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BY THEO TEKSTRA – MARKETING MANAGER, GAVITA INTERNATIONAL BV
PART
6
Is this the new step
in plant lighting?
A WHITE
REVOLUTIONGa
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In the series “Light Matters,” Theo Tekstra discusses the different aspects to lighting, such
as quantity, quality, efficacy, special applications, new developments, and the science behind
it. In Part VI, Theo explains the applications of the Ceramic Metal Halide.
Image 1:
Philips CDM Elite Agro lamp
dated March 2012
LIGHT MATTERS
Why Evolve from MHMetal Halide (MH) lamps have always been popular in the
grow light industry because of their wide spectrum, including
much more blue light than HPS lamps. Instead of sodium,
MH lamps contain, as the name implies, metal halides, or
metal salts. When excited in a plasma these components
start emitting a bright light. The spectrum depends on the
composition of the salts.
To understand why CMH lamps are a step forward we need
to know a few distinct disadvantages of MH first:
1. Efficacy
Though they look quite bright to us, in terms of plant
light (PAR) MH lamps are not so efficient. Think 25-
40% less efficient than HPS.
2. Color stability
MH lamps shift in colour during their lifetime.
3. Light maintenance
MH lamps lose up to 20% over the first 2000 hours
and an average loss of more than 8% per 1000 hours
over their lifetime is no exception. Compare this to
high-quality DE HPS lights which lose less than 3% per
5000 hours of operation.
4. UV emittance
They emit a lot of UltraViolet radiation, including
UVC. According to the FDA’s latest report, “UV
Burns From MH Lighting Remains a Public Health
Concern,” one broken bulb can emit an entire day’s
exposure to the sun in just eight minutes. In most
cases, regulations require MH lamps to be used
behind a glass filter, to filter out the UV radiation but
also for safety. See point 5.
What’s in a NameCMH stands for Ceramic Metal Halide, a relatively
new type of High-Intensity Discharge (HID) lamp, like HPS
and Metal Halide. It’s a little bit of both, but we will touch
on this later. Developed in the early 80’s, Philips made it
a commercially successful product in the 90’s, when it
launched a line of CMH lamps under their product family
name “CDM.” So, that’s the first ”alternative name” you will
see pop-up.
Sunlight Supply, a hydroponics supplier and lighting
manufacturer, introduced a fixture with that lamp,
registering the trade name “LEC” - Light Emitting Ceramic.
It has a very similar structure as LED (Light Emitting Diode)
and LEP (Light Emitting Plasma), and it aims to compete
with these. The only flaw in the name is that the ceramic
material doesn’t actually emit any light, but that’s a detail.
So, there is the second brand name of CMH.
I’m sure you have heard about a new type of lamp that is creating waves in the grow community:
CMH, CDM or LEC!!?? So what is this and how relevant is it? Is this the new step in plant
lighting? Where did it originate from and what are the benefits?
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Image: high-speed camera image of an exploding MH lamp
(source: YouTube)
Image: ceramic arc tube (GE CMH 250 lamp)
LIGHT MATTERS
57
Images: /O versus /E MH lamps (source: Venture Lighting)
- A rupture of the outer glass balloon will not automatically
extinguish the lamp. As the glass balloon is responsible for
filtering out all dangerous UV light, a dangerous situation
will result. Accidents causing broken outer balloons in
public spaces, such as stadiums and large halls, have caused
regulations to become more strict. Lamps suitable for open
fixtures, therefore, have protection to prevent this from
happening, usually through a double glass balloon.
So, What is Ceramic Metal Halide?The only real difference between MH and CMH is the
C which stands for “Ceramic.” It refers to the arc tube
material used in a CMH lamp, which is a ceramic material,
polycrystalline alumina, the same material used for HPS
lamps. More stable than quartz glass (resistive to the
aggressive salts), it can withstand much higher temperatures,
ones at which quartz glass would almost start to melt. By
using a higher temperature inside the arc tube the efficiency,
colour stability, and light maintenance can be greatly
improved. I do say “can,” because not all CMH are much
more efficient or have a much better light maintenance.
5. Not always suitable for open fixture
Most MH lamps are not suitable for installation in a
fixture without a glass filter. There are two reasons
for this - UV emittance, as seen in point 4, and the
behaviour of the arc tube, if it fails, is a safety issue.
Over time the quartz glass arc tube of an MH lamp
corrodes from the extremely aggressive MH salts
inside the lamp, and cause discoloration of the arc
tube, diminishing the output. In some cases, ignition of
a warm lamp or a deteriorated arc tube can lead to an
explosion of the arc tube. The pressure inside an MH
lamp is much higher than the pressure inside an HPS
lamp and the temperature inside can reach over 6000°
Kelvin. An explosion creating super hot particles can
even be a cause of fire.
6. There are few MH lamps suitable for
open fixtures, ones that have special preventive
measures to contain an arc tube explosion, such as a
double outer jacket or an extra glass shroud around
the arc tube, are suitable for open reflector. Look for
the ANSI designation /O (suitable for open fixtures).
The National Electrical Code (NEC) and UL prohibit
other MH lamps to be used in open fixtures - you
are in violation of the installation code if you do so,
and damages as a result of such an installation are not
covered by your insurance.
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Image: CDM Elite 315 lamp for open fixtures
Image: CDM Elite 315 lamp for closed fixtures –
no extra outer balloon
CMD Elite 930
CMD Elite Agro
CMD Elite 942
59
LIGHT MATTERS
Image: MasterColor Ceramic Metal Halide HPS-Retro White
Renewed InterestThe CMH lamp that created all this new interest is the
CDM 315 lamp from Philips, in particular, the CDM Elite 315
Agro. The CDM 315 already was around for a while when
Philips created a new spectrum, adding more red light than
the standard 3000 Kelvin lamp, producing a sort of purple
glow. It also added efficiency, reaching 1.9 µmol s-1 per Watt
initially with a light maintenance of about 94% per 5000
hours. There are two more versions of this lamp, developed
and suitable for general lighting: The regular 942, with a
4200K colour temperature, and the 930 at 3000K, but at a
lower efficiency in the PAR spectrum. Make sure you get the
special Agro lamp if it is efficiency you want
The standard CDM lamps are also available in versions for
a closed fixture. Remember, these are NOT to be used in
open reflectors:
It was only in the early 2000s that manufacturers were able
to produce a lamp with a higher wattage than 150W. The first
commercial “medium wattage” lamps (250W and 400W),
were launched by Philips under the brand MasterColor
Ceramic Metal Halide HPS-Retro White. They were meant to
replace 400W HPS lamps in magnetic low-frequency ballasts in
general lighting, and provide a much better quality light. Hence
the HPS-Retro (HPS retrofit). The wire around the ceramic
arc tube was to prevent fatal explosions, and so it passed the
/O certification for open fixtures. With the introduction of
the new generation, these versions have been phased out.
A Closer Look at SpectrumNote the difference in the red spectrum between the 930
and the Agro:
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Image: Chinese CMH 315 lamp
61
LIGHT MATTERS
The CDM Elite 315 Agro is the most suitable for plant production, as it produces the most photons in the PAR spectrum. However, if you are looking for the best colour reproduction and most sun-like spectrum, the 942 would be the best choice.
Limitations• These lamps require a specific low-frequency ballast.
Most are around 200 Hz and provide the lamp with a square wave output. The ballasts have a warm restart protection, which automatically times out re-ignition for about 10 minutes.
• The lamp holders only receive the /O type CDM lamps. • The output power of 315W. There are higher wattage
CDM lamps available, but these have not been optimised for plant growth, are not as efficient, nor do they provide the same light maintenance. Perfect for general lighting, not for plant lighting. The 315W being the only real available option means that in order to get the same output as a 1000W DE HPS running at 100%, you need 3.5 – 4 CDM fixtures. This translates into a higher overall investment and more maintenance. The CDM lamps are slightly less efficient than DE HPS (1.9 µmol s-1 per Watt versus 2.1 µmol s-1 per Watt) and have a lower light maintenance (3-4% less light maintenance per year), so the average light output is actually a little bit lower.
The spectrum of the CDM, however, is superior over the HPS lamp: It contains much more blue than the HPS lamp. By no means does the CDM 315 Agro mimic the sun, but you can expect a healthier plant. Most advantages will be seen in the morphogenesis of the plant and the production of terpenes and essential oils. To really make a difference in that latter department though you will need to start adding UV light in safe dosages. It will not, however, result in an extra-spectacular yield.
So Where Would I Use the CDM 315 Lamp?A big advantage of a lower wattage is that you can come closer to the crop. Using more, low wattage lights instead of one large fixture, will give you a better light uniformity and horizontal penetration of the crop. If you have a small room, and the money to invest in more fixtures, a few CDM 315W lamps really do an outstanding job. In vegetative rooms where you need less intensity, and more blue light is an advantage, CDMs can also be a solution. Do remember that in a large room, the initial investment can be quite high.
China! China!Of course, there are other CMH lamps out there, many coming from China. There is one manufacturer who makes a decent lamp with a good spectrum, but with a lower efficiency (10% less light – 1.7 µmol s-1 per Watt!) and a
Retrofit WarningThere are many (Chinese) double ended MH lamps sold on the market today for use in open, double ended fixtures. A REALLY bad plan, for many reasons:• These lamps do not have a /O rating (with one exception, which
uses an extra glass cylinder around the lamp).• Many discharge very high UV levels, making it dangerous to work
under without proper protection. One manufacturer proudly announced that they emitted “the good UV – UVC.”
• Most double ended fixtures have specifically been developed to drive HPS lamps, which do NOT need a warm re-start protection. Running MH lamps on these ballasts is dangerous, as re-starting a warm MH lamp can lead to an explosive failure of the lamp. We have been able to replicate this in our labs. Do NOT try this at home, boys and girls!
• You will lose the warranty on your ballast if it has been specifically designed for HPS lamps. 3
lower light maintenance. You can recognise it by the arc tube shape, which is less round than the original. Most of the private label CDM lamps all come from that same factory.
To counter the lower wattage limitation, there are even double ended lamps which contain 2 or 3 CMH arc tubes in series. This is not a good plan, as it can lead to ignition failures and premature failures of one of the arc tubes. Also, remember that MH and CMH lamps need to have a double jacket to be suitable for use in an open reflector, and use a LOW-frequency ballast with a time-out for re-igniting warm lamps. They are NOT suitable for a retrofit to a high-frequency HPS lamp!
So, there you have it: A primer in CDM and the application of it. A great lamp, with some limitations. Is it a full HPS replacement? For small grows it can be, due to the high investment costs compared to HPS. Does it replace full spectrum plasma lights? Though it is more efficient, the spectrum is still a bit too peaky to mimic sunlight, and the lamp lacks UVA and UVB. CDM is an expensive lamp to replace every year, but for a small cash crop that should not be a limitation.
Gard
enCu
ltureMagazine.com
US 15