MeshPL
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Growing plants under LEDs
Hello everyone!
I'll be attempting to grow plants under LEDs (probably). I'll try tomatoes, I think. Do you think 80 typical 3mm LEDs would do for 5 plants up to 1
month? I will restrict sunlight from going in, so LEDs will be the only source. However I'll put aluminium foil around to prevent light from being
wasted.
I'll try different colors of LEDs for sure. I think that I'll use 80 red LEDs and accordingly less of others, so that wattages of all sets are the
same. (3 red LEDs have similar power to 2 blue). Or I'll try so-called "power LEDs" of total power equal about 8W.
Well, I know this is borderline topic for this forum, but well "Experimental biochemistry and biology, biosynthesis, and natural products." includes
biology and that is thing I'll be doing. If this is too off-topic, I'm ok with topic being deleted.
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Harristotle
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LEDs and plants
Hi MeshPL,
wavelength of the light is important.
Plants need two wavelengths of light: one is 680nm and lower and the other peaks at 700nm.
It is therefore important to use the correctly balanced light.
LEDS have fairly narrow wavelengths of light: it is important to get one that is suitable for plant growth.
Ebay sell 3 watt leds that are supposed to be good for them - the violets that I grew in tissue culture (6 watt system) were not impressed and did
much better in filtered sunlight. Whether that is an intensity or a wavelength issue, I don't know.
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hyfalcon
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you need 35-50 watts per square foot for fruit or flower production in plants.
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hissingnoise
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| Quote: | | I'll try different colors of LEDs for sure. |
Green leaves, of course, have no use for that particular colour ─ so they do well in a balanced mixture of red and blue . . .
Lighting discussion here!
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MeshPL
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Ok. Thanks!
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Fulmen
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That would depend on the type of light you use and it's color spectrum. You can dump 10 times that in the wrong region and not get anything. IIRC
that number is based on HPS or metal halide, right?
We're not banging rocks together here. We know how to put a man back together.
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hyfalcon
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That would be correct. LED's can be set up to be more efficient, but the cost is still above and beyond traditional HPS lighting.
Of course if you just like to tinker....
http://www.rollitup.org/t/diy-led-grow-lights-with-cree-cxa3...
[Edited on 5-3-2016 by hyfalcon]
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wg48
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Your problem will be trying to get data on the actual light output of the LED and then interpreting it. Its a mine field of bald numbers and undefined
or poorly defined units.
Consider your suggested 3w LEDs are they old ones with low effiency or more modern ones with higher effiency. What is the light output.
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Fulmen
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WG48: You're right, the biggest problem will be finding useful data. Most sources uses lumens, but that is weighted against human eye sensitivity and
not photosynthesis.
We're not banging rocks together here. We know how to put a man back together.
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aga
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Sunlight is generally available and cheaper ?
The question fits fine in the topic iMHO.
My limited experiments with plants have been with Sunlight and varying the nutrients and growth media.
It is fascinating how germination (for example) is affected by temperature and moisture.
Look up 'Seed Germination, Theory and Practice' Norman C Deno, Professor Emeritus of Chemistry.
He went on from Chemistry and did Biology with definitive results, as evidenced in his paper(s), such as that above.
[Edited on 5-3-2016 by aga]
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MeshPL
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Well, growing plants under sunlight is nothing new.
I don't think I'll use any special light colour, but I've decided to use "power LEDs", 10 times 1W per each 5 plants. LEDs are quite efficient, so
this corresponds to at least 40W of incandescent light bulb.
I don't think I'll use any special varieties, just few basic colours and maybe 2 combinations.
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Tsjerk
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Nice review, not the newest, but certainly a good read to understand the basics.
http://hortsci.ashspublications.org/content/43/7/1951.full
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careysub
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This is very thoroughly explored topic at this point.
Plants use a very wide range of light for photosynthesis. If you look at a chart of the measured quantum efficiency of photosynthesis with wavelength
(simple absorption charts aren't particularly informative), see attached, you see that the plant response actually peaks in the red band around 600
nM, so this is where light is most efficiently employed. There are also very efficient LEDs available in this band.
So why use any blue at all?
Photosynthetic efficiency is not the whole story. Some blue spectrum light is necessary for most plants to promote normal growth patterns, it appears
to have some regulatory effect.
LED grow-lights typically have 3 red LEDs for each blue LED, producing a pinkish light. Inexpensive LED "flying saucer" grow lights with a balanced
combination of LEDs are cheaply available on eBay.
[Edited on 6-3-2016 by careysub]
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careysub
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Quote: Originally posted by Fulmen  | ...
That would depend on the type of light you use and it's color spectrum. You can dump 10 times that in the wrong region and not get anything...
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Photosynthesis is a lot more versatile than that (see my quantum efficiency chart above).
Over nearly the entire visible spectrum of light the quantum efficiency of photosynthesis never drops by more than 30% - only at the very lower limit
of human vision (deep, deep red, where the human eye is also very insensitive to light) does it drop as low as 50%.
People commonly think that plants can't use green light, since plants appear green (indicating green light is reflected), but this is more illusion
that anything. The human eye is maximally sensitive to green light, and so tends to over emphasize green in the reflected spectrum; then too, plants
aren't really very green, compared to something that really is highly reflective in green (like a synthetic pigment). Put a bright green color card
next to most any plant and it will look pretty drab. Photosynthesis is actually 80% relative efficient in the middle of the green band.
[Edited on 6-3-2016 by careysub]
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MeshPL
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Wow, that efficiency vs. wavelength chart seems great (again, WOW), wherever you got it from.
[Edited on 7-3-2016 by MeshPL]
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careysub
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Query Google Images with "photosynthesis quantum efficiency". The chart is from :
http://biology.mcgill.ca/Phytotron/LightWkshp1994/Contents.h...
http://biology.mcgill.ca/Phytotron/LightWkshp1994/1.5%20Bugb...
NASA-CP-95-3309
"International Lighting in Controlled Environments Workshop"
The original chart was published in:
McCree, K.J. 1972. The action spectrum, absorbance and quantum yield of photosynthesis in crop plants. Agric. Meteorol. 9:191-216
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MeshPL
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I said tomatoes? I may need to swithch to radishes. They grow easily and fast (you may get a crop within 1 month). And are smaller. Not very
nutritious though. Due to different circumstances I will not be able to look after those plants for so long without few day breaks.
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crazyboy
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Tsjerk is the only person here making any sense, the paper he linked definitively debunks most of the speculation going on in this thread. Plants are
complex organisms. The wavelength of light does more than simply drive photosynthesis, it provides cues for stomatal control and phototropism.
You can't just use 680nm and 700nm because those happen to be the wavelengths of maximum absorption for the two photosystems. Read the review Tsjerk
posted, red light alone does not do well. Supplementation of blue and green light is very beneficial.
I don't have any experience in this matter although I find it interesting, personally I use daylight CFLs for growing plants. If you want to build
your own I would recommend a ratio approximately 2:1:1 Red:Green:Blue as a place to start. As for power, most scientific papers use umol/m^2/s^2 for
practical use I think watts/m^2 is more logical. I would look at commercial units and see what wattage they use and for how big an area they are
recommended.
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MeshPL
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umol/m^2/s^2 seems to be a sound sounding unit, but once you realize, that a mole of blue light and a mole of red light are not equivalent, and no one
actually cares about the amount of photons produced, only power required to produce that light.
However, if the wavelength of said light is fixed, that unit is much more sensible.
Also, I think that swithching to radishes is a good idea, because they should grow with less light better than tomatoes and are smaller, what means
that keeping constant LED wattage, I can get more umol/m^2/s^2 or W/m^2 or luxes.
One of the most anoying thing about researching this topic, is the fact that most of the data is about cannabis, because pot-growers are the ones
usually interested in growing plants in LED light. However cannabis requires quite a lot of light, while radishes may grow with much less light
(speaking of both duration and intensity)
Another quite interesting site: http://www.ext.colostate.edu/mg/Gardennotes/142.html
[Edited on 16-3-2016 by MeshPL]
[Edited on 16-3-2016 by MeshPL]
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Tsjerk
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You should be happy with the pot-heads posting their experiences in an amateur setting. Once you get the hang of quickly recognizing BS you can get a
lot of info out of those discussions. Combine that with what you read in literature. If you don't like the pot-heads you should stick with literature,
a good starting point is ncbi.nlm.nih.gov from an university library or over an university vpn (maybe you can use the login from a friend or family
member.
Cannabis is not a bad starting point for information. Try to find out whether cannabis is a so-called "light" or "dark" species ( I forgot what is
what again). One of the two responds to darkness in its hormonal householding, the other one to light. Better said; they respond to either the
prescence or absence of light. When your species falls in the same catagory as cannabis you are save in assuming your plant sort of behaves the same
in a similar light regime (at least save enough in case you can't find specific info on your species).
Whether radish needs more or less light is less important then the light regime and light wavelenghts it needs. The amount of light you can always
bring down by using less LEDs or hang them higher and put more plants under.
If you can't find the light dark thing; cannabis starts flowering upon shorter days, and flowering will be severly effected by minute amounts of
specific wavelenghts during the "night" (red iirc). From this information you can extrapolate the answer. For radish; if you can't find a direct
answer you can often extrapolate it from the natural life cycle, taking in account things like wheter it is a one year or multiple year plant and in
what time of year it flowers (if it flowers), my first guess is that it falls in the same group as cannabis
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chemrox
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For tomatoes I would use exactly the same lights you would use for growing cannabis as per the link posted by hissingnoise.
"When you let the dumbasses vote you end up with populism followed by autocracy and getting back is a bitch." Plato (sort of)
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careysub
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Here is a good article on day-length (actually night-length) sensitivity for vegetables:
http://ext100.wsu.edu/skagit/wp-content/uploads/sites/5/2014...
Cannabis is night-length sensitive, it starts flowering when exposed to about 11 hours of darkness each day.
Foliage producing plants (lettuce, etc.) require less light than fruiting plants, or plants that produce starchy tubers.
Indoor lighting is much less intense than daylight so over-lighting is never a problem, though under-lighting can be.
Cannabis plants are fairly typical plants in their requirements so anything that works with them, fertilization, light intensity, etc. will work well
for most other plants.
Attachment: 042712.pdf (32kB)
This file has been downloaded 650 times
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MeshPL
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Radishes are long-day plants. However this doesn't mean you want to supply them with too much light. If you do, they will like it so much that they
will reward you with flowers, not bulbs. Reportedly some radishes plantted in June or July fail due to long days (and high temperature).
For radishes:
-cold/short day length->bulbs
-hot/long day length->flowers and seeds (that's what you don't want)
Note that day length and light intensity are not the same! Because I will be using rather crude approach (no specialised LED wavelengths, no elaborate
LED combinations), I will not use any elaborate light regulation, and will setup a timer synced with sunrises and sunsets, so that radishes in control
group, grown in the sun (but still indoors, next to a BIG window on a southern side of the house) experience the same "day length".
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