Why is light important?Why is light important?

1.) Photosynthesis

6CO2 + 12H2O ((chl chl && light light) )

C6H12O6 + 6O2 + 6H2O

2.) Needed for chlorophyll

production

3.) Photomorphogenesis - development of certain plant parts, esp. flower initiation and development, seed germ...

Why is light important?Why is light important?

4.) AnthocyaninAnthocyanin production

5.) Light is energy! Some is converted to heat when it strikes a plant surface

6.) Light influences translocation in the plant

7.) Light can affect abscission (dropping of plant parts) when intensity suddenly changes

LightLight inintetensnsityity

-Refers to brightness

-Often the limiting factor for growing or maintaining plants indoors

Light measurementLight measurement

Light can be measured

in many ways!

- Light meter (photoelectric cell)

FootcandleFootcandle = the unit of illumination equivalent to that produced by a standard candle at a distance of 1 foot

LuxLux = the unit of illumination equivalent to that produced by a standard candle at a distance of 1 meter

ConversionConversion:

1 fc = 11.1 lux1 fc = 11.1 luxThese units measure only visible light

(what the eye can see!)

For scientific reporting of light quantitylight quantity, you might hear the following terms:

candela

lumen

photon flux

quanta

joules

1.) Natural Natural (sunlight)

2.) ArtificialArtificial (bulbs and tubes)

3.) Combination of the above

Sources of light for an interiorSources of light for an interior

SunlightSunlightFactors affecting light penetration into a

room:

1.) WindowsWindows

-type (glass/plastic/glazing)

-reflection

-barriers (overhangs, screens, curtains, shades, buildings and plants outside, dirt, etc...)

-orientation (N, S, E, W)

SunlightSunlight2.) Latitude

(distance away from the equator)

J F M A M J J A S O N D JJ F M A M J J A S O N D J(calendar year)(calendar year)

2424

22

4466

8810101212

14141616181820202222

BurlingtonBurlington

AtlantaAtlanta

EquatorEquator

SunlightSunlight

3.) Geographic region

-annual cloud cover

-atmospheric pollution

-humidity

-elevation

Artificial lightArtificial light

Supplemental to sunlight

-extend hours of light

-increase inintentensitysity of light

Sole source

-role: room lighting

plant lighting

combination

Considerations not necessary with sunlight:

spectral emission = range of colors produced by the light

Light Quality!!!

Artificial lightArtificial light

380 430 470 500 560 600 650 760

oorraannggee

vviioolleett

bblluuee

ggrreeeenn

yyeellllooww

rreedd

iinnddeeggoo

Visible LightVisible Light(nanometers)(nanometers)

Gammarays

X-raysUltra-violet Infrared Radio

PPhotosynthetically AActive RRadiation (PPAARR))

Range =

400400 - - 700700 nanometers

Based on length of each wavelength of light

~~~~~~~~~~~~~~~~~~~~

ChlorophyllChlorophyll and associated pigments utilize light energy primarily in the blueblue (430 430 nm) and red red (670670 nm)

Choosing artificial lightsChoosing artificial lightsSources:

Incandescent bulb

ProsPros:

--small

--no special fixtures

--dramatic

--range of wattages available

ConsCons:

--light is concentrated

--7% of energy usable light

--90% of energy heat!

--short life (750 hrs.)

--high in redred//orangeorange & low blue blue

Fluorescent tubes(cool-white, warm-white, daylight)

ProsPros:--diffuse light, new fixtures avail.--efficient! (7x incandescent!)--22% of energy usable light--cool! 36% of energy heat--last 8,000 - 9,000 hrs (15x longer than incandescent!)

ConsCons:--work best if 70 - 90oF- - traditionaltraditional fixtures bulky --low far-red emission--contain mercury--emit ultraviolet lightemit ultraviolet light

Cool Cool whitewhite

WarmWarmwhitewhite

Daylight fluorescent vs.

Incandescent bulb

400400 500500 600 600 700 700

100908070605040302010

0

FluorescentFluorescent

IncandescentIncandescent

Rel

ativ

e en

ergy

Rel

ativ

e en

ergy

(nanometers)

Sodium vapor lamps(HID lighting)

ProsPros:

-25-35 % of energy visible light

ConsCons:

-yellow/orange/red spectral emission only!

-large ballast (requires special lighting fixtures)

What happens when light contacts a leaf?

ReflectedReflected

Transmitted

Absorbed

Ways to increase Ways to increase artificial light:artificial light:

• Added white reflectors to fluorescent fixtures

• Paint surrounding walls white

• Regularly clean tubes to remove dust

• Regularly clean plants to remove dust

• Change tubes regularly

• Keep plants centered under fluorescent tubes

Natural vs. Artificiallight intensities

• Noon sun during summer can measure 10,00010,000 fc

• Cloudy winter day: 500-2,000 fc

• Inside rarely exceeds 1,3001,300 fc– typical office 20-30 fc

– typical living room • day: 10-1,000 fc• night: 5-10 fc

Minimum light required for plant maintainance???

100 fc100 fc

-Light quantity--Light quantity-Total light per day = footcandles of light x hours of light/day

Example:

100 fc x 16 hrs of light/day

1,600 fc hours/day

Sometimes, extending the daylength can compensate for a lower light intensity...