lighting could

obsolete almost every other type of

lighting Retrofit LED lamps that fit

into standard fluorescent lighting

fixtures are already available and

LED fixtures are in the works that

will replace street lights stadium

lights and other interior and

exterior lights Already Amsterdam

and Rotterdam in the Netherlands

are testing LED street lighting and

press reports indicate that other

major cities are considering similar trials

LED grow lights will be swept ahead

with the tide of mostly government-

funded research and development

currently underway Research

dollars invested by NASA and other

government agencies around the

globe are fueling tremendous

advances in LED lighting

technologies The energy saving

potential of LED lights is something

these entities cannot ignore if we

can find a way to consume less

energy to light up public and

private spaces we may be able to

postpone or scratch plans to build

new power plants or buy time until we are able to commercialize sustainable methods to generate and transport electricity

There is a lot of promise associated with LED grow lights but there are also unanswered

questions and unresolved debates The products that are available today should produce an

acceptable result so long as the gardener makes appropriate changes to their gardening

methods Wersquore looking forward to further articles and reports that describe how LED grow

lights perform against standard MH and HPS grow lights Wersquore hopeful about how LED grow

lights will fare in such comparisons

LED Growing Lights

Grow more plants with less electricity

Are LED growing lights better than fluorescent metal halide or high pressure sodium grow

lights Will they improve plant growth and will they use less electricity Is growing plants with LED growing lights environmentally friendly

Plants dont use the full visible spectrum to photosynthecize They predominantly use cool

(violet-blue and blue) and warm (orange-red) wavelengths which is a reflection of the

typical colors of natural night on a seasonal basis In the summer months when the sun is

more directly overhead cool colors predominate and tend to encourage healthy vegetative

growth while in spring and fall warm colors take over and tend to encourage flowering and fruiting

A typical metal halide grow light puts out much of its output in wavelength ranges that

plants do not use - cyan green yellow - and very little in the violet or blue regions So with

a metal halide grow light you are typically wasting much of the light shining down on your

plants A daylight metal halide light is more in the blue spectrum and so is useful for the

vegetative stage of growth but not for flowering or fruiting High pressure sodium lights

tend more to the warm red end of the spectrum and so are chiefly useful for flowering and fruiting

You can create your own LED growing lights by combining red and blue LED lights in roughly

a two- to-one proportion (two blue to one red) or buy an LED set designed specifically for

indoor growing which has blue and red LED grow lights in an appropriate proportion LED

grow lights have the benefit of low heat output so you dont need to worry about drying out

the soil or scorching the plants and they use very little electricity For example GlowPanel

LED growing lights cover a 15 square foot area (they are roughly 15 inches on a side) and

consume just 14 watts For growing purposes this light would be suitable for starting

seedlings or for growing herbs or lettuce indoors but is at the lower end of required light output for growing vegetables

Is it green to use LED growing lights Well its definitely an improvement to switch from

any of the other technologies as the amount of electricity youll use for the same amount of

growth is reduced significantly because of the concentration of light in the desired ranges of

the spectrum and because of the improved efficiency of LEDs But in absolute terms I

personally feel that LED growing lights should be used sparingly unless you have a source of carbon-neutral electricity that no one else has a use for

Why Lets consider a 6-square-foot herb garden using the GlowPanel LED growing lights

These lights consume 14 watts each for 15 square feet or 56 watts for the 6-square foot

garden The lights should be on about 12-16 hours a day for growing herbs or lettuce Lets

assume 12 hours to be conservative That meas were using 12 x 56 watts per day or 672 watt-hours Over a three month period that becomes about 60 kilowatt hours

Lets assume that 6-square foot garden produces 12 healthy heads of lettuce over the three

month period Each head of lettuce has therefore cost you 5 kilowatt hours of electricity

and might weigh a pound wet weight - and at about 95 water content would consist of less than an ounce of dried organic matter

LED Grow Lights

LED Grow Lights Ready for Prime Time

Letrsquos face it Everyone that uses high-intensity discharge (HID) garden lights has a

lovehate relationship with them

We love how Metal Halide (MH) or High Pressure Sodium (HPS) lights flood our gardenrsquos

canopy with intense light providing lots of energy for photosynthesis and keeping

internodal distances short We love how we can easily switch between them to match or

manipulate our plantsrsquo growth cycle We love how MH and HPS lights are widely available at reasonable prices

But we hate how much energy these lights consume in our area it costs at least $35 per

month to run a 600 watt MH or HPS light for 12 hours per day more in the summer due to

higher seasonal electric rates HID lights

are one of our most ldquoun-greenrdquo garden

tools with their high energy consumption

low efficiency ratings and mercury-

containing bulbs Critics rightly view them

as inconsistent with earth-friendly gardening methods

A big part of the problem is that HID lights

are inefficient A 400 watt HPS light is

only about 35 efficient which means

that only 35 of the electrical energy

delivered to the bulb is converted into

light with 65 converted into heat

Lighting ballasts are hot too contributing

to high levels of excess heat in most HID-illuminated garden rooms

This waste heat has to go somewhere so

we consume even more energy to cool

and vent gardens that use these lights Air

conditioning is often required and chillers

may be needed to keep nutrient solutions

from getting too hot

HID waste heat increases evaporation

from our reservoirs and growing media

and the transpiration rate of our plants Nutrient and water consumption go up as do the

required flow rates and reliability of our irrigation systems Just about every garden system

is significantly impacted by the waste heat from HID lights

What to do Itrsquos not like we can just turn off our grow lights and wait for something better

T5 fluorescent grow lights are energy efficient and cool running but their lower light output

makes them appropriate for plants that need less light such as leafy greens and foliage

plants At present only an HID garden light can put out enough light to provide a bountiful

harvest in plants that produce large fruit and flowers

The Promise of LED Grow Lights

Wersquove been waiting a long time for garden lights based on light-emitting diodes (LEDs) to

make it to ldquoprime timerdquo NASA and others have been experimenting with LED grow lights

since the mid-80rsquos and we are finally starting to see products reaching the market that reflect their findings These lights represent a major step forward

LED grow lights offer the dual benefit of low energy consumption and low heat generation

Some LED grow lights use so little electricity that they can be powered by a small solar

panel According to their manufacturers todayrsquos LED grow lights consume between 2 and

50 of the electricity used by the HID grow lights they reportedly replace Wersquove yet to see

in real-world application whether these lights will perform as well in the garden as those

ldquocomparablerdquo HIDs particularly for high-light crops

LEDs short for Light Emitting Diodes

are tiny semiconductor chips that

generate light when electrified It takes

a small amount of electricity to make

an LED glow (emit electrons) and the

elements that the diode is made from

determine the light spectrum it emits

An LED is backed by an internal

reflector and encased in an epoxy body

with an integrated lens Together

these components determine the angle

of the light emitted by the diode which

is shaped as a downward-facing cone

Individual LEDs produce relatively

small light cones so they are clustered

into arrays so the light cones overlap

increasing light intensity and coverage

area

LED grow lights are designed to

stimulate photosynthesis by providing light in the frequencies that plants primarily use for

this critical biological process Individual LEDs may contain one of 29 known combinations of

elements that emit light in different colors when excited by electrons Grow light

manufacturers emphasize blue and red LEDs in their fixtures sometimes with other colors

which gives many LED grow lights their distinctive purplish-red color Optimizing the light

spectrum helps in two ways it enhances photosynthesis and saves energy by not generating light in colors that plants do not use

LED Cost Savings

LED grow lights have a longer useful life

than MH or HPS lights as long as 15 years

for some fixtures and thus a lower ldquototal

cost of ownershiprdquo The total cost of

ownership includes the cost to buy the

light use it and replace expired bulbs

One manufacturer estimates that the total

cost of owning an LED grow light over five

years is about half the cost of a

comparable HPS light based on an

analysis that balances the upfront cost to

purchase an LED grow light against lower

electrical costs and eliminating the need

to periodically replace bulbs Their

analysis used an electric rate of $007 per

kilowatt hour ndash here in Southern California

where electric rates are twice as high the

total cost difference between an LED grow

light and a MH or HPS light would be even greater

You may also be able to save space or

move into a smaller space with LED grow

lights There is no need for bulky

reflectors and ventilationcooling

equipment such as fans air conditioners

and ductwork may be eliminated or scaled back The room will also be significantly quieter with fewer noisy fans ballasts and chillers

Thus the promise of LED grow lights has five aspects lower energy consumption lower

heat emissions customizable photosynthetic spectrum lower total cost of ownership and

smaller garden space requirements Can todayrsquos LED grow lights actually deliver these

benefits The answer to that question depends on who you ask Before we get to those

questions however letrsquos take a step back and examine light and photosynthesis a little more closely

Electromagnetic Spectrum and Photosynthesis

Electromagnetic radiation spans a broad range of wavelengths which includes what we

recognize as ldquovisible lightrdquo At the one end of the electromagnetic spectrum are gamma

rays which have a wavelength of 5-10 nanometers (nm) A nanometer is one-billionth of a

meter a very small measure indeed At the other end of the electromagnetic spectrum are

radio waves with a wavelength of 1012 nm Smack in the middle are the wavelengths that

can be seen by the human eye that fall between 380 and 750 nm This part of the

electromagnetic spectrum is what we call ldquovisible lightrdquo

Plants use visible light differently than we do Their leaves contain chlorophyll a compound

vital for photosynthesis the process by which plants convert light into fuel Chlorophyll

molecules are highly selective about the light they absorb blue light primarily in the 460-

480 nm range and red light around 640-680 nm Chlorophyll for the most part reflects

instead of absorbs most green and yellow light which is why plants appear green to our

eyes

Limiting any grow light to just red and blue light would lead to poor results since plants

also use most of rest of the visible spectrum though in lower amounts NASArsquos Biological

Sciences team at the Kennedy Space Center has done extensive research on this subject a

2006 paper published by the International Society of Horticultural Science documented

improvements in lettuce yields when 24 green light was added to LED grow lights that

otherwise produced only red and blue light Including light in the yellow-green spectrum

also helps to visually restore green color to plants making them look more ldquonormalrdquo and

makes it easier to identify garden problems such as nutrient deficiencies or pest attacks

This combination also makes it easier for gardeners to work in their gardens

Increasing the amount of red and blue light reaching the garden isnrsquot an idea limited to LED

grow lights Enhanced-spectrum MH and HPS bulbs such as Hortilux and SolarMax lamps

provide more blue and red light than standard bulbs So water-cooled HID lights according

to their manufacturers Enhanced-spectrum and water-cooled HID lights still put out a lot of

light in yellow-green wavelengths too that look bright to the human eye but donrsquot do much

for our plants An LED grow light designer isnrsquot trying to reproduce sunlight or make up for

the spectral shortcomings of a light originally designed for another purpose Instead they

are trying to create optimal light output for photosynthesis

Current state of the art

So do todayrsquos LED grow lights live up to expectations

Energy consumption is significantly lower for LED lights vs ldquoequivalentrdquo HID lights Most

grow light manufacturers are working to replace the light output of a 400-500 watt HID light

with between 30 and 300 watts of power consumed and some go quite a lot lower The

juryrsquos still out on how these lights truly compare to their HID cousins on garden performance and yield but on the energy promise they seem to perform well

The lights fare well on the heat promise too Most LED grow lights put out very little heat

so do not have any specific cooling requirements A lightrsquos heat output is affected by its

design some lights cluster LEDs in round or square ldquopodsrdquo or ldquorosettesrdquo that are spaced

along horizontal bars These designs help to limit heat accumulation by spacing the LEDs

farther apart Other lights bunch the LEDs close together in a single fixture to provide a

greater light intensity directly below the light These designs can accumulate heat so

generally incorporate heat management features such as heat shielding fans for air cooling

or water cooling

The third promise customized light spectrum is a topic where debates swirl Skeptics do

not believe LEDs can ever produce light that is intense enough to be effective for

photosynthesis no matter what color it is These concerns are based on earlier generation

LEDs that did not put out enough energy to work well as grow lights Todayrsquos ldquothird

generationrdquo LEDs reportedly solve this problem by putting out up to three watts of light

energy per LED a 20-50 fold improvement over second-generation LEDs New-generation

LEDs also have a wider ldquobeam anglerdquo that permits an LED to project light across a 120

degree arc instead of mostly just straight down (ldquopin pointrdquo lighting) This means wider light cones improving light intensity and coverage at the garden canopy

Passionate debates about LED grow light design and effectiveness are waged on a regular

basis in online gardening communities Some posts describe LED grow light trials people are

conducting in their homes While these posts are interesting reading and therersquos a lot to be

learned from them they should also be taken with a grain of salt Many hobbyists want to

debate whether LED grow lights are or can be effective The academic and scientific

communities satisfied for some time that LED grow lights are effective have moved on to

figuring out ldquohowrdquo

Updating Garden Methods for LEDs

One point that LED grow light manufacturers emphasize is that we must update our

gardening methods to use LED grow lights to their best advantage Using an LED grow light

without changing gardening methods will likely result in a disappointing outcome The first

caution is to not overwater Yoursquove eliminated one of the largest sources of heat in your

garden your HID garden lights

With less heat your plants consume less nutrient solution and less of it evaporates thus

less solution is needed One lighting manufacturer also suggests using a weaker nutrient

solution to match lower plant transpiration rates Less solution and less nutrients used this

should be good news right Yes and no Reservoirs can be smaller saving money and

space Fewer expensive bottles of hydroponic nutrient solutions are needed

The dark side is subtle but compelling the most

frequent cause of indoor plant death is

overwatering Itrsquos just as true for plants in a fully

automated indoor garden as it is for an African

violet on the kitchen windowsill Those accustomed

to gardening under HID lights will find that itrsquos

extremely easy to overwater under LED grow

lights Your plants simply need less water when there is less heat

Overwatering can lead to root rot or drowning if itrsquos

not caught and corrected right away When using

LED grow lights be sure to select a porous growing

media to provide adequate drainage and plenty of

air space in the root zone Also let your plants

almost dry more between feedings Overwatering

can also increase garden humidity levels which

can promote the development of fungus and other

garden ills Keep a close watch on growing media

moisture levels and garden relative humidity when

using LED grow lights An LED grow light that emits

some UV-A spectrum (invisible but felt as heat)

may help to kill or retard mildew Maintaining constant air movement within the garden

using oscillating or fixed fans will also help to keep mold and mildew in check

Grow light manufacturers also recommend supplementing the garden atmosphere with

carbon dioxide (CO2) While supplemental CO2 will improve the yield of any garden when

properly applied there are two particular benefits when using CO2 with LED grow lights

First even though an LED grow light may look dim to the human eye it is putting out a lot

of light energy in the spectrum needed for photosynthesis ndash ideally more than the plants

would receive under ldquocomparablerdquo MH or HPS lights Plants need higher CO2 levels in order

to turn this additional light into fuel The second benefit is that with lower heat output there

is less need to vent or air condition the garden space Itrsquos easier to seal the garden environment for CO2 when itrsquos not as hot

Top Two Concerns

We asked several LED lighting manufacturers about the concerns customers express when

considering an LED grow light Two primary concerns emerged

The first is the price for LED grow lights LED grow lights can be purchased on eBay for as

little as $9 for a screw-in replacement grow bulb to as much as $1500 for a water-cooled

garden light fixture reported to be equivalent to a 400- to 500 watt HPS light Donrsquot be

misled by the low price on some of the LED lights on eBay ndash they often include lower-

output inferior LEDs and some of them are recycled traffic signal lights A large number of

these inexpensive LED ldquogrow lightsrdquo may be needed to provide illumination for a standard-

sized hobby garden buyer beware A home gardener should expect to spend between $500

and $1500 for LED grow lights to illuminate a 3rsquo x 3rsquo growing space The ldquototal cost of

ownershiprdquo models discussed earlier are one way to understand the price issue LED grow

lights require a larger up-front investment which should be more than offset by reduced operating costs going forward

The second concern is that nobody

wants to go first More people are

interested in LED grow lights than are

ready to start using them Gardeners

do not want their crop to wind up as

the ldquoguinea pigrdquo in a failed garden

lighting experiment A lot of trials and

research have been conducted in

research laboratories that show LED

grow lights to be effective and cost-

efficient But those trials were done in

a laboratory setting Whatrsquos missing

are verifiable and repeatable

consumer-oriented trials that put LED

grow lights up against their HID

counterparts in conditions that

resemble a hobbyist indoor garden

room Until that happens individual

gardeners can experiment with LED grow lights on their own either on a small scale or by segregating a small number of plants within their garden for trials

Looking Ahead

What is the future of LED grow lights Near-term we should expect to see a wider variety of

LED grow lights coming onto the market These lights will increasingly include higher output

LEDs in a variety of light colors and configurations We expect to see combination lights

hitting the market using LED plus T5 fluorescent or HID garden lights to provide a more balanced spectrum than available from these garden lights used alone

We are starting to see LED grow lights designed to support different plant growth stages

such as grow and bloom and should expect lights to be introduced for specific plants such

as tomatoes herbs or orchids We will see continued improvements in light output

particularly as fourth-generation LEDs continue their migration from the lab to the market

Prices will begin to come down when sales volume increases

In the long run LED lighting could

obsolete almost every other type of

lighting Retrofit LED lamps that fit

into standard fluorescent lighting

fixtures are already available and

LED fixtures are in the works that

will replace street lights stadium

lights and other interior and

exterior lights Already Amsterdam

and Rotterdam in the Netherlands

are testing LED street lighting and

press reports indicate that other

major cities are considering similar trials

LED grow lights will be swept ahead

with the tide of mostly government-

funded research and development

currently underway Research

dollars invested by NASA and other

government agencies around the

globe are fueling tremendous

advances in LED lighting

technologies The energy saving

potential of LED lights is something

these entities cannot ignore if we

can find a way to consume less

energy to light up public and

private spaces we may be able to

postpone or scratch plans to build

new power plants or buy time until we are able to commercialize sustainable methods to generate and transport electricity

There is a lot of promise associated with LED grow lights but there are also unanswered

questions and unresolved debates The products that are available today should produce an

acceptable result so long as the gardener makes appropriate changes to their gardening

methods Wersquore looking forward to further articles and reports that describe how LED grow

lights perform against standard MH and HPS grow lights Wersquore hopeful about how LED grow

lights will fare in such comparisons

LED Growing Lights

Grow more plants with less electricity

Are LED growing lights better than fluorescent metal halide or high pressure sodium grow

lights Will they improve plant growth and will they use less electricity Is growing plants with LED growing lights environmentally friendly

Plants dont use the full visible spectrum to photosynthecize They predominantly use cool

(violet-blue and blue) and warm (orange-red) wavelengths which is a reflection of the

typical colors of natural night on a seasonal basis In the summer months when the sun is

more directly overhead cool colors predominate and tend to encourage healthy vegetative

growth while in spring and fall warm colors take over and tend to encourage flowering and fruiting

A typical metal halide grow light puts out much of its output in wavelength ranges that

plants do not use - cyan green yellow - and very little in the violet or blue regions So with

a metal halide grow light you are typically wasting much of the light shining down on your

plants A daylight metal halide light is more in the blue spectrum and so is useful for the

vegetative stage of growth but not for flowering or fruiting High pressure sodium lights

tend more to the warm red end of the spectrum and so are chiefly useful for flowering and fruiting

You can create your own LED growing lights by combining red and blue LED lights in roughly

a two- to-one proportion (two blue to one red) or buy an LED set designed specifically for

indoor growing which has blue and red LED grow lights in an appropriate proportion LED

grow lights have the benefit of low heat output so you dont need to worry about drying out

the soil or scorching the plants and they use very little electricity For example GlowPanel

LED growing lights cover a 15 square foot area (they are roughly 15 inches on a side) and

consume just 14 watts For growing purposes this light would be suitable for starting

seedlings or for growing herbs or lettuce indoors but is at the lower end of required light output for growing vegetables

Is it green to use LED growing lights Well its definitely an improvement to switch from

any of the other technologies as the amount of electricity youll use for the same amount of

growth is reduced significantly because of the concentration of light in the desired ranges of

the spectrum and because of the improved efficiency of LEDs But in absolute terms I

personally feel that LED growing lights should be used sparingly unless you have a source of carbon-neutral electricity that no one else has a use for

Why Lets consider a 6-square-foot herb garden using the GlowPanel LED growing lights

These lights consume 14 watts each for 15 square feet or 56 watts for the 6-square foot

garden The lights should be on about 12-16 hours a day for growing herbs or lettuce Lets

assume 12 hours to be conservative That meas were using 12 x 56 watts per day or 672 watt-hours Over a three month period that becomes about 60 kilowatt hours

Lets assume that 6-square foot garden produces 12 healthy heads of lettuce over the three

month period Each head of lettuce has therefore cost you 5 kilowatt hours of electricity

and might weigh a pound wet weight - and at about 95 water content would consist of less than an ounce of dried organic matter

and the transpiration rate of our plants Nutrient and water consumption go up as do the

required flow rates and reliability of our irrigation systems Just about every garden system

is significantly impacted by the waste heat from HID lights

What to do Itrsquos not like we can just turn off our grow lights and wait for something better

T5 fluorescent grow lights are energy efficient and cool running but their lower light output

makes them appropriate for plants that need less light such as leafy greens and foliage

plants At present only an HID garden light can put out enough light to provide a bountiful

harvest in plants that produce large fruit and flowers

The Promise of LED Grow Lights

Wersquove been waiting a long time for garden lights based on light-emitting diodes (LEDs) to

make it to ldquoprime timerdquo NASA and others have been experimenting with LED grow lights

since the mid-80rsquos and we are finally starting to see products reaching the market that reflect their findings These lights represent a major step forward

LED grow lights offer the dual benefit of low energy consumption and low heat generation

Some LED grow lights use so little electricity that they can be powered by a small solar

panel According to their manufacturers todayrsquos LED grow lights consume between 2 and

50 of the electricity used by the HID grow lights they reportedly replace Wersquove yet to see

in real-world application whether these lights will perform as well in the garden as those

ldquocomparablerdquo HIDs particularly for high-light crops

LEDs short for Light Emitting Diodes

are tiny semiconductor chips that

generate light when electrified It takes

a small amount of electricity to make

an LED glow (emit electrons) and the

elements that the diode is made from

determine the light spectrum it emits

An LED is backed by an internal

reflector and encased in an epoxy body

with an integrated lens Together

these components determine the angle

of the light emitted by the diode which

is shaped as a downward-facing cone

Individual LEDs produce relatively

small light cones so they are clustered

into arrays so the light cones overlap

increasing light intensity and coverage

area

LED grow lights are designed to

stimulate photosynthesis by providing light in the frequencies that plants primarily use for

this critical biological process Individual LEDs may contain one of 29 known combinations of

elements that emit light in different colors when excited by electrons Grow light

manufacturers emphasize blue and red LEDs in their fixtures sometimes with other colors

which gives many LED grow lights their distinctive purplish-red color Optimizing the light

spectrum helps in two ways it enhances photosynthesis and saves energy by not generating light in colors that plants do not use

LED Cost Savings

LED grow lights have a longer useful life

than MH or HPS lights as long as 15 years

for some fixtures and thus a lower ldquototal

cost of ownershiprdquo The total cost of

ownership includes the cost to buy the

light use it and replace expired bulbs

One manufacturer estimates that the total

cost of owning an LED grow light over five

years is about half the cost of a

comparable HPS light based on an

analysis that balances the upfront cost to

purchase an LED grow light against lower

electrical costs and eliminating the need

to periodically replace bulbs Their

analysis used an electric rate of $007 per

kilowatt hour ndash here in Southern California

where electric rates are twice as high the

total cost difference between an LED grow

light and a MH or HPS light would be even greater

You may also be able to save space or

move into a smaller space with LED grow

lights There is no need for bulky

reflectors and ventilationcooling

equipment such as fans air conditioners

and ductwork may be eliminated or scaled back The room will also be significantly quieter with fewer noisy fans ballasts and chillers

Thus the promise of LED grow lights has five aspects lower energy consumption lower

heat emissions customizable photosynthetic spectrum lower total cost of ownership and

smaller garden space requirements Can todayrsquos LED grow lights actually deliver these

benefits The answer to that question depends on who you ask Before we get to those

questions however letrsquos take a step back and examine light and photosynthesis a little more closely

Electromagnetic Spectrum and Photosynthesis

Electromagnetic radiation spans a broad range of wavelengths which includes what we

recognize as ldquovisible lightrdquo At the one end of the electromagnetic spectrum are gamma

rays which have a wavelength of 5-10 nanometers (nm) A nanometer is one-billionth of a

meter a very small measure indeed At the other end of the electromagnetic spectrum are

radio waves with a wavelength of 1012 nm Smack in the middle are the wavelengths that

can be seen by the human eye that fall between 380 and 750 nm This part of the

electromagnetic spectrum is what we call ldquovisible lightrdquo

Plants use visible light differently than we do Their leaves contain chlorophyll a compound

vital for photosynthesis the process by which plants convert light into fuel Chlorophyll

molecules are highly selective about the light they absorb blue light primarily in the 460-

480 nm range and red light around 640-680 nm Chlorophyll for the most part reflects

instead of absorbs most green and yellow light which is why plants appear green to our

eyes

Limiting any grow light to just red and blue light would lead to poor results since plants

also use most of rest of the visible spectrum though in lower amounts NASArsquos Biological

Sciences team at the Kennedy Space Center has done extensive research on this subject a

2006 paper published by the International Society of Horticultural Science documented

improvements in lettuce yields when 24 green light was added to LED grow lights that

otherwise produced only red and blue light Including light in the yellow-green spectrum

also helps to visually restore green color to plants making them look more ldquonormalrdquo and

makes it easier to identify garden problems such as nutrient deficiencies or pest attacks

This combination also makes it easier for gardeners to work in their gardens

Increasing the amount of red and blue light reaching the garden isnrsquot an idea limited to LED

grow lights Enhanced-spectrum MH and HPS bulbs such as Hortilux and SolarMax lamps

provide more blue and red light than standard bulbs So water-cooled HID lights according

to their manufacturers Enhanced-spectrum and water-cooled HID lights still put out a lot of

light in yellow-green wavelengths too that look bright to the human eye but donrsquot do much

for our plants An LED grow light designer isnrsquot trying to reproduce sunlight or make up for

the spectral shortcomings of a light originally designed for another purpose Instead they

are trying to create optimal light output for photosynthesis

Current state of the art

So do todayrsquos LED grow lights live up to expectations

Energy consumption is significantly lower for LED lights vs ldquoequivalentrdquo HID lights Most

grow light manufacturers are working to replace the light output of a 400-500 watt HID light

with between 30 and 300 watts of power consumed and some go quite a lot lower The

juryrsquos still out on how these lights truly compare to their HID cousins on garden performance and yield but on the energy promise they seem to perform well

The lights fare well on the heat promise too Most LED grow lights put out very little heat

so do not have any specific cooling requirements A lightrsquos heat output is affected by its

design some lights cluster LEDs in round or square ldquopodsrdquo or ldquorosettesrdquo that are spaced

along horizontal bars These designs help to limit heat accumulation by spacing the LEDs

farther apart Other lights bunch the LEDs close together in a single fixture to provide a

greater light intensity directly below the light These designs can accumulate heat so

generally incorporate heat management features such as heat shielding fans for air cooling

or water cooling

The third promise customized light spectrum is a topic where debates swirl Skeptics do

not believe LEDs can ever produce light that is intense enough to be effective for

photosynthesis no matter what color it is These concerns are based on earlier generation

LEDs that did not put out enough energy to work well as grow lights Todayrsquos ldquothird

generationrdquo LEDs reportedly solve this problem by putting out up to three watts of light

energy per LED a 20-50 fold improvement over second-generation LEDs New-generation

LEDs also have a wider ldquobeam anglerdquo that permits an LED to project light across a 120

degree arc instead of mostly just straight down (ldquopin pointrdquo lighting) This means wider light cones improving light intensity and coverage at the garden canopy

Passionate debates about LED grow light design and effectiveness are waged on a regular

basis in online gardening communities Some posts describe LED grow light trials people are

conducting in their homes While these posts are interesting reading and therersquos a lot to be

learned from them they should also be taken with a grain of salt Many hobbyists want to

debate whether LED grow lights are or can be effective The academic and scientific

communities satisfied for some time that LED grow lights are effective have moved on to

figuring out ldquohowrdquo

Updating Garden Methods for LEDs

One point that LED grow light manufacturers emphasize is that we must update our

gardening methods to use LED grow lights to their best advantage Using an LED grow light

without changing gardening methods will likely result in a disappointing outcome The first

caution is to not overwater Yoursquove eliminated one of the largest sources of heat in your

garden your HID garden lights

With less heat your plants consume less nutrient solution and less of it evaporates thus

less solution is needed One lighting manufacturer also suggests using a weaker nutrient

solution to match lower plant transpiration rates Less solution and less nutrients used this

should be good news right Yes and no Reservoirs can be smaller saving money and

space Fewer expensive bottles of hydroponic nutrient solutions are needed

The dark side is subtle but compelling the most

frequent cause of indoor plant death is

overwatering Itrsquos just as true for plants in a fully

automated indoor garden as it is for an African

violet on the kitchen windowsill Those accustomed

to gardening under HID lights will find that itrsquos

extremely easy to overwater under LED grow

lights Your plants simply need less water when there is less heat

Overwatering can lead to root rot or drowning if itrsquos

not caught and corrected right away When using

LED grow lights be sure to select a porous growing

media to provide adequate drainage and plenty of

air space in the root zone Also let your plants

almost dry more between feedings Overwatering

can also increase garden humidity levels which

can promote the development of fungus and other

garden ills Keep a close watch on growing media

moisture levels and garden relative humidity when

using LED grow lights An LED grow light that emits

some UV-A spectrum (invisible but felt as heat)

may help to kill or retard mildew Maintaining constant air movement within the garden

using oscillating or fixed fans will also help to keep mold and mildew in check

Grow light manufacturers also recommend supplementing the garden atmosphere with

carbon dioxide (CO2) While supplemental CO2 will improve the yield of any garden when

properly applied there are two particular benefits when using CO2 with LED grow lights

First even though an LED grow light may look dim to the human eye it is putting out a lot

of light energy in the spectrum needed for photosynthesis ndash ideally more than the plants

would receive under ldquocomparablerdquo MH or HPS lights Plants need higher CO2 levels in order

to turn this additional light into fuel The second benefit is that with lower heat output there

is less need to vent or air condition the garden space Itrsquos easier to seal the garden environment for CO2 when itrsquos not as hot

Top Two Concerns

We asked several LED lighting manufacturers about the concerns customers express when

considering an LED grow light Two primary concerns emerged

The first is the price for LED grow lights LED grow lights can be purchased on eBay for as

little as $9 for a screw-in replacement grow bulb to as much as $1500 for a water-cooled

garden light fixture reported to be equivalent to a 400- to 500 watt HPS light Donrsquot be

misled by the low price on some of the LED lights on eBay ndash they often include lower-

output inferior LEDs and some of them are recycled traffic signal lights A large number of

these inexpensive LED ldquogrow lightsrdquo may be needed to provide illumination for a standard-

sized hobby garden buyer beware A home gardener should expect to spend between $500

and $1500 for LED grow lights to illuminate a 3rsquo x 3rsquo growing space The ldquototal cost of

ownershiprdquo models discussed earlier are one way to understand the price issue LED grow

lights require a larger up-front investment which should be more than offset by reduced operating costs going forward

The second concern is that nobody

wants to go first More people are

interested in LED grow lights than are

ready to start using them Gardeners

do not want their crop to wind up as

the ldquoguinea pigrdquo in a failed garden

lighting experiment A lot of trials and

research have been conducted in

research laboratories that show LED

grow lights to be effective and cost-

efficient But those trials were done in

a laboratory setting Whatrsquos missing

are verifiable and repeatable

consumer-oriented trials that put LED

grow lights up against their HID

counterparts in conditions that

resemble a hobbyist indoor garden

room Until that happens individual

gardeners can experiment with LED grow lights on their own either on a small scale or by segregating a small number of plants within their garden for trials

Looking Ahead

What is the future of LED grow lights Near-term we should expect to see a wider variety of

LED grow lights coming onto the market These lights will increasingly include higher output

LEDs in a variety of light colors and configurations We expect to see combination lights

hitting the market using LED plus T5 fluorescent or HID garden lights to provide a more balanced spectrum than available from these garden lights used alone

We are starting to see LED grow lights designed to support different plant growth stages

such as grow and bloom and should expect lights to be introduced for specific plants such

as tomatoes herbs or orchids We will see continued improvements in light output

particularly as fourth-generation LEDs continue their migration from the lab to the market

Prices will begin to come down when sales volume increases

In the long run LED lighting could

obsolete almost every other type of

lighting Retrofit LED lamps that fit

into standard fluorescent lighting

fixtures are already available and

LED fixtures are in the works that

will replace street lights stadium

lights and other interior and

exterior lights Already Amsterdam

and Rotterdam in the Netherlands

are testing LED street lighting and

press reports indicate that other

major cities are considering similar trials

LED grow lights will be swept ahead

with the tide of mostly government-

funded research and development

currently underway Research

dollars invested by NASA and other

government agencies around the

globe are fueling tremendous

advances in LED lighting

technologies The energy saving

potential of LED lights is something

these entities cannot ignore if we

can find a way to consume less

energy to light up public and

private spaces we may be able to

postpone or scratch plans to build

new power plants or buy time until we are able to commercialize sustainable methods to generate and transport electricity

There is a lot of promise associated with LED grow lights but there are also unanswered

questions and unresolved debates The products that are available today should produce an

acceptable result so long as the gardener makes appropriate changes to their gardening

methods Wersquore looking forward to further articles and reports that describe how LED grow

lights perform against standard MH and HPS grow lights Wersquore hopeful about how LED grow

lights will fare in such comparisons

LED Growing Lights

Grow more plants with less electricity

Are LED growing lights better than fluorescent metal halide or high pressure sodium grow

lights Will they improve plant growth and will they use less electricity Is growing plants with LED growing lights environmentally friendly

Plants dont use the full visible spectrum to photosynthecize They predominantly use cool

(violet-blue and blue) and warm (orange-red) wavelengths which is a reflection of the

typical colors of natural night on a seasonal basis In the summer months when the sun is

more directly overhead cool colors predominate and tend to encourage healthy vegetative

growth while in spring and fall warm colors take over and tend to encourage flowering and fruiting

A typical metal halide grow light puts out much of its output in wavelength ranges that

plants do not use - cyan green yellow - and very little in the violet or blue regions So with

a metal halide grow light you are typically wasting much of the light shining down on your

plants A daylight metal halide light is more in the blue spectrum and so is useful for the

vegetative stage of growth but not for flowering or fruiting High pressure sodium lights

tend more to the warm red end of the spectrum and so are chiefly useful for flowering and fruiting

You can create your own LED growing lights by combining red and blue LED lights in roughly

a two- to-one proportion (two blue to one red) or buy an LED set designed specifically for

indoor growing which has blue and red LED grow lights in an appropriate proportion LED

grow lights have the benefit of low heat output so you dont need to worry about drying out

the soil or scorching the plants and they use very little electricity For example GlowPanel

LED growing lights cover a 15 square foot area (they are roughly 15 inches on a side) and

consume just 14 watts For growing purposes this light would be suitable for starting

seedlings or for growing herbs or lettuce indoors but is at the lower end of required light output for growing vegetables

Is it green to use LED growing lights Well its definitely an improvement to switch from

any of the other technologies as the amount of electricity youll use for the same amount of

growth is reduced significantly because of the concentration of light in the desired ranges of

the spectrum and because of the improved efficiency of LEDs But in absolute terms I

personally feel that LED growing lights should be used sparingly unless you have a source of carbon-neutral electricity that no one else has a use for

Why Lets consider a 6-square-foot herb garden using the GlowPanel LED growing lights

These lights consume 14 watts each for 15 square feet or 56 watts for the 6-square foot

garden The lights should be on about 12-16 hours a day for growing herbs or lettuce Lets

assume 12 hours to be conservative That meas were using 12 x 56 watts per day or 672 watt-hours Over a three month period that becomes about 60 kilowatt hours

Lets assume that 6-square foot garden produces 12 healthy heads of lettuce over the three

month period Each head of lettuce has therefore cost you 5 kilowatt hours of electricity

and might weigh a pound wet weight - and at about 95 water content would consist of less than an ounce of dried organic matter

LED Cost Savings

LED grow lights have a longer useful life

than MH or HPS lights as long as 15 years

for some fixtures and thus a lower ldquototal

cost of ownershiprdquo The total cost of

ownership includes the cost to buy the

light use it and replace expired bulbs

One manufacturer estimates that the total

cost of owning an LED grow light over five

years is about half the cost of a

comparable HPS light based on an

analysis that balances the upfront cost to

purchase an LED grow light against lower

electrical costs and eliminating the need

to periodically replace bulbs Their

analysis used an electric rate of $007 per

kilowatt hour ndash here in Southern California

where electric rates are twice as high the

total cost difference between an LED grow

light and a MH or HPS light would be even greater

You may also be able to save space or

move into a smaller space with LED grow

lights There is no need for bulky

reflectors and ventilationcooling

equipment such as fans air conditioners

and ductwork may be eliminated or scaled back The room will also be significantly quieter with fewer noisy fans ballasts and chillers

Thus the promise of LED grow lights has five aspects lower energy consumption lower

heat emissions customizable photosynthetic spectrum lower total cost of ownership and

smaller garden space requirements Can todayrsquos LED grow lights actually deliver these

benefits The answer to that question depends on who you ask Before we get to those

questions however letrsquos take a step back and examine light and photosynthesis a little more closely

Electromagnetic Spectrum and Photosynthesis

Electromagnetic radiation spans a broad range of wavelengths which includes what we

recognize as ldquovisible lightrdquo At the one end of the electromagnetic spectrum are gamma

rays which have a wavelength of 5-10 nanometers (nm) A nanometer is one-billionth of a

meter a very small measure indeed At the other end of the electromagnetic spectrum are

radio waves with a wavelength of 1012 nm Smack in the middle are the wavelengths that

can be seen by the human eye that fall between 380 and 750 nm This part of the

electromagnetic spectrum is what we call ldquovisible lightrdquo

Plants use visible light differently than we do Their leaves contain chlorophyll a compound

vital for photosynthesis the process by which plants convert light into fuel Chlorophyll

molecules are highly selective about the light they absorb blue light primarily in the 460-

480 nm range and red light around 640-680 nm Chlorophyll for the most part reflects

instead of absorbs most green and yellow light which is why plants appear green to our

eyes

Limiting any grow light to just red and blue light would lead to poor results since plants

also use most of rest of the visible spectrum though in lower amounts NASArsquos Biological

Sciences team at the Kennedy Space Center has done extensive research on this subject a

2006 paper published by the International Society of Horticultural Science documented

improvements in lettuce yields when 24 green light was added to LED grow lights that

otherwise produced only red and blue light Including light in the yellow-green spectrum

also helps to visually restore green color to plants making them look more ldquonormalrdquo and

makes it easier to identify garden problems such as nutrient deficiencies or pest attacks

This combination also makes it easier for gardeners to work in their gardens

Increasing the amount of red and blue light reaching the garden isnrsquot an idea limited to LED

grow lights Enhanced-spectrum MH and HPS bulbs such as Hortilux and SolarMax lamps

provide more blue and red light than standard bulbs So water-cooled HID lights according

to their manufacturers Enhanced-spectrum and water-cooled HID lights still put out a lot of

light in yellow-green wavelengths too that look bright to the human eye but donrsquot do much

for our plants An LED grow light designer isnrsquot trying to reproduce sunlight or make up for

the spectral shortcomings of a light originally designed for another purpose Instead they

are trying to create optimal light output for photosynthesis

Current state of the art

So do todayrsquos LED grow lights live up to expectations

Energy consumption is significantly lower for LED lights vs ldquoequivalentrdquo HID lights Most

grow light manufacturers are working to replace the light output of a 400-500 watt HID light

with between 30 and 300 watts of power consumed and some go quite a lot lower The

juryrsquos still out on how these lights truly compare to their HID cousins on garden performance and yield but on the energy promise they seem to perform well

The lights fare well on the heat promise too Most LED grow lights put out very little heat

so do not have any specific cooling requirements A lightrsquos heat output is affected by its

design some lights cluster LEDs in round or square ldquopodsrdquo or ldquorosettesrdquo that are spaced

along horizontal bars These designs help to limit heat accumulation by spacing the LEDs

farther apart Other lights bunch the LEDs close together in a single fixture to provide a

greater light intensity directly below the light These designs can accumulate heat so

generally incorporate heat management features such as heat shielding fans for air cooling

or water cooling

The third promise customized light spectrum is a topic where debates swirl Skeptics do

not believe LEDs can ever produce light that is intense enough to be effective for

photosynthesis no matter what color it is These concerns are based on earlier generation

LEDs that did not put out enough energy to work well as grow lights Todayrsquos ldquothird

generationrdquo LEDs reportedly solve this problem by putting out up to three watts of light

energy per LED a 20-50 fold improvement over second-generation LEDs New-generation

LEDs also have a wider ldquobeam anglerdquo that permits an LED to project light across a 120

degree arc instead of mostly just straight down (ldquopin pointrdquo lighting) This means wider light cones improving light intensity and coverage at the garden canopy

Passionate debates about LED grow light design and effectiveness are waged on a regular

basis in online gardening communities Some posts describe LED grow light trials people are

conducting in their homes While these posts are interesting reading and therersquos a lot to be

learned from them they should also be taken with a grain of salt Many hobbyists want to

debate whether LED grow lights are or can be effective The academic and scientific

communities satisfied for some time that LED grow lights are effective have moved on to

figuring out ldquohowrdquo

Updating Garden Methods for LEDs

One point that LED grow light manufacturers emphasize is that we must update our

gardening methods to use LED grow lights to their best advantage Using an LED grow light

without changing gardening methods will likely result in a disappointing outcome The first

caution is to not overwater Yoursquove eliminated one of the largest sources of heat in your

garden your HID garden lights

With less heat your plants consume less nutrient solution and less of it evaporates thus

less solution is needed One lighting manufacturer also suggests using a weaker nutrient

solution to match lower plant transpiration rates Less solution and less nutrients used this

should be good news right Yes and no Reservoirs can be smaller saving money and

space Fewer expensive bottles of hydroponic nutrient solutions are needed

The dark side is subtle but compelling the most

frequent cause of indoor plant death is

overwatering Itrsquos just as true for plants in a fully

automated indoor garden as it is for an African

violet on the kitchen windowsill Those accustomed

to gardening under HID lights will find that itrsquos

extremely easy to overwater under LED grow

lights Your plants simply need less water when there is less heat

Overwatering can lead to root rot or drowning if itrsquos

not caught and corrected right away When using

LED grow lights be sure to select a porous growing

media to provide adequate drainage and plenty of

air space in the root zone Also let your plants

almost dry more between feedings Overwatering

can also increase garden humidity levels which

can promote the development of fungus and other

garden ills Keep a close watch on growing media

moisture levels and garden relative humidity when

using LED grow lights An LED grow light that emits

some UV-A spectrum (invisible but felt as heat)

may help to kill or retard mildew Maintaining constant air movement within the garden

using oscillating or fixed fans will also help to keep mold and mildew in check

Grow light manufacturers also recommend supplementing the garden atmosphere with

carbon dioxide (CO2) While supplemental CO2 will improve the yield of any garden when

properly applied there are two particular benefits when using CO2 with LED grow lights

First even though an LED grow light may look dim to the human eye it is putting out a lot

of light energy in the spectrum needed for photosynthesis ndash ideally more than the plants

would receive under ldquocomparablerdquo MH or HPS lights Plants need higher CO2 levels in order

to turn this additional light into fuel The second benefit is that with lower heat output there

is less need to vent or air condition the garden space Itrsquos easier to seal the garden environment for CO2 when itrsquos not as hot

Top Two Concerns

We asked several LED lighting manufacturers about the concerns customers express when

considering an LED grow light Two primary concerns emerged

The first is the price for LED grow lights LED grow lights can be purchased on eBay for as

little as $9 for a screw-in replacement grow bulb to as much as $1500 for a water-cooled

garden light fixture reported to be equivalent to a 400- to 500 watt HPS light Donrsquot be

misled by the low price on some of the LED lights on eBay ndash they often include lower-

output inferior LEDs and some of them are recycled traffic signal lights A large number of

these inexpensive LED ldquogrow lightsrdquo may be needed to provide illumination for a standard-

sized hobby garden buyer beware A home gardener should expect to spend between $500

and $1500 for LED grow lights to illuminate a 3rsquo x 3rsquo growing space The ldquototal cost of

ownershiprdquo models discussed earlier are one way to understand the price issue LED grow

lights require a larger up-front investment which should be more than offset by reduced operating costs going forward

The second concern is that nobody

wants to go first More people are

interested in LED grow lights than are

ready to start using them Gardeners

do not want their crop to wind up as

the ldquoguinea pigrdquo in a failed garden

lighting experiment A lot of trials and

research have been conducted in

research laboratories that show LED

grow lights to be effective and cost-

efficient But those trials were done in

a laboratory setting Whatrsquos missing

are verifiable and repeatable

consumer-oriented trials that put LED

grow lights up against their HID

counterparts in conditions that

resemble a hobbyist indoor garden

room Until that happens individual

gardeners can experiment with LED grow lights on their own either on a small scale or by segregating a small number of plants within their garden for trials

Looking Ahead

What is the future of LED grow lights Near-term we should expect to see a wider variety of

LED grow lights coming onto the market These lights will increasingly include higher output

LEDs in a variety of light colors and configurations We expect to see combination lights

hitting the market using LED plus T5 fluorescent or HID garden lights to provide a more balanced spectrum than available from these garden lights used alone

We are starting to see LED grow lights designed to support different plant growth stages

such as grow and bloom and should expect lights to be introduced for specific plants such

as tomatoes herbs or orchids We will see continued improvements in light output

particularly as fourth-generation LEDs continue their migration from the lab to the market

Prices will begin to come down when sales volume increases

In the long run LED lighting could

obsolete almost every other type of

lighting Retrofit LED lamps that fit

into standard fluorescent lighting

fixtures are already available and

LED fixtures are in the works that

will replace street lights stadium

lights and other interior and

exterior lights Already Amsterdam

and Rotterdam in the Netherlands

are testing LED street lighting and

press reports indicate that other

major cities are considering similar trials

LED grow lights will be swept ahead

with the tide of mostly government-

funded research and development

currently underway Research

dollars invested by NASA and other

government agencies around the

globe are fueling tremendous

advances in LED lighting

technologies The energy saving

potential of LED lights is something

these entities cannot ignore if we

can find a way to consume less

energy to light up public and

private spaces we may be able to

postpone or scratch plans to build

new power plants or buy time until we are able to commercialize sustainable methods to generate and transport electricity

There is a lot of promise associated with LED grow lights but there are also unanswered

questions and unresolved debates The products that are available today should produce an

acceptable result so long as the gardener makes appropriate changes to their gardening

methods Wersquore looking forward to further articles and reports that describe how LED grow

lights perform against standard MH and HPS grow lights Wersquore hopeful about how LED grow

lights will fare in such comparisons

LED Growing Lights

Grow more plants with less electricity

Are LED growing lights better than fluorescent metal halide or high pressure sodium grow

lights Will they improve plant growth and will they use less electricity Is growing plants with LED growing lights environmentally friendly

Plants dont use the full visible spectrum to photosynthecize They predominantly use cool

(violet-blue and blue) and warm (orange-red) wavelengths which is a reflection of the

typical colors of natural night on a seasonal basis In the summer months when the sun is

more directly overhead cool colors predominate and tend to encourage healthy vegetative

growth while in spring and fall warm colors take over and tend to encourage flowering and fruiting

A typical metal halide grow light puts out much of its output in wavelength ranges that

plants do not use - cyan green yellow - and very little in the violet or blue regions So with

a metal halide grow light you are typically wasting much of the light shining down on your

plants A daylight metal halide light is more in the blue spectrum and so is useful for the

vegetative stage of growth but not for flowering or fruiting High pressure sodium lights

tend more to the warm red end of the spectrum and so are chiefly useful for flowering and fruiting

You can create your own LED growing lights by combining red and blue LED lights in roughly

a two- to-one proportion (two blue to one red) or buy an LED set designed specifically for

indoor growing which has blue and red LED grow lights in an appropriate proportion LED

grow lights have the benefit of low heat output so you dont need to worry about drying out

the soil or scorching the plants and they use very little electricity For example GlowPanel

LED growing lights cover a 15 square foot area (they are roughly 15 inches on a side) and

consume just 14 watts For growing purposes this light would be suitable for starting

seedlings or for growing herbs or lettuce indoors but is at the lower end of required light output for growing vegetables

Is it green to use LED growing lights Well its definitely an improvement to switch from

any of the other technologies as the amount of electricity youll use for the same amount of

growth is reduced significantly because of the concentration of light in the desired ranges of

the spectrum and because of the improved efficiency of LEDs But in absolute terms I

personally feel that LED growing lights should be used sparingly unless you have a source of carbon-neutral electricity that no one else has a use for

Why Lets consider a 6-square-foot herb garden using the GlowPanel LED growing lights

These lights consume 14 watts each for 15 square feet or 56 watts for the 6-square foot

garden The lights should be on about 12-16 hours a day for growing herbs or lettuce Lets

assume 12 hours to be conservative That meas were using 12 x 56 watts per day or 672 watt-hours Over a three month period that becomes about 60 kilowatt hours

Lets assume that 6-square foot garden produces 12 healthy heads of lettuce over the three

month period Each head of lettuce has therefore cost you 5 kilowatt hours of electricity

and might weigh a pound wet weight - and at about 95 water content would consist of less than an ounce of dried organic matter

Plants use visible light differently than we do Their leaves contain chlorophyll a compound

vital for photosynthesis the process by which plants convert light into fuel Chlorophyll

molecules are highly selective about the light they absorb blue light primarily in the 460-

480 nm range and red light around 640-680 nm Chlorophyll for the most part reflects

instead of absorbs most green and yellow light which is why plants appear green to our

eyes

Limiting any grow light to just red and blue light would lead to poor results since plants

also use most of rest of the visible spectrum though in lower amounts NASArsquos Biological

Sciences team at the Kennedy Space Center has done extensive research on this subject a

2006 paper published by the International Society of Horticultural Science documented

improvements in lettuce yields when 24 green light was added to LED grow lights that

otherwise produced only red and blue light Including light in the yellow-green spectrum

also helps to visually restore green color to plants making them look more ldquonormalrdquo and

makes it easier to identify garden problems such as nutrient deficiencies or pest attacks

This combination also makes it easier for gardeners to work in their gardens

Increasing the amount of red and blue light reaching the garden isnrsquot an idea limited to LED

grow lights Enhanced-spectrum MH and HPS bulbs such as Hortilux and SolarMax lamps

provide more blue and red light than standard bulbs So water-cooled HID lights according

to their manufacturers Enhanced-spectrum and water-cooled HID lights still put out a lot of

light in yellow-green wavelengths too that look bright to the human eye but donrsquot do much

for our plants An LED grow light designer isnrsquot trying to reproduce sunlight or make up for

the spectral shortcomings of a light originally designed for another purpose Instead they

are trying to create optimal light output for photosynthesis

Current state of the art

So do todayrsquos LED grow lights live up to expectations

Energy consumption is significantly lower for LED lights vs ldquoequivalentrdquo HID lights Most

grow light manufacturers are working to replace the light output of a 400-500 watt HID light

with between 30 and 300 watts of power consumed and some go quite a lot lower The

juryrsquos still out on how these lights truly compare to their HID cousins on garden performance and yield but on the energy promise they seem to perform well

The lights fare well on the heat promise too Most LED grow lights put out very little heat

so do not have any specific cooling requirements A lightrsquos heat output is affected by its

design some lights cluster LEDs in round or square ldquopodsrdquo or ldquorosettesrdquo that are spaced

along horizontal bars These designs help to limit heat accumulation by spacing the LEDs

farther apart Other lights bunch the LEDs close together in a single fixture to provide a

greater light intensity directly below the light These designs can accumulate heat so

generally incorporate heat management features such as heat shielding fans for air cooling

or water cooling

The third promise customized light spectrum is a topic where debates swirl Skeptics do

not believe LEDs can ever produce light that is intense enough to be effective for

photosynthesis no matter what color it is These concerns are based on earlier generation

LEDs that did not put out enough energy to work well as grow lights Todayrsquos ldquothird

generationrdquo LEDs reportedly solve this problem by putting out up to three watts of light

energy per LED a 20-50 fold improvement over second-generation LEDs New-generation

LEDs also have a wider ldquobeam anglerdquo that permits an LED to project light across a 120

degree arc instead of mostly just straight down (ldquopin pointrdquo lighting) This means wider light cones improving light intensity and coverage at the garden canopy

Passionate debates about LED grow light design and effectiveness are waged on a regular

basis in online gardening communities Some posts describe LED grow light trials people are

conducting in their homes While these posts are interesting reading and therersquos a lot to be

learned from them they should also be taken with a grain of salt Many hobbyists want to

debate whether LED grow lights are or can be effective The academic and scientific

communities satisfied for some time that LED grow lights are effective have moved on to

figuring out ldquohowrdquo

Updating Garden Methods for LEDs

One point that LED grow light manufacturers emphasize is that we must update our

gardening methods to use LED grow lights to their best advantage Using an LED grow light

without changing gardening methods will likely result in a disappointing outcome The first

caution is to not overwater Yoursquove eliminated one of the largest sources of heat in your

garden your HID garden lights

With less heat your plants consume less nutrient solution and less of it evaporates thus

less solution is needed One lighting manufacturer also suggests using a weaker nutrient

solution to match lower plant transpiration rates Less solution and less nutrients used this

should be good news right Yes and no Reservoirs can be smaller saving money and

space Fewer expensive bottles of hydroponic nutrient solutions are needed

The dark side is subtle but compelling the most

frequent cause of indoor plant death is

overwatering Itrsquos just as true for plants in a fully

automated indoor garden as it is for an African

violet on the kitchen windowsill Those accustomed

to gardening under HID lights will find that itrsquos

extremely easy to overwater under LED grow

lights Your plants simply need less water when there is less heat

Overwatering can lead to root rot or drowning if itrsquos

not caught and corrected right away When using

LED grow lights be sure to select a porous growing

media to provide adequate drainage and plenty of

air space in the root zone Also let your plants

almost dry more between feedings Overwatering

can also increase garden humidity levels which

can promote the development of fungus and other

garden ills Keep a close watch on growing media

moisture levels and garden relative humidity when

using LED grow lights An LED grow light that emits

some UV-A spectrum (invisible but felt as heat)

may help to kill or retard mildew Maintaining constant air movement within the garden

using oscillating or fixed fans will also help to keep mold and mildew in check

Grow light manufacturers also recommend supplementing the garden atmosphere with

carbon dioxide (CO2) While supplemental CO2 will improve the yield of any garden when

properly applied there are two particular benefits when using CO2 with LED grow lights

First even though an LED grow light may look dim to the human eye it is putting out a lot

of light energy in the spectrum needed for photosynthesis ndash ideally more than the plants

would receive under ldquocomparablerdquo MH or HPS lights Plants need higher CO2 levels in order

to turn this additional light into fuel The second benefit is that with lower heat output there

is less need to vent or air condition the garden space Itrsquos easier to seal the garden environment for CO2 when itrsquos not as hot

Top Two Concerns

We asked several LED lighting manufacturers about the concerns customers express when

considering an LED grow light Two primary concerns emerged

The first is the price for LED grow lights LED grow lights can be purchased on eBay for as

little as $9 for a screw-in replacement grow bulb to as much as $1500 for a water-cooled

garden light fixture reported to be equivalent to a 400- to 500 watt HPS light Donrsquot be

misled by the low price on some of the LED lights on eBay ndash they often include lower-

output inferior LEDs and some of them are recycled traffic signal lights A large number of

these inexpensive LED ldquogrow lightsrdquo may be needed to provide illumination for a standard-

sized hobby garden buyer beware A home gardener should expect to spend between $500

and $1500 for LED grow lights to illuminate a 3rsquo x 3rsquo growing space The ldquototal cost of

ownershiprdquo models discussed earlier are one way to understand the price issue LED grow

lights require a larger up-front investment which should be more than offset by reduced operating costs going forward

The second concern is that nobody

wants to go first More people are

interested in LED grow lights than are

ready to start using them Gardeners

do not want their crop to wind up as

the ldquoguinea pigrdquo in a failed garden

lighting experiment A lot of trials and

research have been conducted in

research laboratories that show LED

grow lights to be effective and cost-

efficient But those trials were done in

a laboratory setting Whatrsquos missing

are verifiable and repeatable

consumer-oriented trials that put LED

grow lights up against their HID

counterparts in conditions that

resemble a hobbyist indoor garden

room Until that happens individual

gardeners can experiment with LED grow lights on their own either on a small scale or by segregating a small number of plants within their garden for trials

Looking Ahead

What is the future of LED grow lights Near-term we should expect to see a wider variety of

LED grow lights coming onto the market These lights will increasingly include higher output

LEDs in a variety of light colors and configurations We expect to see combination lights

hitting the market using LED plus T5 fluorescent or HID garden lights to provide a more balanced spectrum than available from these garden lights used alone

We are starting to see LED grow lights designed to support different plant growth stages

such as grow and bloom and should expect lights to be introduced for specific plants such

as tomatoes herbs or orchids We will see continued improvements in light output

particularly as fourth-generation LEDs continue their migration from the lab to the market

Prices will begin to come down when sales volume increases

In the long run LED lighting could

obsolete almost every other type of

lighting Retrofit LED lamps that fit

into standard fluorescent lighting

fixtures are already available and

LED fixtures are in the works that

will replace street lights stadium

lights and other interior and

exterior lights Already Amsterdam

and Rotterdam in the Netherlands

are testing LED street lighting and

press reports indicate that other

major cities are considering similar trials

LED grow lights will be swept ahead

with the tide of mostly government-

funded research and development

currently underway Research

dollars invested by NASA and other

government agencies around the

globe are fueling tremendous

advances in LED lighting

technologies The energy saving

potential of LED lights is something

these entities cannot ignore if we

can find a way to consume less

energy to light up public and

private spaces we may be able to

postpone or scratch plans to build

new power plants or buy time until we are able to commercialize sustainable methods to generate and transport electricity

There is a lot of promise associated with LED grow lights but there are also unanswered

questions and unresolved debates The products that are available today should produce an

acceptable result so long as the gardener makes appropriate changes to their gardening

methods Wersquore looking forward to further articles and reports that describe how LED grow

lights perform against standard MH and HPS grow lights Wersquore hopeful about how LED grow

lights will fare in such comparisons

LED Growing Lights

Grow more plants with less electricity

Are LED growing lights better than fluorescent metal halide or high pressure sodium grow

lights Will they improve plant growth and will they use less electricity Is growing plants with LED growing lights environmentally friendly

Plants dont use the full visible spectrum to photosynthecize They predominantly use cool

(violet-blue and blue) and warm (orange-red) wavelengths which is a reflection of the

typical colors of natural night on a seasonal basis In the summer months when the sun is

more directly overhead cool colors predominate and tend to encourage healthy vegetative

growth while in spring and fall warm colors take over and tend to encourage flowering and fruiting

A typical metal halide grow light puts out much of its output in wavelength ranges that

plants do not use - cyan green yellow - and very little in the violet or blue regions So with

a metal halide grow light you are typically wasting much of the light shining down on your

plants A daylight metal halide light is more in the blue spectrum and so is useful for the

vegetative stage of growth but not for flowering or fruiting High pressure sodium lights

tend more to the warm red end of the spectrum and so are chiefly useful for flowering and fruiting

You can create your own LED growing lights by combining red and blue LED lights in roughly

a two- to-one proportion (two blue to one red) or buy an LED set designed specifically for

indoor growing which has blue and red LED grow lights in an appropriate proportion LED

grow lights have the benefit of low heat output so you dont need to worry about drying out

the soil or scorching the plants and they use very little electricity For example GlowPanel

LED growing lights cover a 15 square foot area (they are roughly 15 inches on a side) and

consume just 14 watts For growing purposes this light would be suitable for starting

seedlings or for growing herbs or lettuce indoors but is at the lower end of required light output for growing vegetables

Is it green to use LED growing lights Well its definitely an improvement to switch from

any of the other technologies as the amount of electricity youll use for the same amount of

growth is reduced significantly because of the concentration of light in the desired ranges of

the spectrum and because of the improved efficiency of LEDs But in absolute terms I

personally feel that LED growing lights should be used sparingly unless you have a source of carbon-neutral electricity that no one else has a use for

Why Lets consider a 6-square-foot herb garden using the GlowPanel LED growing lights

These lights consume 14 watts each for 15 square feet or 56 watts for the 6-square foot

garden The lights should be on about 12-16 hours a day for growing herbs or lettuce Lets

assume 12 hours to be conservative That meas were using 12 x 56 watts per day or 672 watt-hours Over a three month period that becomes about 60 kilowatt hours

Lets assume that 6-square foot garden produces 12 healthy heads of lettuce over the three

month period Each head of lettuce has therefore cost you 5 kilowatt hours of electricity

and might weigh a pound wet weight - and at about 95 water content would consist of less than an ounce of dried organic matter

Energy consumption is significantly lower for LED lights vs ldquoequivalentrdquo HID lights Most

grow light manufacturers are working to replace the light output of a 400-500 watt HID light

with between 30 and 300 watts of power consumed and some go quite a lot lower The

juryrsquos still out on how these lights truly compare to their HID cousins on garden performance and yield but on the energy promise they seem to perform well

The lights fare well on the heat promise too Most LED grow lights put out very little heat

so do not have any specific cooling requirements A lightrsquos heat output is affected by its

design some lights cluster LEDs in round or square ldquopodsrdquo or ldquorosettesrdquo that are spaced

along horizontal bars These designs help to limit heat accumulation by spacing the LEDs

farther apart Other lights bunch the LEDs close together in a single fixture to provide a

greater light intensity directly below the light These designs can accumulate heat so

generally incorporate heat management features such as heat shielding fans for air cooling

or water cooling

The third promise customized light spectrum is a topic where debates swirl Skeptics do

not believe LEDs can ever produce light that is intense enough to be effective for

photosynthesis no matter what color it is These concerns are based on earlier generation

LEDs that did not put out enough energy to work well as grow lights Todayrsquos ldquothird

generationrdquo LEDs reportedly solve this problem by putting out up to three watts of light

energy per LED a 20-50 fold improvement over second-generation LEDs New-generation

LEDs also have a wider ldquobeam anglerdquo that permits an LED to project light across a 120

degree arc instead of mostly just straight down (ldquopin pointrdquo lighting) This means wider light cones improving light intensity and coverage at the garden canopy

Passionate debates about LED grow light design and effectiveness are waged on a regular

basis in online gardening communities Some posts describe LED grow light trials people are

conducting in their homes While these posts are interesting reading and therersquos a lot to be

learned from them they should also be taken with a grain of salt Many hobbyists want to

debate whether LED grow lights are or can be effective The academic and scientific

communities satisfied for some time that LED grow lights are effective have moved on to

figuring out ldquohowrdquo

Updating Garden Methods for LEDs

One point that LED grow light manufacturers emphasize is that we must update our

gardening methods to use LED grow lights to their best advantage Using an LED grow light

without changing gardening methods will likely result in a disappointing outcome The first

caution is to not overwater Yoursquove eliminated one of the largest sources of heat in your

garden your HID garden lights

With less heat your plants consume less nutrient solution and less of it evaporates thus

less solution is needed One lighting manufacturer also suggests using a weaker nutrient

solution to match lower plant transpiration rates Less solution and less nutrients used this

should be good news right Yes and no Reservoirs can be smaller saving money and

space Fewer expensive bottles of hydroponic nutrient solutions are needed

The dark side is subtle but compelling the most

frequent cause of indoor plant death is

overwatering Itrsquos just as true for plants in a fully

automated indoor garden as it is for an African

violet on the kitchen windowsill Those accustomed

to gardening under HID lights will find that itrsquos

extremely easy to overwater under LED grow

lights Your plants simply need less water when there is less heat

Overwatering can lead to root rot or drowning if itrsquos

not caught and corrected right away When using

LED grow lights be sure to select a porous growing

media to provide adequate drainage and plenty of

air space in the root zone Also let your plants

almost dry more between feedings Overwatering

can also increase garden humidity levels which

can promote the development of fungus and other

garden ills Keep a close watch on growing media

moisture levels and garden relative humidity when

using LED grow lights An LED grow light that emits

some UV-A spectrum (invisible but felt as heat)

may help to kill or retard mildew Maintaining constant air movement within the garden

using oscillating or fixed fans will also help to keep mold and mildew in check

Grow light manufacturers also recommend supplementing the garden atmosphere with

carbon dioxide (CO2) While supplemental CO2 will improve the yield of any garden when

properly applied there are two particular benefits when using CO2 with LED grow lights

First even though an LED grow light may look dim to the human eye it is putting out a lot

of light energy in the spectrum needed for photosynthesis ndash ideally more than the plants

would receive under ldquocomparablerdquo MH or HPS lights Plants need higher CO2 levels in order

to turn this additional light into fuel The second benefit is that with lower heat output there

is less need to vent or air condition the garden space Itrsquos easier to seal the garden environment for CO2 when itrsquos not as hot

Top Two Concerns

We asked several LED lighting manufacturers about the concerns customers express when

considering an LED grow light Two primary concerns emerged

The first is the price for LED grow lights LED grow lights can be purchased on eBay for as

little as $9 for a screw-in replacement grow bulb to as much as $1500 for a water-cooled

garden light fixture reported to be equivalent to a 400- to 500 watt HPS light Donrsquot be

misled by the low price on some of the LED lights on eBay ndash they often include lower-

output inferior LEDs and some of them are recycled traffic signal lights A large number of

these inexpensive LED ldquogrow lightsrdquo may be needed to provide illumination for a standard-

sized hobby garden buyer beware A home gardener should expect to spend between $500

and $1500 for LED grow lights to illuminate a 3rsquo x 3rsquo growing space The ldquototal cost of

ownershiprdquo models discussed earlier are one way to understand the price issue LED grow

lights require a larger up-front investment which should be more than offset by reduced operating costs going forward

The second concern is that nobody

wants to go first More people are

interested in LED grow lights than are

ready to start using them Gardeners

do not want their crop to wind up as

the ldquoguinea pigrdquo in a failed garden

lighting experiment A lot of trials and

research have been conducted in

research laboratories that show LED

grow lights to be effective and cost-

efficient But those trials were done in

a laboratory setting Whatrsquos missing

are verifiable and repeatable

consumer-oriented trials that put LED

grow lights up against their HID

counterparts in conditions that

resemble a hobbyist indoor garden

room Until that happens individual

gardeners can experiment with LED grow lights on their own either on a small scale or by segregating a small number of plants within their garden for trials

Looking Ahead

What is the future of LED grow lights Near-term we should expect to see a wider variety of

LED grow lights coming onto the market These lights will increasingly include higher output

LEDs in a variety of light colors and configurations We expect to see combination lights

hitting the market using LED plus T5 fluorescent or HID garden lights to provide a more balanced spectrum than available from these garden lights used alone

We are starting to see LED grow lights designed to support different plant growth stages

such as grow and bloom and should expect lights to be introduced for specific plants such

as tomatoes herbs or orchids We will see continued improvements in light output

particularly as fourth-generation LEDs continue their migration from the lab to the market

Prices will begin to come down when sales volume increases

In the long run LED lighting could

obsolete almost every other type of

lighting Retrofit LED lamps that fit

into standard fluorescent lighting

fixtures are already available and

LED fixtures are in the works that

will replace street lights stadium

lights and other interior and

exterior lights Already Amsterdam

and Rotterdam in the Netherlands

are testing LED street lighting and

press reports indicate that other

major cities are considering similar trials

LED grow lights will be swept ahead

with the tide of mostly government-

funded research and development

currently underway Research

dollars invested by NASA and other

government agencies around the

globe are fueling tremendous

advances in LED lighting

technologies The energy saving

potential of LED lights is something

these entities cannot ignore if we

can find a way to consume less

energy to light up public and

private spaces we may be able to

postpone or scratch plans to build

new power plants or buy time until we are able to commercialize sustainable methods to generate and transport electricity

There is a lot of promise associated with LED grow lights but there are also unanswered

questions and unresolved debates The products that are available today should produce an

acceptable result so long as the gardener makes appropriate changes to their gardening

methods Wersquore looking forward to further articles and reports that describe how LED grow

lights perform against standard MH and HPS grow lights Wersquore hopeful about how LED grow

lights will fare in such comparisons

LED Growing Lights

Grow more plants with less electricity

Are LED growing lights better than fluorescent metal halide or high pressure sodium grow

lights Will they improve plant growth and will they use less electricity Is growing plants with LED growing lights environmentally friendly

Plants dont use the full visible spectrum to photosynthecize They predominantly use cool

(violet-blue and blue) and warm (orange-red) wavelengths which is a reflection of the

typical colors of natural night on a seasonal basis In the summer months when the sun is

more directly overhead cool colors predominate and tend to encourage healthy vegetative

growth while in spring and fall warm colors take over and tend to encourage flowering and fruiting

A typical metal halide grow light puts out much of its output in wavelength ranges that

plants do not use - cyan green yellow - and very little in the violet or blue regions So with

a metal halide grow light you are typically wasting much of the light shining down on your

plants A daylight metal halide light is more in the blue spectrum and so is useful for the

vegetative stage of growth but not for flowering or fruiting High pressure sodium lights

tend more to the warm red end of the spectrum and so are chiefly useful for flowering and fruiting

You can create your own LED growing lights by combining red and blue LED lights in roughly

a two- to-one proportion (two blue to one red) or buy an LED set designed specifically for

indoor growing which has blue and red LED grow lights in an appropriate proportion LED

grow lights have the benefit of low heat output so you dont need to worry about drying out

the soil or scorching the plants and they use very little electricity For example GlowPanel

LED growing lights cover a 15 square foot area (they are roughly 15 inches on a side) and

consume just 14 watts For growing purposes this light would be suitable for starting

seedlings or for growing herbs or lettuce indoors but is at the lower end of required light output for growing vegetables

Is it green to use LED growing lights Well its definitely an improvement to switch from

any of the other technologies as the amount of electricity youll use for the same amount of

growth is reduced significantly because of the concentration of light in the desired ranges of

the spectrum and because of the improved efficiency of LEDs But in absolute terms I

personally feel that LED growing lights should be used sparingly unless you have a source of carbon-neutral electricity that no one else has a use for

Why Lets consider a 6-square-foot herb garden using the GlowPanel LED growing lights

These lights consume 14 watts each for 15 square feet or 56 watts for the 6-square foot

garden The lights should be on about 12-16 hours a day for growing herbs or lettuce Lets

assume 12 hours to be conservative That meas were using 12 x 56 watts per day or 672 watt-hours Over a three month period that becomes about 60 kilowatt hours

Lets assume that 6-square foot garden produces 12 healthy heads of lettuce over the three

month period Each head of lettuce has therefore cost you 5 kilowatt hours of electricity

and might weigh a pound wet weight - and at about 95 water content would consist of less than an ounce of dried organic matter

Passionate debates about LED grow light design and effectiveness are waged on a regular

basis in online gardening communities Some posts describe LED grow light trials people are

conducting in their homes While these posts are interesting reading and therersquos a lot to be

learned from them they should also be taken with a grain of salt Many hobbyists want to

debate whether LED grow lights are or can be effective The academic and scientific

communities satisfied for some time that LED grow lights are effective have moved on to

figuring out ldquohowrdquo

Updating Garden Methods for LEDs

One point that LED grow light manufacturers emphasize is that we must update our

gardening methods to use LED grow lights to their best advantage Using an LED grow light

without changing gardening methods will likely result in a disappointing outcome The first

caution is to not overwater Yoursquove eliminated one of the largest sources of heat in your

garden your HID garden lights

With less heat your plants consume less nutrient solution and less of it evaporates thus

less solution is needed One lighting manufacturer also suggests using a weaker nutrient

solution to match lower plant transpiration rates Less solution and less nutrients used this

should be good news right Yes and no Reservoirs can be smaller saving money and

space Fewer expensive bottles of hydroponic nutrient solutions are needed

The dark side is subtle but compelling the most

frequent cause of indoor plant death is

overwatering Itrsquos just as true for plants in a fully

automated indoor garden as it is for an African

violet on the kitchen windowsill Those accustomed

to gardening under HID lights will find that itrsquos

extremely easy to overwater under LED grow

lights Your plants simply need less water when there is less heat

Overwatering can lead to root rot or drowning if itrsquos

not caught and corrected right away When using

LED grow lights be sure to select a porous growing

media to provide adequate drainage and plenty of

air space in the root zone Also let your plants

almost dry more between feedings Overwatering

can also increase garden humidity levels which

can promote the development of fungus and other

garden ills Keep a close watch on growing media

moisture levels and garden relative humidity when

using LED grow lights An LED grow light that emits

some UV-A spectrum (invisible but felt as heat)

may help to kill or retard mildew Maintaining constant air movement within the garden

using oscillating or fixed fans will also help to keep mold and mildew in check

Grow light manufacturers also recommend supplementing the garden atmosphere with

carbon dioxide (CO2) While supplemental CO2 will improve the yield of any garden when

properly applied there are two particular benefits when using CO2 with LED grow lights

First even though an LED grow light may look dim to the human eye it is putting out a lot

of light energy in the spectrum needed for photosynthesis ndash ideally more than the plants

would receive under ldquocomparablerdquo MH or HPS lights Plants need higher CO2 levels in order

to turn this additional light into fuel The second benefit is that with lower heat output there

is less need to vent or air condition the garden space Itrsquos easier to seal the garden environment for CO2 when itrsquos not as hot

Top Two Concerns

We asked several LED lighting manufacturers about the concerns customers express when

considering an LED grow light Two primary concerns emerged

The first is the price for LED grow lights LED grow lights can be purchased on eBay for as

little as $9 for a screw-in replacement grow bulb to as much as $1500 for a water-cooled

garden light fixture reported to be equivalent to a 400- to 500 watt HPS light Donrsquot be

misled by the low price on some of the LED lights on eBay ndash they often include lower-

output inferior LEDs and some of them are recycled traffic signal lights A large number of

these inexpensive LED ldquogrow lightsrdquo may be needed to provide illumination for a standard-

sized hobby garden buyer beware A home gardener should expect to spend between $500

and $1500 for LED grow lights to illuminate a 3rsquo x 3rsquo growing space The ldquototal cost of

ownershiprdquo models discussed earlier are one way to understand the price issue LED grow

lights require a larger up-front investment which should be more than offset by reduced operating costs going forward

The second concern is that nobody

wants to go first More people are

interested in LED grow lights than are

ready to start using them Gardeners

do not want their crop to wind up as

the ldquoguinea pigrdquo in a failed garden

lighting experiment A lot of trials and

research have been conducted in

research laboratories that show LED

grow lights to be effective and cost-

efficient But those trials were done in

a laboratory setting Whatrsquos missing

are verifiable and repeatable

consumer-oriented trials that put LED

grow lights up against their HID

counterparts in conditions that

resemble a hobbyist indoor garden

room Until that happens individual

gardeners can experiment with LED grow lights on their own either on a small scale or by segregating a small number of plants within their garden for trials

Looking Ahead

What is the future of LED grow lights Near-term we should expect to see a wider variety of

LED grow lights coming onto the market These lights will increasingly include higher output

LEDs in a variety of light colors and configurations We expect to see combination lights

hitting the market using LED plus T5 fluorescent or HID garden lights to provide a more balanced spectrum than available from these garden lights used alone

We are starting to see LED grow lights designed to support different plant growth stages

such as grow and bloom and should expect lights to be introduced for specific plants such

as tomatoes herbs or orchids We will see continued improvements in light output

particularly as fourth-generation LEDs continue their migration from the lab to the market

Prices will begin to come down when sales volume increases

In the long run LED lighting could

obsolete almost every other type of

lighting Retrofit LED lamps that fit

into standard fluorescent lighting

fixtures are already available and

LED fixtures are in the works that

will replace street lights stadium

lights and other interior and

exterior lights Already Amsterdam

and Rotterdam in the Netherlands

are testing LED street lighting and

press reports indicate that other

major cities are considering similar trials

LED grow lights will be swept ahead

with the tide of mostly government-

funded research and development

currently underway Research

dollars invested by NASA and other

government agencies around the

globe are fueling tremendous

advances in LED lighting

technologies The energy saving

potential of LED lights is something

these entities cannot ignore if we

can find a way to consume less

energy to light up public and

private spaces we may be able to

postpone or scratch plans to build

new power plants or buy time until we are able to commercialize sustainable methods to generate and transport electricity

There is a lot of promise associated with LED grow lights but there are also unanswered

questions and unresolved debates The products that are available today should produce an

acceptable result so long as the gardener makes appropriate changes to their gardening

methods Wersquore looking forward to further articles and reports that describe how LED grow

lights perform against standard MH and HPS grow lights Wersquore hopeful about how LED grow

lights will fare in such comparisons

LED Growing Lights

Grow more plants with less electricity

Are LED growing lights better than fluorescent metal halide or high pressure sodium grow

lights Will they improve plant growth and will they use less electricity Is growing plants with LED growing lights environmentally friendly

Plants dont use the full visible spectrum to photosynthecize They predominantly use cool

(violet-blue and blue) and warm (orange-red) wavelengths which is a reflection of the

typical colors of natural night on a seasonal basis In the summer months when the sun is

more directly overhead cool colors predominate and tend to encourage healthy vegetative

growth while in spring and fall warm colors take over and tend to encourage flowering and fruiting

A typical metal halide grow light puts out much of its output in wavelength ranges that

plants do not use - cyan green yellow - and very little in the violet or blue regions So with

a metal halide grow light you are typically wasting much of the light shining down on your

plants A daylight metal halide light is more in the blue spectrum and so is useful for the

vegetative stage of growth but not for flowering or fruiting High pressure sodium lights

tend more to the warm red end of the spectrum and so are chiefly useful for flowering and fruiting

You can create your own LED growing lights by combining red and blue LED lights in roughly

a two- to-one proportion (two blue to one red) or buy an LED set designed specifically for

indoor growing which has blue and red LED grow lights in an appropriate proportion LED

grow lights have the benefit of low heat output so you dont need to worry about drying out

the soil or scorching the plants and they use very little electricity For example GlowPanel

LED growing lights cover a 15 square foot area (they are roughly 15 inches on a side) and

consume just 14 watts For growing purposes this light would be suitable for starting

seedlings or for growing herbs or lettuce indoors but is at the lower end of required light output for growing vegetables

Is it green to use LED growing lights Well its definitely an improvement to switch from

any of the other technologies as the amount of electricity youll use for the same amount of

growth is reduced significantly because of the concentration of light in the desired ranges of

the spectrum and because of the improved efficiency of LEDs But in absolute terms I

personally feel that LED growing lights should be used sparingly unless you have a source of carbon-neutral electricity that no one else has a use for

Why Lets consider a 6-square-foot herb garden using the GlowPanel LED growing lights

These lights consume 14 watts each for 15 square feet or 56 watts for the 6-square foot

garden The lights should be on about 12-16 hours a day for growing herbs or lettuce Lets

assume 12 hours to be conservative That meas were using 12 x 56 watts per day or 672 watt-hours Over a three month period that becomes about 60 kilowatt hours

Lets assume that 6-square foot garden produces 12 healthy heads of lettuce over the three

month period Each head of lettuce has therefore cost you 5 kilowatt hours of electricity

and might weigh a pound wet weight - and at about 95 water content would consist of less than an ounce of dried organic matter

of light energy in the spectrum needed for photosynthesis ndash ideally more than the plants

would receive under ldquocomparablerdquo MH or HPS lights Plants need higher CO2 levels in order

to turn this additional light into fuel The second benefit is that with lower heat output there

is less need to vent or air condition the garden space Itrsquos easier to seal the garden environment for CO2 when itrsquos not as hot

Top Two Concerns

We asked several LED lighting manufacturers about the concerns customers express when

considering an LED grow light Two primary concerns emerged

The first is the price for LED grow lights LED grow lights can be purchased on eBay for as

little as $9 for a screw-in replacement grow bulb to as much as $1500 for a water-cooled

garden light fixture reported to be equivalent to a 400- to 500 watt HPS light Donrsquot be

misled by the low price on some of the LED lights on eBay ndash they often include lower-

output inferior LEDs and some of them are recycled traffic signal lights A large number of

these inexpensive LED ldquogrow lightsrdquo may be needed to provide illumination for a standard-

sized hobby garden buyer beware A home gardener should expect to spend between $500

and $1500 for LED grow lights to illuminate a 3rsquo x 3rsquo growing space The ldquototal cost of

ownershiprdquo models discussed earlier are one way to understand the price issue LED grow

lights require a larger up-front investment which should be more than offset by reduced operating costs going forward

The second concern is that nobody

wants to go first More people are

interested in LED grow lights than are

ready to start using them Gardeners

do not want their crop to wind up as

the ldquoguinea pigrdquo in a failed garden

lighting experiment A lot of trials and

research have been conducted in

research laboratories that show LED

grow lights to be effective and cost-

efficient But those trials were done in

a laboratory setting Whatrsquos missing

are verifiable and repeatable

consumer-oriented trials that put LED

grow lights up against their HID

counterparts in conditions that

resemble a hobbyist indoor garden

room Until that happens individual

gardeners can experiment with LED grow lights on their own either on a small scale or by segregating a small number of plants within their garden for trials

Looking Ahead

What is the future of LED grow lights Near-term we should expect to see a wider variety of

LED grow lights coming onto the market These lights will increasingly include higher output

LEDs in a variety of light colors and configurations We expect to see combination lights

hitting the market using LED plus T5 fluorescent or HID garden lights to provide a more balanced spectrum than available from these garden lights used alone

We are starting to see LED grow lights designed to support different plant growth stages

such as grow and bloom and should expect lights to be introduced for specific plants such

as tomatoes herbs or orchids We will see continued improvements in light output

particularly as fourth-generation LEDs continue their migration from the lab to the market

Prices will begin to come down when sales volume increases

In the long run LED lighting could

obsolete almost every other type of

lighting Retrofit LED lamps that fit

into standard fluorescent lighting

fixtures are already available and

LED fixtures are in the works that

will replace street lights stadium

lights and other interior and

exterior lights Already Amsterdam

and Rotterdam in the Netherlands

are testing LED street lighting and

press reports indicate that other

major cities are considering similar trials

LED grow lights will be swept ahead

with the tide of mostly government-

funded research and development

currently underway Research

dollars invested by NASA and other

government agencies around the

globe are fueling tremendous

advances in LED lighting

technologies The energy saving

potential of LED lights is something

these entities cannot ignore if we

can find a way to consume less

energy to light up public and

private spaces we may be able to

postpone or scratch plans to build

new power plants or buy time until we are able to commercialize sustainable methods to generate and transport electricity

There is a lot of promise associated with LED grow lights but there are also unanswered

questions and unresolved debates The products that are available today should produce an

acceptable result so long as the gardener makes appropriate changes to their gardening

methods Wersquore looking forward to further articles and reports that describe how LED grow

lights perform against standard MH and HPS grow lights Wersquore hopeful about how LED grow

lights will fare in such comparisons

LED Growing Lights

Grow more plants with less electricity

Are LED growing lights better than fluorescent metal halide or high pressure sodium grow

lights Will they improve plant growth and will they use less electricity Is growing plants with LED growing lights environmentally friendly

Plants dont use the full visible spectrum to photosynthecize They predominantly use cool

(violet-blue and blue) and warm (orange-red) wavelengths which is a reflection of the

typical colors of natural night on a seasonal basis In the summer months when the sun is

more directly overhead cool colors predominate and tend to encourage healthy vegetative

growth while in spring and fall warm colors take over and tend to encourage flowering and fruiting

A typical metal halide grow light puts out much of its output in wavelength ranges that

plants do not use - cyan green yellow - and very little in the violet or blue regions So with

a metal halide grow light you are typically wasting much of the light shining down on your

plants A daylight metal halide light is more in the blue spectrum and so is useful for the

vegetative stage of growth but not for flowering or fruiting High pressure sodium lights

tend more to the warm red end of the spectrum and so are chiefly useful for flowering and fruiting

You can create your own LED growing lights by combining red and blue LED lights in roughly

a two- to-one proportion (two blue to one red) or buy an LED set designed specifically for

indoor growing which has blue and red LED grow lights in an appropriate proportion LED

grow lights have the benefit of low heat output so you dont need to worry about drying out

the soil or scorching the plants and they use very little electricity For example GlowPanel

LED growing lights cover a 15 square foot area (they are roughly 15 inches on a side) and

consume just 14 watts For growing purposes this light would be suitable for starting

seedlings or for growing herbs or lettuce indoors but is at the lower end of required light output for growing vegetables

Is it green to use LED growing lights Well its definitely an improvement to switch from

any of the other technologies as the amount of electricity youll use for the same amount of

growth is reduced significantly because of the concentration of light in the desired ranges of

the spectrum and because of the improved efficiency of LEDs But in absolute terms I

personally feel that LED growing lights should be used sparingly unless you have a source of carbon-neutral electricity that no one else has a use for

Why Lets consider a 6-square-foot herb garden using the GlowPanel LED growing lights

These lights consume 14 watts each for 15 square feet or 56 watts for the 6-square foot

garden The lights should be on about 12-16 hours a day for growing herbs or lettuce Lets

assume 12 hours to be conservative That meas were using 12 x 56 watts per day or 672 watt-hours Over a three month period that becomes about 60 kilowatt hours

Lets assume that 6-square foot garden produces 12 healthy heads of lettuce over the three

month period Each head of lettuce has therefore cost you 5 kilowatt hours of electricity

and might weigh a pound wet weight - and at about 95 water content would consist of less than an ounce of dried organic matter

We are starting to see LED grow lights designed to support different plant growth stages

such as grow and bloom and should expect lights to be introduced for specific plants such

as tomatoes herbs or orchids We will see continued improvements in light output

particularly as fourth-generation LEDs continue their migration from the lab to the market

Prices will begin to come down when sales volume increases

In the long run LED lighting could

obsolete almost every other type of

lighting Retrofit LED lamps that fit

into standard fluorescent lighting

fixtures are already available and

LED fixtures are in the works that

will replace street lights stadium

lights and other interior and

exterior lights Already Amsterdam

and Rotterdam in the Netherlands

are testing LED street lighting and

press reports indicate that other

major cities are considering similar trials

LED grow lights will be swept ahead

with the tide of mostly government-

funded research and development

currently underway Research

dollars invested by NASA and other

government agencies around the

globe are fueling tremendous

advances in LED lighting

technologies The energy saving

potential of LED lights is something

these entities cannot ignore if we

can find a way to consume less

energy to light up public and

private spaces we may be able to

postpone or scratch plans to build

new power plants or buy time until we are able to commercialize sustainable methods to generate and transport electricity

There is a lot of promise associated with LED grow lights but there are also unanswered

questions and unresolved debates The products that are available today should produce an

acceptable result so long as the gardener makes appropriate changes to their gardening

methods Wersquore looking forward to further articles and reports that describe how LED grow

lights perform against standard MH and HPS grow lights Wersquore hopeful about how LED grow

lights will fare in such comparisons

LED Growing Lights

Grow more plants with less electricity

Are LED growing lights better than fluorescent metal halide or high pressure sodium grow

lights Will they improve plant growth and will they use less electricity Is growing plants with LED growing lights environmentally friendly

Plants dont use the full visible spectrum to photosynthecize They predominantly use cool

(violet-blue and blue) and warm (orange-red) wavelengths which is a reflection of the

typical colors of natural night on a seasonal basis In the summer months when the sun is

more directly overhead cool colors predominate and tend to encourage healthy vegetative

growth while in spring and fall warm colors take over and tend to encourage flowering and fruiting

A typical metal halide grow light puts out much of its output in wavelength ranges that

plants do not use - cyan green yellow - and very little in the violet or blue regions So with

a metal halide grow light you are typically wasting much of the light shining down on your

plants A daylight metal halide light is more in the blue spectrum and so is useful for the

vegetative stage of growth but not for flowering or fruiting High pressure sodium lights

tend more to the warm red end of the spectrum and so are chiefly useful for flowering and fruiting

You can create your own LED growing lights by combining red and blue LED lights in roughly

a two- to-one proportion (two blue to one red) or buy an LED set designed specifically for

indoor growing which has blue and red LED grow lights in an appropriate proportion LED

grow lights have the benefit of low heat output so you dont need to worry about drying out

the soil or scorching the plants and they use very little electricity For example GlowPanel

LED growing lights cover a 15 square foot area (they are roughly 15 inches on a side) and

consume just 14 watts For growing purposes this light would be suitable for starting

seedlings or for growing herbs or lettuce indoors but is at the lower end of required light output for growing vegetables

Is it green to use LED growing lights Well its definitely an improvement to switch from

any of the other technologies as the amount of electricity youll use for the same amount of

growth is reduced significantly because of the concentration of light in the desired ranges of

the spectrum and because of the improved efficiency of LEDs But in absolute terms I

personally feel that LED growing lights should be used sparingly unless you have a source of carbon-neutral electricity that no one else has a use for

Why Lets consider a 6-square-foot herb garden using the GlowPanel LED growing lights

These lights consume 14 watts each for 15 square feet or 56 watts for the 6-square foot

garden The lights should be on about 12-16 hours a day for growing herbs or lettuce Lets

assume 12 hours to be conservative That meas were using 12 x 56 watts per day or 672 watt-hours Over a three month period that becomes about 60 kilowatt hours

Lets assume that 6-square foot garden produces 12 healthy heads of lettuce over the three

month period Each head of lettuce has therefore cost you 5 kilowatt hours of electricity

and might weigh a pound wet weight - and at about 95 water content would consist of less than an ounce of dried organic matter

LED Growing Lights

Grow more plants with less electricity

Are LED growing lights better than fluorescent metal halide or high pressure sodium grow

lights Will they improve plant growth and will they use less electricity Is growing plants with LED growing lights environmentally friendly

Plants dont use the full visible spectrum to photosynthecize They predominantly use cool

(violet-blue and blue) and warm (orange-red) wavelengths which is a reflection of the

typical colors of natural night on a seasonal basis In the summer months when the sun is

more directly overhead cool colors predominate and tend to encourage healthy vegetative

growth while in spring and fall warm colors take over and tend to encourage flowering and fruiting

A typical metal halide grow light puts out much of its output in wavelength ranges that

plants do not use - cyan green yellow - and very little in the violet or blue regions So with

a metal halide grow light you are typically wasting much of the light shining down on your

plants A daylight metal halide light is more in the blue spectrum and so is useful for the

vegetative stage of growth but not for flowering or fruiting High pressure sodium lights

tend more to the warm red end of the spectrum and so are chiefly useful for flowering and fruiting

You can create your own LED growing lights by combining red and blue LED lights in roughly

a two- to-one proportion (two blue to one red) or buy an LED set designed specifically for

indoor growing which has blue and red LED grow lights in an appropriate proportion LED

grow lights have the benefit of low heat output so you dont need to worry about drying out

the soil or scorching the plants and they use very little electricity For example GlowPanel

LED growing lights cover a 15 square foot area (they are roughly 15 inches on a side) and

consume just 14 watts For growing purposes this light would be suitable for starting

seedlings or for growing herbs or lettuce indoors but is at the lower end of required light output for growing vegetables

Is it green to use LED growing lights Well its definitely an improvement to switch from

any of the other technologies as the amount of electricity youll use for the same amount of

growth is reduced significantly because of the concentration of light in the desired ranges of

the spectrum and because of the improved efficiency of LEDs But in absolute terms I

personally feel that LED growing lights should be used sparingly unless you have a source of carbon-neutral electricity that no one else has a use for

Why Lets consider a 6-square-foot herb garden using the GlowPanel LED growing lights

These lights consume 14 watts each for 15 square feet or 56 watts for the 6-square foot

garden The lights should be on about 12-16 hours a day for growing herbs or lettuce Lets

assume 12 hours to be conservative That meas were using 12 x 56 watts per day or 672 watt-hours Over a three month period that becomes about 60 kilowatt hours

Lets assume that 6-square foot garden produces 12 healthy heads of lettuce over the three

month period Each head of lettuce has therefore cost you 5 kilowatt hours of electricity

and might weigh a pound wet weight - and at about 95 water content would consist of less than an ounce of dried organic matter

If youve read my Energy saving facts article youll remember that a kilowatt hour of

electricity if produced from coal requires about 1 lb of coal to be burned and produces just

under 3 lb of CO2 (the main greenhouse gas behind climate change) Remember that coal is

nothing more than fossilized plants So in essence you are consuming 5 lb of coal

(fossilized dried organic matter) to produce what amounts to one ounce of dry organic matter Thats an energy efficiency ratio of 160th or 17

If you happen to have a wind turbine on your property and the electricity isnt otherwise

used (and you dont have a grid intertie) theres no harm in using that electricity to grow

your own food or start your own seedlings But if youre grid connected or buy your power

off the grid its probably much better not to use any form of grow light from an environmental perspective

Of course thats not the only criteria If youre determined to grow heritage plants for

instance and you dont have a local greenhouse that grows them (using natural light) you

may want to start seedlings yourself using LED growing lights to supplement a daylight

source for a few hours a day And if you live so far from the nearest available lettuce that

youd have to make an extra trip in your car to buy a head of lettuce it might make sense

to burn the equivalent of five pounds worth of coal energy in your LED growing lights to

avoid the drive But since this website is dedicated to helping people make energy efficient

choices its important to point out here that the best way of being energy efficient is to

reduce your use of energy

LＥＤの植物工場への応用

渡辺博之

Light Emitting Diodes as the Irradiation Source for Plant Factories Hiroyuki WATANABE

Yokohama Research Center Mitsubishi Chemical Corporation 1000 Kamoshida-cho Aoba-ku Yokohama

Kanagawa 227

Light emitting diodes (LEDs) are a potential irradiation source for intensive plant culture systems like plant factories

LEDs have small size low mass a long functional life and narrow spectral output We have examined the growth

profiles of leaf lettuce and other plant species grown under red light with supplemental blue and far-red light of

LEDs compared with other artificial light On the basis of our experimental data the characteristics of LEDs as

irradiation source for plants and the prospects for plant factory equipping LED lighting systems are overviewed in

this paper

Key Words Light emitting diode Laser diode Plant factory Plant growth

1はじめに

ＬＥＤは単色光をshyし赤外線の放射を極めて低shy抑えられるうえコンパクトで耐久性が

高いなど植物栽培用の光源として他のランプにはない優れた性質を持つ 12)ＬＤと比較すると放射

スペクトルの幅が大きいがもともと植物の光受容体自身がそれほど幅の狭い吸収スペクトルを持って

おらず植物の生育にとって放射スペクトルの違いがＬＥＤに不利にshyshy可能性は低い植物工

場の光源としてＬＥＤとＬＤのどちらを選ぶかを考えるとき判断材料としてはそれらの電気から光

への変換効率（外部量子効率）および光出力nbspたりのランプコストの２点が重要だと考えている

植物工場野菜の生産コストにしめる施設償却費の割合は予想以上に大きshy太陽光併用型で 20～

25人工光完全制御型では 30～35に達すると試算されるどちらの型式の場合でもそれらは消費電

力コストを大きshy上回っている従って植物工場を普及するためには消費電力の削減以上に施設

建設費をどのように減らすかが大きな課題でnbspり設置できるランプもコスト面から大きshy制

約を受ける

現在植物栽培に利用できる波長域のＬＤの外部量子効率はＬＥＤを上回っているが出力nbspた

りのランプコストもＬＥＤより高い筆者らの試算ではサラダナ１株nbspたりの生産コストで比較

してＬＤでのランプ償却費の上昇は現状ではＬＤによる消費電力の削減を完全に相殺してしまう

従って将来的にはともかshy現状ではＬＤよりもＬＥＤの方が野菜生産のトータルコストでは有利

でnbspろうと考えている

こうした背景から筆者らは数年前よりＬＥＤ光源による植物栽培試験を行ってきたＬＥＤ光によ

る植物栽培の試験結果は次のステップとしてＬＤ植物工場を検討する場合にも基礎データとして参考

になると考えているここではわれわれのＬＥＤレタス栽培試験結果を中心に植物栽培光源としての

ＬＥＤの特徴ＬＥＤ植物工場の可能性と課題について紹介する

2植物栽培光源としてのＬＥＤの特徴

ＬＤでの植物栽培の解説と一部重なるがここでまず植物栽培光源としてのＬＥＤの特徴について説

明する

２１ 照射波長の制御

前述のようにＬＤほどではないもののＬＥＤで出力されるスペクトルの半値幅は比較的小さshy

他の放電管型光源に見られるような輝線スペクトルの混入もないたとえば植物栽培で中心的に使用

する赤色ＬＥＤのスペクトル半値幅は 20 - 30nmでnbspりぼぼ純色に近い現在では可視赤外領域

から目的に合った単色光を自由に組み合わせて利用することが可能でnbspる

植物は可視光の中で特定の波長の光を利用しており①光合成反応に用いられる赤色光②shy光

反応系に用いられる青色光③フゖトクローム系を可逆的にスッチングする赤色光と遠赤色光の３種

類の光反応系が存在すると考えられている（Table１）ＬＥＤを用いることによって必要な波長の光を

集中的にかつバランス良shy照射することが可能でnbspるこのことは結果的に栽培の効率化に

寄与しまた開花や結実時期の調節収穫物の草型や栄養成分のコントロールなどに利用できると考え

られる

Table1 Photoreceptor and physiological response in plant

Photoreceptor Peak wavelength of action

spectrum Physiological response

Photosynthesis electron

transport system 660-680nm(red) CO2assimilation

High energy reaction system 450-470nm(blue) Photomorphogenesis(Phototropismstem shortening

etc)

Photochrome system Pr660-670(red) Photomorphogenesis (Germinationflower

differentiation etc)

Pfr730-740nm(far-red) Back-reaction of Pr response

２２ 近接照明

植物栽培に利用する可視領域のＬＥＤ光には赤外領域のエネルギー放射をほとんど含まないことか

ら光源を栽培植物の極めて近shyに設置することができる実際ＬＥＤランプでパネル光源を製作

しそれに葉が接触するような状態でレタスなどの栽培を続けても熱線による葉焼けなどの障害が認

められないこのようにＬＥＤ光源を栽培植物の大きさが許すギリギリの位置に設置して近接照明する

ことにより植物の光利用効率を高めさらにそうした小さな栽培ユニットを何層も積み重ねることによ

り全体として非常にコンパクトな栽培装置に仕上げることが可能でnbspる

植物栽培に必要な光量をＬＥＤで確保するためにはチップを高密度で配置し比較的大きな電力で駆

動させる必要がnbspるそのような場合にはチップのshy熱によるランプやランプ基盤の温度上

昇は避けられない特に栽培ユニットを積層したような集約的な栽培装置を想定した場合栽培シス

テム内の蓄熱温度上昇を避けるためにはランプ基盤やランプユニットの局所的な除熱冷却装置を

備える必要がnbspる逆にＬＥＤは赤外領域のエネルギー放射が極めてshyないことから光源

部分の除熱を行うことによって栽培システム全体の温度上昇を防ぐことができると考えられるこのこ

とは閉鎖型の植物工場で常に問題となる栽培系内の温度管理にかかわるランニングコストを現状の空

調方式と比べ大幅に低減することにつながると考えられる

２3 パルス光照射

ＬＥＤはＬＤ同様極めて短周期のパルス光照射に適している通常フゖラメントを持つ植物栽培

光源でのパルス光照射はランプに対する負担が大きshyランプ寿命を極端に短shyしてしまう光

出力に関してもパルス化すると連続点灯に比べて低下する場合が多いＬＥＤは高速応答性が極めて

高shy電源との間に簡単なパルスshy生器を設置するだけでナノ秒以下の短周期でのパルス光化が

可能でnbspる

植物の生長特に光合成反応に対しては連続光よりもパルス光の方が光の利用効率が高いと考えら

れている 34）今後植物栽培におけるパルス光照射のメリットの大きさを定量的に確認する必要が

nbspるがパルスshy生器などの装置的なコストを上回る栽培効率向上が認められればＬＥＤはＬ

Ｄとともに非常に優れたパルス栽培光源ということができる

２４ 耐久性コンパクト

通常の使用条件で赤色ＬＥＤのランプ寿命は５万時間以上nbspりこれは１日 12 時間照明の植物工

場を 10 年以上稼shyさせる耐久性でnbspるさらにＬＥＤは形状が非常にコンパクトでnbspる

ことから光源部分の形状をかなり自由に設計できる例えば厚さ数ミリのパネル光源はもちろんの

ことさらに薄いシート状の光源や紐状の線光源なども可能でnbspるこうしたＬＥＤの耐久性やラン

プ形状の特徴は植物工場の光源ユニットを設計するうえで大きな自由度を提供する

3リーフレタス栽培試験

31 赤色青色ＬＥＤによる栽培試験

植物の光反応系の活性スペクトルに合わせ３種類のピーク波長（青色 450nm赤色 660 nm遠赤色

730nmshy光スペクトルは Fig 1 参照）を持つＬＥＤを選択しリーフレタスの水耕栽培を行った

ＬＥＤパネル（新光電子製）は45 x 45cm のゕルミフレームに 1000 個（25 列40 段）の砲弾型ＬＥＤ

を設置したもので列毎にピーク波長の変換光出力の調節ができるよう設計した（Fig 2）湛液式水

耕装置（新和製）を用い気温湿度ＣＯ2濃度をコントロールしたンキュベーター内でリーフレ

タス（品種レッドフゔヤー）を水耕栽培し生育に必要な光量と波長構成を調べた（Fig 3）56）

その結果リーフレタスは光合成有効光量子束密度（ＰＰＦＤ）で全光量として 100μmolｍ-2ｓ-

1青色光を８以上添加した赤色光を照射することにより自然光と同様の草型葉色を保ちつつ効

率良shy栽培できることが判明した（Fig 4）栽培中に青色光が不足すると節間と葉柄の伸長が促進

されいわゆる徒長症状を呈するしかしこの症状は赤色光量の増加によってnbspる程度回避でき

ることも見いだされた遠赤色光はこの条件でのリーフレタス栽培には必要なshy逆に草型を乱し

て生育を妨げることが示された

32 パルス光による栽培試験

前段で用いたＬＥＤパネル光源にパルスshy生器を備えた電源装置（新光電子製）を接続し照射

光を周期 10μｓ～10ｍｓデューテゖー比（ＤＴ比明期時間周期）10～50の間で変化させリーフ

レタス苗を栽培した 7）

まずパルス光の消費電力を 100Ｗｍ-2ＤＴ比を 50に固定し周期を 10μｓから 10ｍｓに変化させ

てリーフレタス苗を 20 日間栽培したその結果周期を 100μｓ以下のパルス光にした場合連続光に比

べ約 20の生育促進効果が認められ（Fig 5 左図）短周期のパルス光がリーフレタスの生育に好影響

を与えることが判明した次にパルス光の周期を 10μｓに固定しＤＴ比を 10から 50まで変化さ

せた明期の消費電力を調節し暗期を含めた平均消費電力を 100Ｗｍ-2 になるように設定した結果

はＤＴ比 25から 50で生育が促進されるのに対しＤＴ比 10ではパルス化の効果はほとんど失わ

れることが明らかとなった（Fig5)

３３ 水冷式ＬＥＤパネル光源を用いた栽培試験

ＬＥＤの外部量子効率は現在高効率とされる赤色光ＬＥＤでも 22程度でnbspる残りの電気エ

ネルギーの大部分はチップ自身のshy熱として消耗すると考えられるそこで Fig 6 に示す構造の水冷

式ＬＥＤパネル光源（ピーク波長 660nm）を試作したこのパネルではＬＥＤ集積基盤のnbsp側を

冷却水で除熱することによりパネル温度を一定に保ちshy光面側への熱の移動をほとんど遮断するこ

とができるその上ＬＥＤチップのｐ-ｎ接合部の温度上昇を防ぎ定格電流の約５倍の順方向電流で

駆動してもshy光効率の低下や際立った寿命の短縮は認められなかった

このＬＥＤパネルを Fig 7 に示す閉鎖型栽培装置に組み込みリーフレタスの栽培を試みたこの栽

培装置ではＬＥＤパネルからの熱の放出がないことからＬＥＤパネルの周囲を完全に密閉することが

できる栽培室のまわりを白色ゕクリル板で密閉した結果放射された光は栽培室からほとんど漏れる

ことがなshyその結果栽培ボード上のＰＰＦＤは飛躍的に増加した（Fig 8）またＬＥＤパネルの

水冷により栽培室の温度上昇は完全に防ぐことができた冷却媒体に水を使うことにより通常のエ

ゕコン空調と比べてシステムの温度制御にかかる電力を約半分に低減することができたまた栽培した

リーフレタスの生育状態も良好だった 8）

4特定の植物生理に対する影響

光合成反応を介して光は植物のエネルギー源になると同時にshy芽展葉草丈伸長花芽形成な

ど植物組織や器官の分化形態形成にも深shy関わっているレタス以外の色々な植物にＬＥＤ青色光

赤色光遠赤色光を照射し植物の器官分化形態形成にどのような影響を与えるかを調べたところ

種々の興味深い現象が認められた 5）

たとえばコマツナとチンゲンサは同じゕブラナ科に属し分類学上ではかなり近縁の植物で

nbspるところが遠赤色光に対する反応は両者で異なりコマツナは遠赤色光に対して顕著な葉柄伸

長を示すが節間には全shy影響しなかった（Fig 9 上図）一方チンゲンサでは遠赤色光は節間

伸長のみに影響し葉柄伸長には影響しなかった（Fig 9 下図）またハツカダコンは赤色光のみで

地上部は正常な草型に生育するが根部の肥大には青色光の添加が不可欠でnbspった（Fig 10）

日長の変化による花芽形成にはフゖトクローム系の赤色光と遠赤色光が関わっているたとえばキ

クなど短日植物（昼時間の減shyによって開花を誘導する植物群）の長日処理（夜間照明によって昼時

間を延長させる処理）による花芽形成抑制に対しては赤色光が有効でnbspることが知られている

白色輪ギクを用いてＬＥＤ赤色光による花芽抑制効果を調査したところ通常の白熱電灯栽培に比較し

て消費電力を 70以上削減できることが明らかとなったその上収穫されたキクは品質的にも優れて

おりＬＥＤによるキク電照栽培のメリットを確認することができた 910）

5ＬＥＤ植物工場の可能性

植物栽培用光源としてのＬＥＤの最大の利点はコンパクトな装置で栽培植物の生長や特定の植物生

理を精密に制御できる点にnbspる例えば植物の植えつけボードからＬＥＤパネルまでの高さは栽

培する植物の最大草丈分程度を確保すればよshyレタスサラダナでnbspれば約 20cm通常のプ

ラグ苗では 10cm もとれば十分でnbspるそうした栽培ユニットを何層にも積み重ねることによりス

ペースを立体的に活用しコンパクトな栽培装置に床面積の数倍の栽培面積を確保することは容易で

nbspるまた栽培装置の小型化は温度管理のコストメリットも大きい

さらに栽培植物の生育ステージに合わせて照射波長や光量をプログラム制御することも容易で

nbspるその結果栽培期間の短縮や増収効果健苗育成効果などが期待できる高辻らはＬＥＤによ

るサラダナ栽培において明暗周期を短shyすることによって特に大きな増収効果が得られることを

報告している 11）また波長光量の制御により花芽形成や草型のコントロール 9）可食部やその中の

栄養成分の増量など 12）目的とする植物生理現象を必要なタミングで誘導することも可能でnbspる

このような植物栽培光源としてのＬＥＤのメリットを最大に利用するには太陽光を併用せず人工光

のみの完全制御型植物工場の方がＬＥＤには適していると考えている

電力コストの削減や栽培植物の生長生理の正確なコントロールへの期待が大きいＬＥＤ光源で

nbspるがまずその植物栽培光源としての性能やメリットをこれまで以上に定量的に把握することが必

要でnbspろう普及性のnbspる植物工場の開shyでの最大の課題はいかに野菜のトータルの生

産コストを下げるかに尽きると考えている生産コストの内建設費などのニシャルコストの削減と

電力費などランニングコストの削減は相反する場合が多いいかに低コストの資材を使って電力を使

わない栽培システムを作るか両者のかね合いで装置の備えるべき機能性能を取捨選択し栽培装置

全体としてコストと性能のバランスのとれた栽培システムを構築していshyことが必要でnbspる

6おわりに

人工光による植物栽培はこれまで照明用のランプを適用して行われてきたそれら照明用ランプが照

射する光は基本的には人の目に明るい波長特性を持ったものでnbspり植物の利用特性に沿ったも

のではない正確に植物の好みに合ったいうなれば植物にオシ光環境はＬＥＤやＬＤを光源と

することによって初めて実現されるといえる植物の光利用特性をふまえ植物生長および種々の植物

生理現象を正確に制御できる機能を持った栽培装置をＬＥＤさらにはＬＤを光源として用いること

によってシステム化したいと考えている

１）高辻正基植物工場の基礎と実際（裳華房 1996）p85 ２）渡辺博之ＬＥＤ光源の植物栽培利用（植物工場実用化ビジネス研究部会資料 1995） ３）岩波洋造光合成の世界（講談社ブルーバックス）p152 ４）高辻正基野菜工場（丸善 1986）p127 ５）渡辺博之田中史宏遠藤shy弘ら 園芸学会誌 64(別 1)(1995)390 ６）渡辺博之田中史宏ら日本植物工場学会平成 7 年度大会要旨（1995）p17 ７）渡辺博之田中史宏遠藤shy弘日本植物工場学会平成 7 年度大会要旨（1995）p19 ８）渡辺博之田中史宏吉野徹日本植物工場学会平成 8 年度大会要旨（1996）p23 ９）渡辺博之河合成典ら 園芸学会誌 65(別 1)（1996）452 １０）渡辺博之河合成典ら 園芸学会誌 65(別 2)（1996）568 １１）高辻正基釜谷慎太郎榎本岳夫植物工場学会誌 8(2) （1996）119 １２）田中史宏渡辺博之遠藤shy弘ら園芸学会誌 64(別 1) （1995）392

環境ンフォメーション

ＬＥＤによるレタス栽培

太陽からの光が遮断される室内で効率よく植物を育てられるか

近年屋内で温度や湿度光（照明）等の環境条件を人工的に制御する事により農薬を使用せずに農作物を生産す

る技術が注目を浴びています

その太陽光の変わりに使用する光源として注目を浴びているのがＬＥＤ（発光ダオード）です従来光源として

考えられていた蛍光灯に比してＬＥＤを使用する事により消費電力を大幅に削減できる事が理由の一端に挙げられ

ます

県立中央農業高校（海老名市中新田）三年の岡崎仁美さん（18）がそのＬＥＤを使用しレタスを栽培する研究に

取り組みその研究成果が第五十二回日本学生科学賞県作品展で県知事賞に輝いています

その研究内容とは『蛍光灯より寿命が長く消費電力の少ないＬＥＤを使用する事により省エネかつ高品質な食

物を育てられるのでは』と着想しその有効性を実験しました

その内容は『赤』『青』『赤白混合』『紫外線』『赤外線』等様々な波長の 9 種類のＬＥＤの光を 1 日 16 時間

当てて2 週間レタスを栽培

その結果として『赤白混合』の光を当てたレタスが最も高品質に育ったそうですその上蛍光灯を使用しての栽培

に比して消費電力は約１２と高い省エネ効果も得られました

進むＬＥＤの有効利用は省エネ等の地球温暖化対策だけではなく農業の分野にも大きな力となっているのですね

２１ 照射波長の制御

前述のようにＬＤほどではないもののＬＥＤで出力されるスペクトルの半値幅は比較的小さshy

他の放電管型光源に見られるような輝線スペクトルの混入もないたとえば植物栽培で中心的に使用

する赤色ＬＥＤのスペクトル半値幅は 20 - 30nmでnbspりぼぼ純色に近い現在では可視赤外領域

から目的に合った単色光を自由に組み合わせて利用することが可能でnbspる

植物は可視光の中で特定の波長の光を利用しており①光合成反応に用いられる赤色光②shy光

反応系に用いられる青色光③フゖトクローム系を可逆的にスッチングする赤色光と遠赤色光の３種

類の光反応系が存在すると考えられている（Table１）ＬＥＤを用いることによって必要な波長の光を

集中的にかつバランス良shy照射することが可能でnbspるこのことは結果的に栽培の効率化に

寄与しまた開花や結実時期の調節収穫物の草型や栄養成分のコントロールなどに利用できると考え

られる

Table1 Photoreceptor and physiological response in plant

Photoreceptor Peak wavelength of action

spectrum Physiological response

Photosynthesis electron

transport system 660-680nm(red) CO2assimilation

High energy reaction system 450-470nm(blue) Photomorphogenesis(Phototropismstem shortening

etc)

Photochrome system Pr660-670(red) Photomorphogenesis (Germinationflower

differentiation etc)

Pfr730-740nm(far-red) Back-reaction of Pr response

２２ 近接照明

植物栽培に利用する可視領域のＬＥＤ光には赤外領域のエネルギー放射をほとんど含まないことか

ら光源を栽培植物の極めて近shyに設置することができる実際ＬＥＤランプでパネル光源を製作

しそれに葉が接触するような状態でレタスなどの栽培を続けても熱線による葉焼けなどの障害が認

められないこのようにＬＥＤ光源を栽培植物の大きさが許すギリギリの位置に設置して近接照明する

ことにより植物の光利用効率を高めさらにそうした小さな栽培ユニットを何層も積み重ねることによ

り全体として非常にコンパクトな栽培装置に仕上げることが可能でnbspる

植物栽培に必要な光量をＬＥＤで確保するためにはチップを高密度で配置し比較的大きな電力で駆

動させる必要がnbspるそのような場合にはチップのshy熱によるランプやランプ基盤の温度上

昇は避けられない特に栽培ユニットを積層したような集約的な栽培装置を想定した場合栽培シス

テム内の蓄熱温度上昇を避けるためにはランプ基盤やランプユニットの局所的な除熱冷却装置を

備える必要がnbspる逆にＬＥＤは赤外領域のエネルギー放射が極めてshyないことから光源

部分の除熱を行うことによって栽培システム全体の温度上昇を防ぐことができると考えられるこのこ

とは閉鎖型の植物工場で常に問題となる栽培系内の温度管理にかかわるランニングコストを現状の空

調方式と比べ大幅に低減することにつながると考えられる

２3 パルス光照射

ＬＥＤはＬＤ同様極めて短周期のパルス光照射に適している通常フゖラメントを持つ植物栽培

光源でのパルス光照射はランプに対する負担が大きshyランプ寿命を極端に短shyしてしまう光

出力に関してもパルス化すると連続点灯に比べて低下する場合が多いＬＥＤは高速応答性が極めて

高shy電源との間に簡単なパルスshy生器を設置するだけでナノ秒以下の短周期でのパルス光化が

可能でnbspる

植物の生長特に光合成反応に対しては連続光よりもパルス光の方が光の利用効率が高いと考えら

れている 34）今後植物栽培におけるパルス光照射のメリットの大きさを定量的に確認する必要が

nbspるがパルスshy生器などの装置的なコストを上回る栽培効率向上が認められればＬＥＤはＬ

Ｄとともに非常に優れたパルス栽培光源ということができる

２４ 耐久性コンパクト

通常の使用条件で赤色ＬＥＤのランプ寿命は５万時間以上nbspりこれは１日 12 時間照明の植物工

場を 10 年以上稼shyさせる耐久性でnbspるさらにＬＥＤは形状が非常にコンパクトでnbspる

ことから光源部分の形状をかなり自由に設計できる例えば厚さ数ミリのパネル光源はもちろんの

ことさらに薄いシート状の光源や紐状の線光源なども可能でnbspるこうしたＬＥＤの耐久性やラン

プ形状の特徴は植物工場の光源ユニットを設計するうえで大きな自由度を提供する

3リーフレタス栽培試験

31 赤色青色ＬＥＤによる栽培試験

植物の光反応系の活性スペクトルに合わせ３種類のピーク波長（青色 450nm赤色 660 nm遠赤色

730nmshy光スペクトルは Fig 1 参照）を持つＬＥＤを選択しリーフレタスの水耕栽培を行った

ＬＥＤパネル（新光電子製）は45 x 45cm のゕルミフレームに 1000 個（25 列40 段）の砲弾型ＬＥＤ

を設置したもので列毎にピーク波長の変換光出力の調節ができるよう設計した（Fig 2）湛液式水

耕装置（新和製）を用い気温湿度ＣＯ2濃度をコントロールしたンキュベーター内でリーフレ

タス（品種レッドフゔヤー）を水耕栽培し生育に必要な光量と波長構成を調べた（Fig 3）56）

その結果リーフレタスは光合成有効光量子束密度（ＰＰＦＤ）で全光量として 100μmolｍ-2ｓ-

1青色光を８以上添加した赤色光を照射することにより自然光と同様の草型葉色を保ちつつ効

率良shy栽培できることが判明した（Fig 4）栽培中に青色光が不足すると節間と葉柄の伸長が促進

されいわゆる徒長症状を呈するしかしこの症状は赤色光量の増加によってnbspる程度回避でき

ることも見いだされた遠赤色光はこの条件でのリーフレタス栽培には必要なshy逆に草型を乱し

て生育を妨げることが示された

32 パルス光による栽培試験

前段で用いたＬＥＤパネル光源にパルスshy生器を備えた電源装置（新光電子製）を接続し照射

光を周期 10μｓ～10ｍｓデューテゖー比（ＤＴ比明期時間周期）10～50の間で変化させリーフ

レタス苗を栽培した 7）

まずパルス光の消費電力を 100Ｗｍ-2ＤＴ比を 50に固定し周期を 10μｓから 10ｍｓに変化させ

てリーフレタス苗を 20 日間栽培したその結果周期を 100μｓ以下のパルス光にした場合連続光に比

べ約 20の生育促進効果が認められ（Fig 5 左図）短周期のパルス光がリーフレタスの生育に好影響

を与えることが判明した次にパルス光の周期を 10μｓに固定しＤＴ比を 10から 50まで変化さ

せた明期の消費電力を調節し暗期を含めた平均消費電力を 100Ｗｍ-2 になるように設定した結果

はＤＴ比 25から 50で生育が促進されるのに対しＤＴ比 10ではパルス化の効果はほとんど失わ

れることが明らかとなった（Fig5)

３３ 水冷式ＬＥＤパネル光源を用いた栽培試験

ＬＥＤの外部量子効率は現在高効率とされる赤色光ＬＥＤでも 22程度でnbspる残りの電気エ

ネルギーの大部分はチップ自身のshy熱として消耗すると考えられるそこで Fig 6 に示す構造の水冷

式ＬＥＤパネル光源（ピーク波長 660nm）を試作したこのパネルではＬＥＤ集積基盤のnbsp側を

冷却水で除熱することによりパネル温度を一定に保ちshy光面側への熱の移動をほとんど遮断するこ

とができるその上ＬＥＤチップのｐ-ｎ接合部の温度上昇を防ぎ定格電流の約５倍の順方向電流で

駆動してもshy光効率の低下や際立った寿命の短縮は認められなかった

このＬＥＤパネルを Fig 7 に示す閉鎖型栽培装置に組み込みリーフレタスの栽培を試みたこの栽

培装置ではＬＥＤパネルからの熱の放出がないことからＬＥＤパネルの周囲を完全に密閉することが

できる栽培室のまわりを白色ゕクリル板で密閉した結果放射された光は栽培室からほとんど漏れる

ことがなshyその結果栽培ボード上のＰＰＦＤは飛躍的に増加した（Fig 8）またＬＥＤパネルの

水冷により栽培室の温度上昇は完全に防ぐことができた冷却媒体に水を使うことにより通常のエ

ゕコン空調と比べてシステムの温度制御にかかる電力を約半分に低減することができたまた栽培した

リーフレタスの生育状態も良好だった 8）

4特定の植物生理に対する影響

光合成反応を介して光は植物のエネルギー源になると同時にshy芽展葉草丈伸長花芽形成な

ど植物組織や器官の分化形態形成にも深shy関わっているレタス以外の色々な植物にＬＥＤ青色光

赤色光遠赤色光を照射し植物の器官分化形態形成にどのような影響を与えるかを調べたところ

種々の興味深い現象が認められた 5）

たとえばコマツナとチンゲンサは同じゕブラナ科に属し分類学上ではかなり近縁の植物で

nbspるところが遠赤色光に対する反応は両者で異なりコマツナは遠赤色光に対して顕著な葉柄伸

長を示すが節間には全shy影響しなかった（Fig 9 上図）一方チンゲンサでは遠赤色光は節間

伸長のみに影響し葉柄伸長には影響しなかった（Fig 9 下図）またハツカダコンは赤色光のみで

地上部は正常な草型に生育するが根部の肥大には青色光の添加が不可欠でnbspった（Fig 10）

日長の変化による花芽形成にはフゖトクローム系の赤色光と遠赤色光が関わっているたとえばキ

クなど短日植物（昼時間の減shyによって開花を誘導する植物群）の長日処理（夜間照明によって昼時

間を延長させる処理）による花芽形成抑制に対しては赤色光が有効でnbspることが知られている

白色輪ギクを用いてＬＥＤ赤色光による花芽抑制効果を調査したところ通常の白熱電灯栽培に比較し

て消費電力を 70以上削減できることが明らかとなったその上収穫されたキクは品質的にも優れて

おりＬＥＤによるキク電照栽培のメリットを確認することができた 910）

5ＬＥＤ植物工場の可能性

植物栽培用光源としてのＬＥＤの最大の利点はコンパクトな装置で栽培植物の生長や特定の植物生

理を精密に制御できる点にnbspる例えば植物の植えつけボードからＬＥＤパネルまでの高さは栽

培する植物の最大草丈分程度を確保すればよshyレタスサラダナでnbspれば約 20cm通常のプ

ラグ苗では 10cm もとれば十分でnbspるそうした栽培ユニットを何層にも積み重ねることによりス

ペースを立体的に活用しコンパクトな栽培装置に床面積の数倍の栽培面積を確保することは容易で

nbspるまた栽培装置の小型化は温度管理のコストメリットも大きい

さらに栽培植物の生育ステージに合わせて照射波長や光量をプログラム制御することも容易で

nbspるその結果栽培期間の短縮や増収効果健苗育成効果などが期待できる高辻らはＬＥＤによ

るサラダナ栽培において明暗周期を短shyすることによって特に大きな増収効果が得られることを

報告している 11）また波長光量の制御により花芽形成や草型のコントロール 9）可食部やその中の

栄養成分の増量など 12）目的とする植物生理現象を必要なタミングで誘導することも可能でnbspる

このような植物栽培光源としてのＬＥＤのメリットを最大に利用するには太陽光を併用せず人工光

のみの完全制御型植物工場の方がＬＥＤには適していると考えている

電力コストの削減や栽培植物の生長生理の正確なコントロールへの期待が大きいＬＥＤ光源で

nbspるがまずその植物栽培光源としての性能やメリットをこれまで以上に定量的に把握することが必

要でnbspろう普及性のnbspる植物工場の開shyでの最大の課題はいかに野菜のトータルの生

産コストを下げるかに尽きると考えている生産コストの内建設費などのニシャルコストの削減と

電力費などランニングコストの削減は相反する場合が多いいかに低コストの資材を使って電力を使

わない栽培システムを作るか両者のかね合いで装置の備えるべき機能性能を取捨選択し栽培装置

全体としてコストと性能のバランスのとれた栽培システムを構築していshyことが必要でnbspる

6おわりに

人工光による植物栽培はこれまで照明用のランプを適用して行われてきたそれら照明用ランプが照

射する光は基本的には人の目に明るい波長特性を持ったものでnbspり植物の利用特性に沿ったも

のではない正確に植物の好みに合ったいうなれば植物にオシ光環境はＬＥＤやＬＤを光源と

することによって初めて実現されるといえる植物の光利用特性をふまえ植物生長および種々の植物

生理現象を正確に制御できる機能を持った栽培装置をＬＥＤさらにはＬＤを光源として用いること

によってシステム化したいと考えている

１）高辻正基植物工場の基礎と実際（裳華房 1996）p85 ２）渡辺博之ＬＥＤ光源の植物栽培利用（植物工場実用化ビジネス研究部会資料 1995） ３）岩波洋造光合成の世界（講談社ブルーバックス）p152 ４）高辻正基野菜工場（丸善 1986）p127 ５）渡辺博之田中史宏遠藤shy弘ら 園芸学会誌 64(別 1)(1995)390 ６）渡辺博之田中史宏ら日本植物工場学会平成 7 年度大会要旨（1995）p17 ７）渡辺博之田中史宏遠藤shy弘日本植物工場学会平成 7 年度大会要旨（1995）p19 ８）渡辺博之田中史宏吉野徹日本植物工場学会平成 8 年度大会要旨（1996）p23 ９）渡辺博之河合成典ら 園芸学会誌 65(別 1)（1996）452 １０）渡辺博之河合成典ら 園芸学会誌 65(別 2)（1996）568 １１）高辻正基釜谷慎太郎榎本岳夫植物工場学会誌 8(2) （1996）119 １２）田中史宏渡辺博之遠藤shy弘ら園芸学会誌 64(別 1) （1995）392

環境ンフォメーション

ＬＥＤによるレタス栽培

太陽からの光が遮断される室内で効率よく植物を育てられるか

近年屋内で温度や湿度光（照明）等の環境条件を人工的に制御する事により農薬を使用せずに農作物を生産す

る技術が注目を浴びています

その太陽光の変わりに使用する光源として注目を浴びているのがＬＥＤ（発光ダオード）です従来光源として

考えられていた蛍光灯に比してＬＥＤを使用する事により消費電力を大幅に削減できる事が理由の一端に挙げられ

ます

県立中央農業高校（海老名市中新田）三年の岡崎仁美さん（18）がそのＬＥＤを使用しレタスを栽培する研究に

取り組みその研究成果が第五十二回日本学生科学賞県作品展で県知事賞に輝いています

その研究内容とは『蛍光灯より寿命が長く消費電力の少ないＬＥＤを使用する事により省エネかつ高品質な食

物を育てられるのでは』と着想しその有効性を実験しました

その内容は『赤』『青』『赤白混合』『紫外線』『赤外線』等様々な波長の 9 種類のＬＥＤの光を 1 日 16 時間

当てて2 週間レタスを栽培

その結果として『赤白混合』の光を当てたレタスが最も高品質に育ったそうですその上蛍光灯を使用しての栽培

に比して消費電力は約１２と高い省エネ効果も得られました

進むＬＥＤの有効利用は省エネ等の地球温暖化対策だけではなく農業の分野にも大きな力となっているのですね

高shy電源との間に簡単なパルスshy生器を設置するだけでナノ秒以下の短周期でのパルス光化が

可能でnbspる

植物の生長特に光合成反応に対しては連続光よりもパルス光の方が光の利用効率が高いと考えら

れている 34）今後植物栽培におけるパルス光照射のメリットの大きさを定量的に確認する必要が

nbspるがパルスshy生器などの装置的なコストを上回る栽培効率向上が認められればＬＥＤはＬ

Ｄとともに非常に優れたパルス栽培光源ということができる

２４ 耐久性コンパクト

通常の使用条件で赤色ＬＥＤのランプ寿命は５万時間以上nbspりこれは１日 12 時間照明の植物工

場を 10 年以上稼shyさせる耐久性でnbspるさらにＬＥＤは形状が非常にコンパクトでnbspる

ことから光源部分の形状をかなり自由に設計できる例えば厚さ数ミリのパネル光源はもちろんの

ことさらに薄いシート状の光源や紐状の線光源なども可能でnbspるこうしたＬＥＤの耐久性やラン

プ形状の特徴は植物工場の光源ユニットを設計するうえで大きな自由度を提供する

3リーフレタス栽培試験

31 赤色青色ＬＥＤによる栽培試験

植物の光反応系の活性スペクトルに合わせ３種類のピーク波長（青色 450nm赤色 660 nm遠赤色

730nmshy光スペクトルは Fig 1 参照）を持つＬＥＤを選択しリーフレタスの水耕栽培を行った

ＬＥＤパネル（新光電子製）は45 x 45cm のゕルミフレームに 1000 個（25 列40 段）の砲弾型ＬＥＤ

を設置したもので列毎にピーク波長の変換光出力の調節ができるよう設計した（Fig 2）湛液式水

耕装置（新和製）を用い気温湿度ＣＯ2濃度をコントロールしたンキュベーター内でリーフレ

タス（品種レッドフゔヤー）を水耕栽培し生育に必要な光量と波長構成を調べた（Fig 3）56）

その結果リーフレタスは光合成有効光量子束密度（ＰＰＦＤ）で全光量として 100μmolｍ-2ｓ-

1青色光を８以上添加した赤色光を照射することにより自然光と同様の草型葉色を保ちつつ効

率良shy栽培できることが判明した（Fig 4）栽培中に青色光が不足すると節間と葉柄の伸長が促進

されいわゆる徒長症状を呈するしかしこの症状は赤色光量の増加によってnbspる程度回避でき

ることも見いだされた遠赤色光はこの条件でのリーフレタス栽培には必要なshy逆に草型を乱し

て生育を妨げることが示された

32 パルス光による栽培試験

前段で用いたＬＥＤパネル光源にパルスshy生器を備えた電源装置（新光電子製）を接続し照射

光を周期 10μｓ～10ｍｓデューテゖー比（ＤＴ比明期時間周期）10～50の間で変化させリーフ

レタス苗を栽培した 7）

まずパルス光の消費電力を 100Ｗｍ-2ＤＴ比を 50に固定し周期を 10μｓから 10ｍｓに変化させ

てリーフレタス苗を 20 日間栽培したその結果周期を 100μｓ以下のパルス光にした場合連続光に比

べ約 20の生育促進効果が認められ（Fig 5 左図）短周期のパルス光がリーフレタスの生育に好影響

を与えることが判明した次にパルス光の周期を 10μｓに固定しＤＴ比を 10から 50まで変化さ

せた明期の消費電力を調節し暗期を含めた平均消費電力を 100Ｗｍ-2 になるように設定した結果

はＤＴ比 25から 50で生育が促進されるのに対しＤＴ比 10ではパルス化の効果はほとんど失わ

れることが明らかとなった（Fig5)

３３ 水冷式ＬＥＤパネル光源を用いた栽培試験

ＬＥＤの外部量子効率は現在高効率とされる赤色光ＬＥＤでも 22程度でnbspる残りの電気エ

ネルギーの大部分はチップ自身のshy熱として消耗すると考えられるそこで Fig 6 に示す構造の水冷

式ＬＥＤパネル光源（ピーク波長 660nm）を試作したこのパネルではＬＥＤ集積基盤のnbsp側を

冷却水で除熱することによりパネル温度を一定に保ちshy光面側への熱の移動をほとんど遮断するこ

とができるその上ＬＥＤチップのｐ-ｎ接合部の温度上昇を防ぎ定格電流の約５倍の順方向電流で

駆動してもshy光効率の低下や際立った寿命の短縮は認められなかった

このＬＥＤパネルを Fig 7 に示す閉鎖型栽培装置に組み込みリーフレタスの栽培を試みたこの栽

培装置ではＬＥＤパネルからの熱の放出がないことからＬＥＤパネルの周囲を完全に密閉することが

できる栽培室のまわりを白色ゕクリル板で密閉した結果放射された光は栽培室からほとんど漏れる

ことがなshyその結果栽培ボード上のＰＰＦＤは飛躍的に増加した（Fig 8）またＬＥＤパネルの

水冷により栽培室の温度上昇は完全に防ぐことができた冷却媒体に水を使うことにより通常のエ

ゕコン空調と比べてシステムの温度制御にかかる電力を約半分に低減することができたまた栽培した

リーフレタスの生育状態も良好だった 8）

4特定の植物生理に対する影響

光合成反応を介して光は植物のエネルギー源になると同時にshy芽展葉草丈伸長花芽形成な

ど植物組織や器官の分化形態形成にも深shy関わっているレタス以外の色々な植物にＬＥＤ青色光

赤色光遠赤色光を照射し植物の器官分化形態形成にどのような影響を与えるかを調べたところ

種々の興味深い現象が認められた 5）

たとえばコマツナとチンゲンサは同じゕブラナ科に属し分類学上ではかなり近縁の植物で

nbspるところが遠赤色光に対する反応は両者で異なりコマツナは遠赤色光に対して顕著な葉柄伸

長を示すが節間には全shy影響しなかった（Fig 9 上図）一方チンゲンサでは遠赤色光は節間

伸長のみに影響し葉柄伸長には影響しなかった（Fig 9 下図）またハツカダコンは赤色光のみで

地上部は正常な草型に生育するが根部の肥大には青色光の添加が不可欠でnbspった（Fig 10）

日長の変化による花芽形成にはフゖトクローム系の赤色光と遠赤色光が関わっているたとえばキ

クなど短日植物（昼時間の減shyによって開花を誘導する植物群）の長日処理（夜間照明によって昼時

間を延長させる処理）による花芽形成抑制に対しては赤色光が有効でnbspることが知られている

白色輪ギクを用いてＬＥＤ赤色光による花芽抑制効果を調査したところ通常の白熱電灯栽培に比較し

て消費電力を 70以上削減できることが明らかとなったその上収穫されたキクは品質的にも優れて

おりＬＥＤによるキク電照栽培のメリットを確認することができた 910）

5ＬＥＤ植物工場の可能性

植物栽培用光源としてのＬＥＤの最大の利点はコンパクトな装置で栽培植物の生長や特定の植物生

理を精密に制御できる点にnbspる例えば植物の植えつけボードからＬＥＤパネルまでの高さは栽

培する植物の最大草丈分程度を確保すればよshyレタスサラダナでnbspれば約 20cm通常のプ

ラグ苗では 10cm もとれば十分でnbspるそうした栽培ユニットを何層にも積み重ねることによりス

ペースを立体的に活用しコンパクトな栽培装置に床面積の数倍の栽培面積を確保することは容易で

nbspるまた栽培装置の小型化は温度管理のコストメリットも大きい

さらに栽培植物の生育ステージに合わせて照射波長や光量をプログラム制御することも容易で

nbspるその結果栽培期間の短縮や増収効果健苗育成効果などが期待できる高辻らはＬＥＤによ

るサラダナ栽培において明暗周期を短shyすることによって特に大きな増収効果が得られることを

報告している 11）また波長光量の制御により花芽形成や草型のコントロール 9）可食部やその中の

栄養成分の増量など 12）目的とする植物生理現象を必要なタミングで誘導することも可能でnbspる

このような植物栽培光源としてのＬＥＤのメリットを最大に利用するには太陽光を併用せず人工光

のみの完全制御型植物工場の方がＬＥＤには適していると考えている

電力コストの削減や栽培植物の生長生理の正確なコントロールへの期待が大きいＬＥＤ光源で

nbspるがまずその植物栽培光源としての性能やメリットをこれまで以上に定量的に把握することが必

要でnbspろう普及性のnbspる植物工場の開shyでの最大の課題はいかに野菜のトータルの生

産コストを下げるかに尽きると考えている生産コストの内建設費などのニシャルコストの削減と

電力費などランニングコストの削減は相反する場合が多いいかに低コストの資材を使って電力を使

わない栽培システムを作るか両者のかね合いで装置の備えるべき機能性能を取捨選択し栽培装置

全体としてコストと性能のバランスのとれた栽培システムを構築していshyことが必要でnbspる

6おわりに

人工光による植物栽培はこれまで照明用のランプを適用して行われてきたそれら照明用ランプが照

射する光は基本的には人の目に明るい波長特性を持ったものでnbspり植物の利用特性に沿ったも

のではない正確に植物の好みに合ったいうなれば植物にオシ光環境はＬＥＤやＬＤを光源と

することによって初めて実現されるといえる植物の光利用特性をふまえ植物生長および種々の植物

生理現象を正確に制御できる機能を持った栽培装置をＬＥＤさらにはＬＤを光源として用いること

によってシステム化したいと考えている

１）高辻正基植物工場の基礎と実際（裳華房 1996）p85 ２）渡辺博之ＬＥＤ光源の植物栽培利用（植物工場実用化ビジネス研究部会資料 1995） ３）岩波洋造光合成の世界（講談社ブルーバックス）p152 ４）高辻正基野菜工場（丸善 1986）p127 ５）渡辺博之田中史宏遠藤shy弘ら 園芸学会誌 64(別 1)(1995)390 ６）渡辺博之田中史宏ら日本植物工場学会平成 7 年度大会要旨（1995）p17 ７）渡辺博之田中史宏遠藤shy弘日本植物工場学会平成 7 年度大会要旨（1995）p19 ８）渡辺博之田中史宏吉野徹日本植物工場学会平成 8 年度大会要旨（1996）p23 ９）渡辺博之河合成典ら 園芸学会誌 65(別 1)（1996）452 １０）渡辺博之河合成典ら 園芸学会誌 65(別 2)（1996）568 １１）高辻正基釜谷慎太郎榎本岳夫植物工場学会誌 8(2) （1996）119 １２）田中史宏渡辺博之遠藤shy弘ら園芸学会誌 64(別 1) （1995）392

環境ンフォメーション

ＬＥＤによるレタス栽培

太陽からの光が遮断される室内で効率よく植物を育てられるか

近年屋内で温度や湿度光（照明）等の環境条件を人工的に制御する事により農薬を使用せずに農作物を生産す

る技術が注目を浴びています

その太陽光の変わりに使用する光源として注目を浴びているのがＬＥＤ（発光ダオード）です従来光源として

考えられていた蛍光灯に比してＬＥＤを使用する事により消費電力を大幅に削減できる事が理由の一端に挙げられ

ます

県立中央農業高校（海老名市中新田）三年の岡崎仁美さん（18）がそのＬＥＤを使用しレタスを栽培する研究に

取り組みその研究成果が第五十二回日本学生科学賞県作品展で県知事賞に輝いています

その研究内容とは『蛍光灯より寿命が長く消費電力の少ないＬＥＤを使用する事により省エネかつ高品質な食

物を育てられるのでは』と着想しその有効性を実験しました

その内容は『赤』『青』『赤白混合』『紫外線』『赤外線』等様々な波長の 9 種類のＬＥＤの光を 1 日 16 時間

当てて2 週間レタスを栽培

その結果として『赤白混合』の光を当てたレタスが最も高品質に育ったそうですその上蛍光灯を使用しての栽培

に比して消費電力は約１２と高い省エネ効果も得られました

進むＬＥＤの有効利用は省エネ等の地球温暖化対策だけではなく農業の分野にも大きな力となっているのですね

32 パルス光による栽培試験

前段で用いたＬＥＤパネル光源にパルスshy生器を備えた電源装置（新光電子製）を接続し照射

光を周期 10μｓ～10ｍｓデューテゖー比（ＤＴ比明期時間周期）10～50の間で変化させリーフ

レタス苗を栽培した 7）

まずパルス光の消費電力を 100Ｗｍ-2ＤＴ比を 50に固定し周期を 10μｓから 10ｍｓに変化させ

てリーフレタス苗を 20 日間栽培したその結果周期を 100μｓ以下のパルス光にした場合連続光に比

べ約 20の生育促進効果が認められ（Fig 5 左図）短周期のパルス光がリーフレタスの生育に好影響

を与えることが判明した次にパルス光の周期を 10μｓに固定しＤＴ比を 10から 50まで変化さ

せた明期の消費電力を調節し暗期を含めた平均消費電力を 100Ｗｍ-2 になるように設定した結果

はＤＴ比 25から 50で生育が促進されるのに対しＤＴ比 10ではパルス化の効果はほとんど失わ

れることが明らかとなった（Fig5)

３３ 水冷式ＬＥＤパネル光源を用いた栽培試験

ＬＥＤの外部量子効率は現在高効率とされる赤色光ＬＥＤでも 22程度でnbspる残りの電気エ

ネルギーの大部分はチップ自身のshy熱として消耗すると考えられるそこで Fig 6 に示す構造の水冷

式ＬＥＤパネル光源（ピーク波長 660nm）を試作したこのパネルではＬＥＤ集積基盤のnbsp側を

冷却水で除熱することによりパネル温度を一定に保ちshy光面側への熱の移動をほとんど遮断するこ

とができるその上ＬＥＤチップのｐ-ｎ接合部の温度上昇を防ぎ定格電流の約５倍の順方向電流で

駆動してもshy光効率の低下や際立った寿命の短縮は認められなかった

このＬＥＤパネルを Fig 7 に示す閉鎖型栽培装置に組み込みリーフレタスの栽培を試みたこの栽

培装置ではＬＥＤパネルからの熱の放出がないことからＬＥＤパネルの周囲を完全に密閉することが

できる栽培室のまわりを白色ゕクリル板で密閉した結果放射された光は栽培室からほとんど漏れる

ことがなshyその結果栽培ボード上のＰＰＦＤは飛躍的に増加した（Fig 8）またＬＥＤパネルの

水冷により栽培室の温度上昇は完全に防ぐことができた冷却媒体に水を使うことにより通常のエ

ゕコン空調と比べてシステムの温度制御にかかる電力を約半分に低減することができたまた栽培した

リーフレタスの生育状態も良好だった 8）

4特定の植物生理に対する影響

光合成反応を介して光は植物のエネルギー源になると同時にshy芽展葉草丈伸長花芽形成な

ど植物組織や器官の分化形態形成にも深shy関わっているレタス以外の色々な植物にＬＥＤ青色光

赤色光遠赤色光を照射し植物の器官分化形態形成にどのような影響を与えるかを調べたところ

種々の興味深い現象が認められた 5）

たとえばコマツナとチンゲンサは同じゕブラナ科に属し分類学上ではかなり近縁の植物で

nbspるところが遠赤色光に対する反応は両者で異なりコマツナは遠赤色光に対して顕著な葉柄伸

長を示すが節間には全shy影響しなかった（Fig 9 上図）一方チンゲンサでは遠赤色光は節間

伸長のみに影響し葉柄伸長には影響しなかった（Fig 9 下図）またハツカダコンは赤色光のみで

地上部は正常な草型に生育するが根部の肥大には青色光の添加が不可欠でnbspった（Fig 10）

日長の変化による花芽形成にはフゖトクローム系の赤色光と遠赤色光が関わっているたとえばキ

クなど短日植物（昼時間の減shyによって開花を誘導する植物群）の長日処理（夜間照明によって昼時

間を延長させる処理）による花芽形成抑制に対しては赤色光が有効でnbspることが知られている

白色輪ギクを用いてＬＥＤ赤色光による花芽抑制効果を調査したところ通常の白熱電灯栽培に比較し

て消費電力を 70以上削減できることが明らかとなったその上収穫されたキクは品質的にも優れて

おりＬＥＤによるキク電照栽培のメリットを確認することができた 910）

5ＬＥＤ植物工場の可能性

植物栽培用光源としてのＬＥＤの最大の利点はコンパクトな装置で栽培植物の生長や特定の植物生

理を精密に制御できる点にnbspる例えば植物の植えつけボードからＬＥＤパネルまでの高さは栽

培する植物の最大草丈分程度を確保すればよshyレタスサラダナでnbspれば約 20cm通常のプ

ラグ苗では 10cm もとれば十分でnbspるそうした栽培ユニットを何層にも積み重ねることによりス

ペースを立体的に活用しコンパクトな栽培装置に床面積の数倍の栽培面積を確保することは容易で

nbspるまた栽培装置の小型化は温度管理のコストメリットも大きい

さらに栽培植物の生育ステージに合わせて照射波長や光量をプログラム制御することも容易で

nbspるその結果栽培期間の短縮や増収効果健苗育成効果などが期待できる高辻らはＬＥＤによ

るサラダナ栽培において明暗周期を短shyすることによって特に大きな増収効果が得られることを

報告している 11）また波長光量の制御により花芽形成や草型のコントロール 9）可食部やその中の

栄養成分の増量など 12）目的とする植物生理現象を必要なタミングで誘導することも可能でnbspる

このような植物栽培光源としてのＬＥＤのメリットを最大に利用するには太陽光を併用せず人工光

のみの完全制御型植物工場の方がＬＥＤには適していると考えている

電力コストの削減や栽培植物の生長生理の正確なコントロールへの期待が大きいＬＥＤ光源で

nbspるがまずその植物栽培光源としての性能やメリットをこれまで以上に定量的に把握することが必

要でnbspろう普及性のnbspる植物工場の開shyでの最大の課題はいかに野菜のトータルの生

産コストを下げるかに尽きると考えている生産コストの内建設費などのニシャルコストの削減と

電力費などランニングコストの削減は相反する場合が多いいかに低コストの資材を使って電力を使

わない栽培システムを作るか両者のかね合いで装置の備えるべき機能性能を取捨選択し栽培装置

全体としてコストと性能のバランスのとれた栽培システムを構築していshyことが必要でnbspる

6おわりに

人工光による植物栽培はこれまで照明用のランプを適用して行われてきたそれら照明用ランプが照

射する光は基本的には人の目に明るい波長特性を持ったものでnbspり植物の利用特性に沿ったも

のではない正確に植物の好みに合ったいうなれば植物にオシ光環境はＬＥＤやＬＤを光源と

することによって初めて実現されるといえる植物の光利用特性をふまえ植物生長および種々の植物

生理現象を正確に制御できる機能を持った栽培装置をＬＥＤさらにはＬＤを光源として用いること

によってシステム化したいと考えている

１）高辻正基植物工場の基礎と実際（裳華房 1996）p85 ２）渡辺博之ＬＥＤ光源の植物栽培利用（植物工場実用化ビジネス研究部会資料 1995） ３）岩波洋造光合成の世界（講談社ブルーバックス）p152 ４）高辻正基野菜工場（丸善 1986）p127 ５）渡辺博之田中史宏遠藤shy弘ら 園芸学会誌 64(別 1)(1995)390 ６）渡辺博之田中史宏ら日本植物工場学会平成 7 年度大会要旨（1995）p17 ７）渡辺博之田中史宏遠藤shy弘日本植物工場学会平成 7 年度大会要旨（1995）p19 ８）渡辺博之田中史宏吉野徹日本植物工場学会平成 8 年度大会要旨（1996）p23 ９）渡辺博之河合成典ら 園芸学会誌 65(別 1)（1996）452 １０）渡辺博之河合成典ら 園芸学会誌 65(別 2)（1996）568 １１）高辻正基釜谷慎太郎榎本岳夫植物工場学会誌 8(2) （1996）119 １２）田中史宏渡辺博之遠藤shy弘ら園芸学会誌 64(別 1) （1995）392

環境ンフォメーション

ＬＥＤによるレタス栽培

太陽からの光が遮断される室内で効率よく植物を育てられるか

近年屋内で温度や湿度光（照明）等の環境条件を人工的に制御する事により農薬を使用せずに農作物を生産す

る技術が注目を浴びています

その太陽光の変わりに使用する光源として注目を浴びているのがＬＥＤ（発光ダオード）です従来光源として

考えられていた蛍光灯に比してＬＥＤを使用する事により消費電力を大幅に削減できる事が理由の一端に挙げられ

ます

県立中央農業高校（海老名市中新田）三年の岡崎仁美さん（18）がそのＬＥＤを使用しレタスを栽培する研究に

取り組みその研究成果が第五十二回日本学生科学賞県作品展で県知事賞に輝いています

その研究内容とは『蛍光灯より寿命が長く消費電力の少ないＬＥＤを使用する事により省エネかつ高品質な食

物を育てられるのでは』と着想しその有効性を実験しました

その内容は『赤』『青』『赤白混合』『紫外線』『赤外線』等様々な波長の 9 種類のＬＥＤの光を 1 日 16 時間

当てて2 週間レタスを栽培

その結果として『赤白混合』の光を当てたレタスが最も高品質に育ったそうですその上蛍光灯を使用しての栽培

に比して消費電力は約１２と高い省エネ効果も得られました

進むＬＥＤの有効利用は省エネ等の地球温暖化対策だけではなく農業の分野にも大きな力となっているのですね

３３ 水冷式ＬＥＤパネル光源を用いた栽培試験

ＬＥＤの外部量子効率は現在高効率とされる赤色光ＬＥＤでも 22程度でnbspる残りの電気エ

ネルギーの大部分はチップ自身のshy熱として消耗すると考えられるそこで Fig 6 に示す構造の水冷

式ＬＥＤパネル光源（ピーク波長 660nm）を試作したこのパネルではＬＥＤ集積基盤のnbsp側を

冷却水で除熱することによりパネル温度を一定に保ちshy光面側への熱の移動をほとんど遮断するこ

とができるその上ＬＥＤチップのｐ-ｎ接合部の温度上昇を防ぎ定格電流の約５倍の順方向電流で

駆動してもshy光効率の低下や際立った寿命の短縮は認められなかった

このＬＥＤパネルを Fig 7 に示す閉鎖型栽培装置に組み込みリーフレタスの栽培を試みたこの栽

培装置ではＬＥＤパネルからの熱の放出がないことからＬＥＤパネルの周囲を完全に密閉することが

できる栽培室のまわりを白色ゕクリル板で密閉した結果放射された光は栽培室からほとんど漏れる

ことがなshyその結果栽培ボード上のＰＰＦＤは飛躍的に増加した（Fig 8）またＬＥＤパネルの

水冷により栽培室の温度上昇は完全に防ぐことができた冷却媒体に水を使うことにより通常のエ

ゕコン空調と比べてシステムの温度制御にかかる電力を約半分に低減することができたまた栽培した

リーフレタスの生育状態も良好だった 8）

4特定の植物生理に対する影響

光合成反応を介して光は植物のエネルギー源になると同時にshy芽展葉草丈伸長花芽形成な

ど植物組織や器官の分化形態形成にも深shy関わっているレタス以外の色々な植物にＬＥＤ青色光

赤色光遠赤色光を照射し植物の器官分化形態形成にどのような影響を与えるかを調べたところ

種々の興味深い現象が認められた 5）

たとえばコマツナとチンゲンサは同じゕブラナ科に属し分類学上ではかなり近縁の植物で

nbspるところが遠赤色光に対する反応は両者で異なりコマツナは遠赤色光に対して顕著な葉柄伸

長を示すが節間には全shy影響しなかった（Fig 9 上図）一方チンゲンサでは遠赤色光は節間

伸長のみに影響し葉柄伸長には影響しなかった（Fig 9 下図）またハツカダコンは赤色光のみで

地上部は正常な草型に生育するが根部の肥大には青色光の添加が不可欠でnbspった（Fig 10）

日長の変化による花芽形成にはフゖトクローム系の赤色光と遠赤色光が関わっているたとえばキ

クなど短日植物（昼時間の減shyによって開花を誘導する植物群）の長日処理（夜間照明によって昼時

間を延長させる処理）による花芽形成抑制に対しては赤色光が有効でnbspることが知られている

白色輪ギクを用いてＬＥＤ赤色光による花芽抑制効果を調査したところ通常の白熱電灯栽培に比較し

て消費電力を 70以上削減できることが明らかとなったその上収穫されたキクは品質的にも優れて

おりＬＥＤによるキク電照栽培のメリットを確認することができた 910）

5ＬＥＤ植物工場の可能性

植物栽培用光源としてのＬＥＤの最大の利点はコンパクトな装置で栽培植物の生長や特定の植物生

理を精密に制御できる点にnbspる例えば植物の植えつけボードからＬＥＤパネルまでの高さは栽

培する植物の最大草丈分程度を確保すればよshyレタスサラダナでnbspれば約 20cm通常のプ

ラグ苗では 10cm もとれば十分でnbspるそうした栽培ユニットを何層にも積み重ねることによりス

ペースを立体的に活用しコンパクトな栽培装置に床面積の数倍の栽培面積を確保することは容易で

nbspるまた栽培装置の小型化は温度管理のコストメリットも大きい

さらに栽培植物の生育ステージに合わせて照射波長や光量をプログラム制御することも容易で

nbspるその結果栽培期間の短縮や増収効果健苗育成効果などが期待できる高辻らはＬＥＤによ

るサラダナ栽培において明暗周期を短shyすることによって特に大きな増収効果が得られることを

報告している 11）また波長光量の制御により花芽形成や草型のコントロール 9）可食部やその中の

栄養成分の増量など 12）目的とする植物生理現象を必要なタミングで誘導することも可能でnbspる

このような植物栽培光源としてのＬＥＤのメリットを最大に利用するには太陽光を併用せず人工光

のみの完全制御型植物工場の方がＬＥＤには適していると考えている

電力コストの削減や栽培植物の生長生理の正確なコントロールへの期待が大きいＬＥＤ光源で

nbspるがまずその植物栽培光源としての性能やメリットをこれまで以上に定量的に把握することが必

要でnbspろう普及性のnbspる植物工場の開shyでの最大の課題はいかに野菜のトータルの生

産コストを下げるかに尽きると考えている生産コストの内建設費などのニシャルコストの削減と

電力費などランニングコストの削減は相反する場合が多いいかに低コストの資材を使って電力を使

わない栽培システムを作るか両者のかね合いで装置の備えるべき機能性能を取捨選択し栽培装置

全体としてコストと性能のバランスのとれた栽培システムを構築していshyことが必要でnbspる

6おわりに

人工光による植物栽培はこれまで照明用のランプを適用して行われてきたそれら照明用ランプが照

射する光は基本的には人の目に明るい波長特性を持ったものでnbspり植物の利用特性に沿ったも

のではない正確に植物の好みに合ったいうなれば植物にオシ光環境はＬＥＤやＬＤを光源と

することによって初めて実現されるといえる植物の光利用特性をふまえ植物生長および種々の植物

生理現象を正確に制御できる機能を持った栽培装置をＬＥＤさらにはＬＤを光源として用いること

によってシステム化したいと考えている

１）高辻正基植物工場の基礎と実際（裳華房 1996）p85 ２）渡辺博之ＬＥＤ光源の植物栽培利用（植物工場実用化ビジネス研究部会資料 1995） ３）岩波洋造光合成の世界（講談社ブルーバックス）p152 ４）高辻正基野菜工場（丸善 1986）p127 ５）渡辺博之田中史宏遠藤shy弘ら 園芸学会誌 64(別 1)(1995)390 ６）渡辺博之田中史宏ら日本植物工場学会平成 7 年度大会要旨（1995）p17 ７）渡辺博之田中史宏遠藤shy弘日本植物工場学会平成 7 年度大会要旨（1995）p19 ８）渡辺博之田中史宏吉野徹日本植物工場学会平成 8 年度大会要旨（1996）p23 ９）渡辺博之河合成典ら 園芸学会誌 65(別 1)（1996）452 １０）渡辺博之河合成典ら 園芸学会誌 65(別 2)（1996）568 １１）高辻正基釜谷慎太郎榎本岳夫植物工場学会誌 8(2) （1996）119 １２）田中史宏渡辺博之遠藤shy弘ら園芸学会誌 64(別 1) （1995）392

環境ンフォメーション

ＬＥＤによるレタス栽培

太陽からの光が遮断される室内で効率よく植物を育てられるか

近年屋内で温度や湿度光（照明）等の環境条件を人工的に制御する事により農薬を使用せずに農作物を生産す

る技術が注目を浴びています

その太陽光の変わりに使用する光源として注目を浴びているのがＬＥＤ（発光ダオード）です従来光源として

考えられていた蛍光灯に比してＬＥＤを使用する事により消費電力を大幅に削減できる事が理由の一端に挙げられ

ます

県立中央農業高校（海老名市中新田）三年の岡崎仁美さん（18）がそのＬＥＤを使用しレタスを栽培する研究に

取り組みその研究成果が第五十二回日本学生科学賞県作品展で県知事賞に輝いています

その研究内容とは『蛍光灯より寿命が長く消費電力の少ないＬＥＤを使用する事により省エネかつ高品質な食

物を育てられるのでは』と着想しその有効性を実験しました

その内容は『赤』『青』『赤白混合』『紫外線』『赤外線』等様々な波長の 9 種類のＬＥＤの光を 1 日 16 時間

当てて2 週間レタスを栽培

その結果として『赤白混合』の光を当てたレタスが最も高品質に育ったそうですその上蛍光灯を使用しての栽培

に比して消費電力は約１２と高い省エネ効果も得られました

進むＬＥＤの有効利用は省エネ等の地球温暖化対策だけではなく農業の分野にも大きな力となっているのですね

赤色光遠赤色光を照射し植物の器官分化形態形成にどのような影響を与えるかを調べたところ

種々の興味深い現象が認められた 5）

たとえばコマツナとチンゲンサは同じゕブラナ科に属し分類学上ではかなり近縁の植物で

nbspるところが遠赤色光に対する反応は両者で異なりコマツナは遠赤色光に対して顕著な葉柄伸

長を示すが節間には全shy影響しなかった（Fig 9 上図）一方チンゲンサでは遠赤色光は節間

伸長のみに影響し葉柄伸長には影響しなかった（Fig 9 下図）またハツカダコンは赤色光のみで

地上部は正常な草型に生育するが根部の肥大には青色光の添加が不可欠でnbspった（Fig 10）

日長の変化による花芽形成にはフゖトクローム系の赤色光と遠赤色光が関わっているたとえばキ

クなど短日植物（昼時間の減shyによって開花を誘導する植物群）の長日処理（夜間照明によって昼時

間を延長させる処理）による花芽形成抑制に対しては赤色光が有効でnbspることが知られている

白色輪ギクを用いてＬＥＤ赤色光による花芽抑制効果を調査したところ通常の白熱電灯栽培に比較し

て消費電力を 70以上削減できることが明らかとなったその上収穫されたキクは品質的にも優れて

おりＬＥＤによるキク電照栽培のメリットを確認することができた 910）

5ＬＥＤ植物工場の可能性

植物栽培用光源としてのＬＥＤの最大の利点はコンパクトな装置で栽培植物の生長や特定の植物生

理を精密に制御できる点にnbspる例えば植物の植えつけボードからＬＥＤパネルまでの高さは栽

培する植物の最大草丈分程度を確保すればよshyレタスサラダナでnbspれば約 20cm通常のプ

ラグ苗では 10cm もとれば十分でnbspるそうした栽培ユニットを何層にも積み重ねることによりス

ペースを立体的に活用しコンパクトな栽培装置に床面積の数倍の栽培面積を確保することは容易で

nbspるまた栽培装置の小型化は温度管理のコストメリットも大きい

さらに栽培植物の生育ステージに合わせて照射波長や光量をプログラム制御することも容易で

nbspるその結果栽培期間の短縮や増収効果健苗育成効果などが期待できる高辻らはＬＥＤによ

るサラダナ栽培において明暗周期を短shyすることによって特に大きな増収効果が得られることを

報告している 11）また波長光量の制御により花芽形成や草型のコントロール 9）可食部やその中の

栄養成分の増量など 12）目的とする植物生理現象を必要なタミングで誘導することも可能でnbspる

このような植物栽培光源としてのＬＥＤのメリットを最大に利用するには太陽光を併用せず人工光

のみの完全制御型植物工場の方がＬＥＤには適していると考えている

電力コストの削減や栽培植物の生長生理の正確なコントロールへの期待が大きいＬＥＤ光源で

nbspるがまずその植物栽培光源としての性能やメリットをこれまで以上に定量的に把握することが必

要でnbspろう普及性のnbspる植物工場の開shyでの最大の課題はいかに野菜のトータルの生

産コストを下げるかに尽きると考えている生産コストの内建設費などのニシャルコストの削減と

電力費などランニングコストの削減は相反する場合が多いいかに低コストの資材を使って電力を使

わない栽培システムを作るか両者のかね合いで装置の備えるべき機能性能を取捨選択し栽培装置

全体としてコストと性能のバランスのとれた栽培システムを構築していshyことが必要でnbspる

6おわりに

人工光による植物栽培はこれまで照明用のランプを適用して行われてきたそれら照明用ランプが照

射する光は基本的には人の目に明るい波長特性を持ったものでnbspり植物の利用特性に沿ったも

のではない正確に植物の好みに合ったいうなれば植物にオシ光環境はＬＥＤやＬＤを光源と

することによって初めて実現されるといえる植物の光利用特性をふまえ植物生長および種々の植物

生理現象を正確に制御できる機能を持った栽培装置をＬＥＤさらにはＬＤを光源として用いること

によってシステム化したいと考えている

１）高辻正基植物工場の基礎と実際（裳華房 1996）p85 ２）渡辺博之ＬＥＤ光源の植物栽培利用（植物工場実用化ビジネス研究部会資料 1995） ３）岩波洋造光合成の世界（講談社ブルーバックス）p152 ４）高辻正基野菜工場（丸善 1986）p127 ５）渡辺博之田中史宏遠藤shy弘ら 園芸学会誌 64(別 1)(1995)390 ６）渡辺博之田中史宏ら日本植物工場学会平成 7 年度大会要旨（1995）p17 ７）渡辺博之田中史宏遠藤shy弘日本植物工場学会平成 7 年度大会要旨（1995）p19 ８）渡辺博之田中史宏吉野徹日本植物工場学会平成 8 年度大会要旨（1996）p23 ９）渡辺博之河合成典ら 園芸学会誌 65(別 1)（1996）452 １０）渡辺博之河合成典ら 園芸学会誌 65(別 2)（1996）568 １１）高辻正基釜谷慎太郎榎本岳夫植物工場学会誌 8(2) （1996）119 １２）田中史宏渡辺博之遠藤shy弘ら園芸学会誌 64(別 1) （1995）392

環境ンフォメーション

ＬＥＤによるレタス栽培

太陽からの光が遮断される室内で効率よく植物を育てられるか

近年屋内で温度や湿度光（照明）等の環境条件を人工的に制御する事により農薬を使用せずに農作物を生産す

る技術が注目を浴びています

その太陽光の変わりに使用する光源として注目を浴びているのがＬＥＤ（発光ダオード）です従来光源として

考えられていた蛍光灯に比してＬＥＤを使用する事により消費電力を大幅に削減できる事が理由の一端に挙げられ

ます

県立中央農業高校（海老名市中新田）三年の岡崎仁美さん（18）がそのＬＥＤを使用しレタスを栽培する研究に

取り組みその研究成果が第五十二回日本学生科学賞県作品展で県知事賞に輝いています

その研究内容とは『蛍光灯より寿命が長く消費電力の少ないＬＥＤを使用する事により省エネかつ高品質な食

物を育てられるのでは』と着想しその有効性を実験しました

その内容は『赤』『青』『赤白混合』『紫外線』『赤外線』等様々な波長の 9 種類のＬＥＤの光を 1 日 16 時間

当てて2 週間レタスを栽培

その結果として『赤白混合』の光を当てたレタスが最も高品質に育ったそうですその上蛍光灯を使用しての栽培

に比して消費電力は約１２と高い省エネ効果も得られました

進むＬＥＤの有効利用は省エネ等の地球温暖化対策だけではなく農業の分野にも大きな力となっているのですね

報告している 11）また波長光量の制御により花芽形成や草型のコントロール 9）可食部やその中の

栄養成分の増量など 12）目的とする植物生理現象を必要なタミングで誘導することも可能でnbspる

このような植物栽培光源としてのＬＥＤのメリットを最大に利用するには太陽光を併用せず人工光

のみの完全制御型植物工場の方がＬＥＤには適していると考えている

電力コストの削減や栽培植物の生長生理の正確なコントロールへの期待が大きいＬＥＤ光源で

nbspるがまずその植物栽培光源としての性能やメリットをこれまで以上に定量的に把握することが必

要でnbspろう普及性のnbspる植物工場の開shyでの最大の課題はいかに野菜のトータルの生

産コストを下げるかに尽きると考えている生産コストの内建設費などのニシャルコストの削減と

電力費などランニングコストの削減は相反する場合が多いいかに低コストの資材を使って電力を使

わない栽培システムを作るか両者のかね合いで装置の備えるべき機能性能を取捨選択し栽培装置

全体としてコストと性能のバランスのとれた栽培システムを構築していshyことが必要でnbspる

6おわりに

人工光による植物栽培はこれまで照明用のランプを適用して行われてきたそれら照明用ランプが照

射する光は基本的には人の目に明るい波長特性を持ったものでnbspり植物の利用特性に沿ったも

のではない正確に植物の好みに合ったいうなれば植物にオシ光環境はＬＥＤやＬＤを光源と

することによって初めて実現されるといえる植物の光利用特性をふまえ植物生長および種々の植物

生理現象を正確に制御できる機能を持った栽培装置をＬＥＤさらにはＬＤを光源として用いること

によってシステム化したいと考えている

１）高辻正基植物工場の基礎と実際（裳華房 1996）p85 ２）渡辺博之ＬＥＤ光源の植物栽培利用（植物工場実用化ビジネス研究部会資料 1995） ３）岩波洋造光合成の世界（講談社ブルーバックス）p152 ４）高辻正基野菜工場（丸善 1986）p127 ５）渡辺博之田中史宏遠藤shy弘ら 園芸学会誌 64(別 1)(1995)390 ６）渡辺博之田中史宏ら日本植物工場学会平成 7 年度大会要旨（1995）p17 ７）渡辺博之田中史宏遠藤shy弘日本植物工場学会平成 7 年度大会要旨（1995）p19 ８）渡辺博之田中史宏吉野徹日本植物工場学会平成 8 年度大会要旨（1996）p23 ９）渡辺博之河合成典ら 園芸学会誌 65(別 1)（1996）452 １０）渡辺博之河合成典ら 園芸学会誌 65(別 2)（1996）568 １１）高辻正基釜谷慎太郎榎本岳夫植物工場学会誌 8(2) （1996）119 １２）田中史宏渡辺博之遠藤shy弘ら園芸学会誌 64(別 1) （1995）392

環境ンフォメーション

ＬＥＤによるレタス栽培

太陽からの光が遮断される室内で効率よく植物を育てられるか

近年屋内で温度や湿度光（照明）等の環境条件を人工的に制御する事により農薬を使用せずに農作物を生産す

る技術が注目を浴びています

その太陽光の変わりに使用する光源として注目を浴びているのがＬＥＤ（発光ダオード）です従来光源として

考えられていた蛍光灯に比してＬＥＤを使用する事により消費電力を大幅に削減できる事が理由の一端に挙げられ

ます

県立中央農業高校（海老名市中新田）三年の岡崎仁美さん（18）がそのＬＥＤを使用しレタスを栽培する研究に

取り組みその研究成果が第五十二回日本学生科学賞県作品展で県知事賞に輝いています

その研究内容とは『蛍光灯より寿命が長く消費電力の少ないＬＥＤを使用する事により省エネかつ高品質な食

物を育てられるのでは』と着想しその有効性を実験しました

その内容は『赤』『青』『赤白混合』『紫外線』『赤外線』等様々な波長の 9 種類のＬＥＤの光を 1 日 16 時間

当てて2 週間レタスを栽培

その結果として『赤白混合』の光を当てたレタスが最も高品質に育ったそうですその上蛍光灯を使用しての栽培

に比して消費電力は約１２と高い省エネ効果も得られました

進むＬＥＤの有効利用は省エネ等の地球温暖化対策だけではなく農業の分野にも大きな力となっているのですね

環境ンフォメーション

ＬＥＤによるレタス栽培

太陽からの光が遮断される室内で効率よく植物を育てられるか

近年屋内で温度や湿度光（照明）等の環境条件を人工的に制御する事により農薬を使用せずに農作物を生産す

る技術が注目を浴びています

その太陽光の変わりに使用する光源として注目を浴びているのがＬＥＤ（発光ダオード）です従来光源として

考えられていた蛍光灯に比してＬＥＤを使用する事により消費電力を大幅に削減できる事が理由の一端に挙げられ

ます

県立中央農業高校（海老名市中新田）三年の岡崎仁美さん（18）がそのＬＥＤを使用しレタスを栽培する研究に

取り組みその研究成果が第五十二回日本学生科学賞県作品展で県知事賞に輝いています

その研究内容とは『蛍光灯より寿命が長く消費電力の少ないＬＥＤを使用する事により省エネかつ高品質な食

物を育てられるのでは』と着想しその有効性を実験しました

その内容は『赤』『青』『赤白混合』『紫外線』『赤外線』等様々な波長の 9 種類のＬＥＤの光を 1 日 16 時間

当てて2 週間レタスを栽培

その結果として『赤白混合』の光を当てたレタスが最も高品質に育ったそうですその上蛍光灯を使用しての栽培

に比して消費電力は約１２と高い省エネ効果も得られました

進むＬＥＤの有効利用は省エネ等の地球温暖化対策だけではなく農業の分野にも大きな力となっているのですね

LED の光による栽培テスト中のレタス

LED 照明器ただいま点灯試験中

正面からは明るすぎるので背面から撮影してます

器具の外観

下から 上から

斜め上から 各部の測定中

今回の回路図です電流安定回路付

LED 赤３０個青１０個合計４０個 直列に接続

諸元の測定値

上段電流安定回路データ

下段電流安定回路付きのデータ 大きくuarrしてみて

上記測定器の各窓の割り当て表示内容です

今回の点灯方式の特徴

①部品点数が少なく故障が少ない安価

②商用１００V 電源でそのまま点灯出来るほぼ限界

③本方式での効率はほぼ限界に近いと推定される

④力率はかなり低いほぼ０６（②と③項譲歩で改善可

ついに発売 新型植物工場用 LED ランプ

これまでの 10 倍の効果を発揮 すべてパルス点灯します

基板外観パルスドラバー

付

赤色 LED64 個 青色 LED6

個

スタンド型仕様品

660nm 2800mcd

の超高輝度 LED ランプを

使用しています

上段8 連タプ

下段3 連タプ

3 連タプスタンド型

パルス点灯回路内蔵 照射光波長 ６６０ｎｍ ４７０ｎｍ

「植物工場用 LED ランプ２」の仕様 代表値

下から 上から

斜め上から 各部の測定中

今回の回路図です電流安定回路付

LED 赤３０個青１０個合計４０個 直列に接続

諸元の測定値

上段電流安定回路データ

下段電流安定回路付きのデータ 大きくuarrしてみて

上記測定器の各窓の割り当て表示内容です

今回の点灯方式の特徴

①部品点数が少なく故障が少ない安価

②商用１００V 電源でそのまま点灯出来るほぼ限界

③本方式での効率はほぼ限界に近いと推定される

④力率はかなり低いほぼ０６（②と③項譲歩で改善可

ついに発売 新型植物工場用 LED ランプ

これまでの 10 倍の効果を発揮 すべてパルス点灯します

基板外観パルスドラバー

付

赤色 LED64 個 青色 LED6

個

スタンド型仕様品

660nm 2800mcd

の超高輝度 LED ランプを

使用しています

上段8 連タプ

下段3 連タプ

3 連タプスタンド型

パルス点灯回路内蔵 照射光波長 ６６０ｎｍ ４７０ｎｍ

「植物工場用 LED ランプ２」の仕様 代表値

LED 赤３０個青１０個合計４０個 直列に接続

諸元の測定値

上段電流安定回路データ

下段電流安定回路付きのデータ 大きくuarrしてみて

上記測定器の各窓の割り当て表示内容です

今回の点灯方式の特徴

①部品点数が少なく故障が少ない安価

②商用１００V 電源でそのまま点灯出来るほぼ限界

③本方式での効率はほぼ限界に近いと推定される

④力率はかなり低いほぼ０６（②と③項譲歩で改善可

ついに発売 新型植物工場用 LED ランプ

これまでの 10 倍の効果を発揮 すべてパルス点灯します

基板外観パルスドラバー

付

赤色 LED64 個 青色 LED6

個

スタンド型仕様品

660nm 2800mcd

の超高輝度 LED ランプを

使用しています

上段8 連タプ

下段3 連タプ

3 連タプスタンド型

パルス点灯回路内蔵 照射光波長 ６６０ｎｍ ４７０ｎｍ

「植物工場用 LED ランプ２」の仕様 代表値

今回の点灯方式の特徴

①部品点数が少なく故障が少ない安価

②商用１００V 電源でそのまま点灯出来るほぼ限界

③本方式での効率はほぼ限界に近いと推定される

④力率はかなり低いほぼ０６（②と③項譲歩で改善可

ついに発売 新型植物工場用 LED ランプ

これまでの 10 倍の効果を発揮 すべてパルス点灯します

基板外観パルスドラバー

付

赤色 LED64 個 青色 LED6

個

スタンド型仕様品

660nm 2800mcd

の超高輝度 LED ランプを

使用しています

上段8 連タプ

下段3 連タプ

3 連タプスタンド型

パルス点灯回路内蔵 照射光波長 ６６０ｎｍ ４７０ｎｍ

「植物工場用 LED ランプ２」の仕様 代表値

ついに発売 新型植物工場用 LED ランプ

これまでの 10 倍の効果を発揮 すべてパルス点灯します

基板外観パルスドラバー

付

赤色 LED64 個 青色 LED6

個

スタンド型仕様品

660nm 2800mcd

の超高輝度 LED ランプを

使用しています

上段8 連タプ

下段3 連タプ

3 連タプスタンド型

パルス点灯回路内蔵 照射光波長 ６６０ｎｍ ４７０ｎｍ

「植物工場用 LED ランプ２」の仕様 代表値

赤色ＬＥ

Ｄ

使用数量 ６４ 個

中心波長 ６６０ ｎｍ

輝度 ２８００ ｍｃｄ

使用ＬＥＤ一個あたりの

出力

(輝度と波長から算出)

６ ｍＷ

使用ＬＥＤの半値角 ３０ ＤＥＧ

青色ＬＥ

Ｄ

使用数量 ６ 個

中心波長 ４７０ ｎｍ

輝度 ５８００ ｍｃｄ

使用ＬＥＤ一個あたりの

出力

(輝度と波長から算出)

１２ ｍＷ

使用ＬＥＤの半値角 ６０ ＤＥＧ

パルス点

灯

点灯時間 ２００ μｓｅ

ｃ

消灯時間 ２００ μｓｅ

ｃ

電源 コネクタ ＤＣジャック 外形 φ５５ ピン径 φ

２１

電源電圧 １２ Ｖ

消費電流 ０４ Ａ

サズ 外形 幅８５０times奥１０００times高２５０ ｍｍ

取り付け穴 基板 4 隅から 5mm の位置 M4 ネジ 4 箇

所

質量 ５４ ｇ

防湿処理 コーテゖング剤（ＬＯＣＴＩＴＥ２３５５２）にて全面防湿処理

付属品 ＡＣゕダプター １２Ｖ １０Ａ ８０ｇ

価格表 「自作用プリント基板」以外は AC ゕダプタ込みの値段です

植物工場用ＬＥＤランプ２

標準タプ 赤色ＬＥＤ６４個 青色ＬＥＤ６個タプです ２４５００円

標準タプ

スタンド型

標準タプ LED ランプのスタンド仕様です ３００００円

２倍サズ 赤色ＬＥＤ１２８個 青色ＬＥＤ１２個タプです

販売終了

３３０００円

３連タプ ステンレス製ケースに標準タプを３台搭載したタプ

です

(写真) (4 隅に吊下金具がついています)

５３０００円

３連タプ

スタンド型

３連タプ LED ランプのスタンド仕様です(写真) ５８０００円

８連タプ スチール製ケースに標準タプを８台搭載 (写真)

したタプです

３００times６００の範囲にＬＥＤ光を照射します

プラグトレ等での栽培用です

１３７０００

円

自作キット専用基板など

標準タプ

自作キット

赤色ＬＥＤ６４個 青色ＬＥＤ６個タプの自作キット １７０００円

自作用

プリント基

板

LED 以外の部品付属 チップ部品実装済み ＡＣゕダプ

タ別

５０００円

ＡＣゕダプ

タ

１２Ｖ１Ａ （秋月電子通商さんからの購入品です） １０００円

お問合せご注文フォーム

標準タプ 赤色ＬＥＤ６４個 青色ＬＥＤ６個タプです ２４５００円

標準タプ

スタンド型

標準タプ LED ランプのスタンド仕様です ３００００円

２倍サズ 赤色ＬＥＤ１２８個 青色ＬＥＤ１２個タプです

販売終了

３３０００円

３連タプ ステンレス製ケースに標準タプを３台搭載したタプ

です

(写真) (4 隅に吊下金具がついています)

５３０００円

３連タプ

スタンド型

３連タプ LED ランプのスタンド仕様です(写真) ５８０００円

８連タプ スチール製ケースに標準タプを８台搭載 (写真)

したタプです

３００times６００の範囲にＬＥＤ光を照射します

プラグトレ等での栽培用です

１３７０００

円

自作キット専用基板など

標準タプ

自作キット

赤色ＬＥＤ６４個 青色ＬＥＤ６個タプの自作キット １７０００円

自作用

プリント基

板

LED 以外の部品付属 チップ部品実装済み ＡＣゕダプ

タ別

５０００円

ＡＣゕダプ

タ

１２Ｖ１Ａ （秋月電子通商さんからの購入品です） １０００円

お問合せご注文フォーム

パルスドラバー写真 パルスドラバーの仕様

入力 コネクター DC ジャック

外形 φ５５内径

２１

ｍｍ

電圧 ５～１５ V

電流 ５ A

出力 コネクター DC プラグ

外形 φ５５内径

２１

ｍｍ

電圧 入力に同じ V

電流 力に同じ Ａ

周波数 約２５ ｋＨ

ｚ

デューテゖ

ー

約５０

質量 １７ ｇ

販売価格 ４０００ 円

24V 仕様 販売価

格

４５００ 円

販売終了です

注意「植物工場用 LED ランプ」は販売終了しました

「植物工場用 LED ランプ２」の新型プリント基板に変わりまし

た

サズ １００times１７０ times１６ｔ

新型はサズが半分(１００times８５)でパルスドラバーつき

材質 ガラスエポキシ基板 FR4

レジスト色 白色

付属部品 チップ抵抗２２０Ω３２個２７０Ω６４個 切替 SW１個 DC

ジャック１個

質量 基板＋付属部品で７０ｇ

販売価格 ５０００円 送料別

AC ゕダプター別

売り

１０００円 190g （AC ゕダプターは秋月電子さんでも購入でき

ます)

発送は郵便局の

「EXPACK」が 500 円 （手渡しで受け取れる荷物追跡が可能）

「定形外郵便」が 100g140 円 150g200 円 250g240 円 500g390 円

青色点灯 赤色点灯 取り付けネジ部

高輝度 LED１２８個使用 自動車のリゕフォグラン

プラリーバクのダスト

ランプにも使えるのでは

４隅には M4 取り付けネ

ジがあります

仕様

入力電圧 １２Ｖ Ｖ

入力電流 (赤)06A (青)約 12A Ａ

LED 数 １２８ 個

サズ １７０times１００ times３５ ｍｍ

電源 ＡＣ１００Ｖ５０６０Ｈｚ

取り付けネジ 基板 4 隅から 5mm の位置 M4 ネジ 4 箇所

赤 LED PARALight L-513LE 1200mcd 625nm 半値角 15 度

OptoSupply OSHR5111A-TU 14000mcd 625nm 半値角 15 度

青 LED SANYO SLP-0H118A 1200mcd468nm 半値角 40 度

防湿処理 LED ランプユニットは防湿防塵絶縁コーテゖング処理してあります

付属品 専用 AC ゕダプター付属

ランナップ

１ 赤色青色のスッチ切り替え式

２ 赤色青色同時点灯（パルスドラバーを併用してください）

３ 赤色のみ

４ 青色のみ

５ 白色のみ

上記の標準基板を組み合わせた大型システムも製作できます

大型システム構築する際は専用電源の製作もいたしますお問い合わせ下さい

使用する LED は改良のため同等品と変更されることがあります

LED ランプの色や色の組み合わせはゕレンジできますお問合せ下さい

左上段から 「赤のみ」 「赤青」 「赤青緑」

下段中 「白」

室内水耕栽培１ 植物育成 LED ラト

＜はじめに＞

天候に左右されないこと短期間での収穫無農薬の安全性など多くの長所があるために最近植物工場

が注目されていますすでに専業の会社から空き地利用型企業までかなりの数のプラントが立ち上げっ

て入るようです

植物育成ラトとして蛍光灯や LED などが個人レベルで使えるものとして数多く市販されているのでこ

れらを利用して実験的に植物工場もどきで水耕栽培によるレタス栽培が可能かどうかどれほどの期間

で収穫できるのかを試してみようと思います使用した照明は

L1植物育成国産 LED ラトフローラ（赤 96 個青 26 個付 LED ラトを 5 台併置）

L2植物育成中国製 LED ラトゕールユー（LED513 個付赤青＝101 で赤色が強い）

L3NEC 植物育成蛍光灯ビオレックス HG（20Wtimes２灯times２台）の 3 種です

また水耕栽培装置は「ため太郎」2 台と市販プランターにエゕポンプを使用したものの 3 台ですこれを

ホームセンターで買った金属棚の上においてセットしました設置場所にはまったく自然光の入らない

会社の通路です液体肥料としてはハポニカを使用

さて植物が光合成をして成長していくためには赤色と青色の波長の光が必要ですが

これら植物育成ラトは適正な波長の光を放つようにできているので問題はないと思いますが植物が成

長していくためには光合成を行う上である程度の光量が必要でその単位は光量子束密度（μmolm2S)で表

されるそうで育てる植物によって違いがありますが冬野菜なら 110 以上春秋野菜は 160 以上夏野菜

は 250 以上必要とのことです設定した状態で光量子計（藤原製作所 QMSS 型）を使って計ってみると

光源とプランターの間が 20cm と離れていることもありますが植物育成蛍光灯は 144（10cm では 260）

国産 LED フローラは 97（10cm では 160）中国産 LED ゕールユーは 37（10cm で 50）でした蛍光灯

以外は光量不足の感じがしますがレタスの生長にあわせその位置を変えるなどしてできるだけ光量を大

きくして成長過程を観察していきたいと思いますラトはすべて２４時間常時点灯です

ランナップ

１ 赤色青色のスッチ切り替え式

２ 赤色青色同時点灯（パルスドラバーを併用してください）

３ 赤色のみ

４ 青色のみ

５ 白色のみ

上記の標準基板を組み合わせた大型システムも製作できます

大型システム構築する際は専用電源の製作もいたしますお問い合わせ下さい

使用する LED は改良のため同等品と変更されることがあります

LED ランプの色や色の組み合わせはゕレンジできますお問合せ下さい

左上段から 「赤のみ」 「赤青」 「赤青緑」

下段中 「白」

室内水耕栽培１ 植物育成 LED ラト

＜はじめに＞

天候に左右されないこと短期間での収穫無農薬の安全性など多くの長所があるために最近植物工場

が注目されていますすでに専業の会社から空き地利用型企業までかなりの数のプラントが立ち上げっ

て入るようです

植物育成ラトとして蛍光灯や LED などが個人レベルで使えるものとして数多く市販されているのでこ

れらを利用して実験的に植物工場もどきで水耕栽培によるレタス栽培が可能かどうかどれほどの期間

で収穫できるのかを試してみようと思います使用した照明は

L1植物育成国産 LED ラトフローラ（赤 96 個青 26 個付 LED ラトを 5 台併置）

L2植物育成中国製 LED ラトゕールユー（LED513 個付赤青＝101 で赤色が強い）

L3NEC 植物育成蛍光灯ビオレックス HG（20Wtimes２灯times２台）の 3 種です

また水耕栽培装置は「ため太郎」2 台と市販プランターにエゕポンプを使用したものの 3 台ですこれを

ホームセンターで買った金属棚の上においてセットしました設置場所にはまったく自然光の入らない

会社の通路です液体肥料としてはハポニカを使用

さて植物が光合成をして成長していくためには赤色と青色の波長の光が必要ですが

これら植物育成ラトは適正な波長の光を放つようにできているので問題はないと思いますが植物が成

長していくためには光合成を行う上である程度の光量が必要でその単位は光量子束密度（μmolm2S)で表

されるそうで育てる植物によって違いがありますが冬野菜なら 110 以上春秋野菜は 160 以上夏野菜

は 250 以上必要とのことです設定した状態で光量子計（藤原製作所 QMSS 型）を使って計ってみると

光源とプランターの間が 20cm と離れていることもありますが植物育成蛍光灯は 144（10cm では 260）

国産 LED フローラは 97（10cm では 160）中国産 LED ゕールユーは 37（10cm で 50）でした蛍光灯

以外は光量不足の感じがしますがレタスの生長にあわせその位置を変えるなどしてできるだけ光量を大

きくして成長過程を観察していきたいと思いますラトはすべて２４時間常時点灯です

室内水耕栽培１ 植物育成 LED ラト

＜はじめに＞

天候に左右されないこと短期間での収穫無農薬の安全性など多くの長所があるために最近植物工場

が注目されていますすでに専業の会社から空き地利用型企業までかなりの数のプラントが立ち上げっ

て入るようです

植物育成ラトとして蛍光灯や LED などが個人レベルで使えるものとして数多く市販されているのでこ

れらを利用して実験的に植物工場もどきで水耕栽培によるレタス栽培が可能かどうかどれほどの期間

で収穫できるのかを試してみようと思います使用した照明は

L1植物育成国産 LED ラトフローラ（赤 96 個青 26 個付 LED ラトを 5 台併置）

L2植物育成中国製 LED ラトゕールユー（LED513 個付赤青＝101 で赤色が強い）

L3NEC 植物育成蛍光灯ビオレックス HG（20Wtimes２灯times２台）の 3 種です

また水耕栽培装置は「ため太郎」2 台と市販プランターにエゕポンプを使用したものの 3 台ですこれを

ホームセンターで買った金属棚の上においてセットしました設置場所にはまったく自然光の入らない

会社の通路です液体肥料としてはハポニカを使用

さて植物が光合成をして成長していくためには赤色と青色の波長の光が必要ですが

これら植物育成ラトは適正な波長の光を放つようにできているので問題はないと思いますが植物が成

長していくためには光合成を行う上である程度の光量が必要でその単位は光量子束密度（μmolm2S)で表

されるそうで育てる植物によって違いがありますが冬野菜なら 110 以上春秋野菜は 160 以上夏野菜

は 250 以上必要とのことです設定した状態で光量子計（藤原製作所 QMSS 型）を使って計ってみると

光源とプランターの間が 20cm と離れていることもありますが植物育成蛍光灯は 144（10cm では 260）

国産 LED フローラは 97（10cm では 160）中国産 LED ゕールユーは 37（10cm で 50）でした蛍光灯

以外は光量不足の感じがしますがレタスの生長にあわせその位置を変えるなどしてできるだけ光量を大

きくして成長過程を観察していきたいと思いますラトはすべて２４時間常時点灯です

レタスは 5 月 28 日に種まきし発芽した 6 月 1 日にプランターに移植しました蛍光灯は購入が少し遅れ

たので 1 週間遅れの６月６日に移植しました次の写真は 6 月 11 日の成長状況です 中国製 LED は赤

色 LED の割合が高いためにかなり赤く写っていますこの時点では赤色 LED の強いプランターL2 の葉

の成長が一番よいようですが根の成長を見ると国産 LED を照射しているプランターL1 のレタスの成長が

一番です

プランターL3 番の蛍光灯は植え付けが 1 週間遅れているので成長もその分遅れております今後 1 週間

単位で葉と根の成長状況を観察してつもりです

６月１４日（第３週目）

L1 は葉も根もしっかり成長しているL2 では葉はよく成長しているが茎も根も今いちの感じこれはや

はり赤色が強いのと光量が少ないことが原因かL3 は１週間遅れているのでまだ成長に遅れがある

６月２０日（第４週目）

L3 ラトのレタスの葉がしおれてきている成長が遅いなと思っていたがラトを近づけすぎていたた

めに熱で周囲が乾燥したのであろう蛍光灯の熱などそれほど感じなかったが幼いレタスにはこたえる

らしいそこで L3 ラトの位置を 30cm ほど上に上げ再度レタスを植えなおすことにしました光量

子計で計ると 100 ほどになっています

L1 のレタスはかなりしっかり育っているがそれでもまだ葉に青さが足りない光量の不足によるものか

と思われるので少し LED を下げてみた光量子の値は 110 になっているL２のレタスは光量の不足か

らか L1 のレタスに比べひ弱な感じがするのでこれも位置を下げたがそれでも光量子量はあまり変わらな

い（37 から 45 に）この状態でもう 1 週間見てみよう

６月２７日（第５週目）

L1 のレタスはまだ黄緑色であるL2 のレタスは元気がないL3 のレタスは少し大きくなってきた

７月４日（第６週目）

先週からあまり成長していない感じがしますやはり L1 のレタスは根もしっかり成長していますが L2

はやはりだめですL3 は熱を持つためか今回もしおれかけています

7 月 12 日(第 7 週目）

太陽光の元であれば十分に育って今頃食べ時になっているのだが結論から言うとやはり光量不足で成長

不全というところですL3 については今回も苗がかれてしまったがこれにはおそらく育てている私に何

らかの落ち度があるためと思えます

今回の実験はこの状態でひとまず中止し来週から改めて栽培しなおしてみようと思います

7 月 18 日(第 8 週）

本来ならば約 50 日たつので食用に供することができるくらいに成長していてもいいのですがやはり光量

の不足のためかあるいは肥料不足のためか発育不全の状態で終わってしまいました何分にも初めてだ

ったので育て方に問題があったのかもしれないひとまずレタスを取り出して写真に取りました

LED 野菜工場 夢の扉

異常気象が叫ばれるなか農作物の不作豊作は天候が影響しますTBS「夢の扉」では天候に影響しない農業の革

命ともいえる近未来の野菜工場として LED 照明だけによる野菜工場が紹介されました

LED 照明の野菜工場

この LED 照明による野菜を育てる植物工場の実験施設を作ったのが玉川大学農学部の渡辺博之教授です２０１

０年に完成したこの工場外の天候に一切関係なく野菜を育てることができるといいます

LED の光の色で野菜の性質がまったく変わるといいますたとえばレタスを赤い光で栽培した場合光合成が促

進され２４時間光を当てるので通常２ヶ月半～３ヶ月かかるレタスがなんと２週間で収穫できるといいますそし

て味も赤い光でそだてると甘くなり通常のレタスの５倍の糖質になるそうですまたビタミン A も通常の 13～14

倍高まるそうです青い光で育てたレタスは葉の色は褐色化し味も苦味が出てきますこれはポリフェノール

の一種であるゕントシゕンが増えたことによるものだそうですなぜ増えたかはまだ解明されてませんがポリフェ

ノールは高血圧コレステロール対策に有効だといわれますこれは光によって目的に合わせた野菜を育てることが

できることになるといいます野菜の種類はレタスの他にシソも栽培中

この野菜工場成長の早さや栄養成分が増えることだけがメリットではありません

それは安全性です雑菌や害虫の繁殖を防ぐため土を使わない水耕栽培で育ています必要な栄養は自動で水に添加

させており農薬が使う必要がない安全な完全無農薬野菜だということです

価格も今の市場価格と同じくらいで出荷できると考えているそうです

またここで使用されている LED は渡辺教授が開発したもので水で冷やすことにより 20 年間ハパワーで 24 時

間点灯し続けても光量が落ちないそうです

野菜工場で LED チゴ栽培

食糧危機で主食となるモなどの根菜類や穀物ですがこの LED 野菜工場ではその栽培に成功していませんつ

まり実のなる野菜はまだ成功していません

そこでチゴの栽培に挑戦しますもし成功すれば穀物などへの栽培の足がかりになると考えられます

実をみのらせるには従来の光よりさらに強い光が必要だとうことでこれまでも５倍のパワーをもつ新型 LED で

挑戦します様々な色を組み合わせて行なった結果試行錯誤の末ようやく実をつけることに成功その味も思った

以上に甘かったそうですこれによりモなどの根菜類や穀物の栽培の道が開けてきたということです

この野菜工場協力企業による移動可能なコンテナ型野菜工場もすでに開発されこのシステムで世界の食糧危機を

救おうとしてます早く新鮮な野菜の供給に困っている国に使ってもらうことが目標だといいます

LED 照明を見た感じはちょっと引いてしまいそうな色ですが様々な野菜が作られる日もそう遠くない感じですね

今後の野菜工場にますます期待したいですね