Make:

Plants need UV for photosynthesis, and I rather doubt that LED xmas lights give off significant amounts of UV. More likely the sprouts are just sprouting the way they would in darkness.

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I'm skeptical, too, but apparently NASA has been researching LED light and plant growth.

http://tinyurl.com/1vv

I'll be keeping an eye on the veggie blog for updates on legginess. :)

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Posted by: The Cheap Vegetable Gardener on January 14, 2009 at 10:52 AM

Actually most UV spectrum light can actually harmful or at best neutral to plants.

Tell you the truth I was also skeptical as well which is the reason I made the $3 investment to do the experiment versus spending $100-$500 on commercial LED grow lights. I must say I have been impressed so far, I doubled the lights by adding some red LEDs (need to write-up another update) and results have been great. Plants (cucumbers/onions/flowers) are staying stalky with dark green leaves quickly outgrowing their current home and requiring me to move them to the computerized automated grow box.

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Oh, cool, thanks for the update! :)

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@ cheap vegetable gardener-

cukes? onions? flowers? suuurrree....

I've only ever heard of 'grow boxes', automated or otherwise, being used for one specific herb.

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wonder how closely the spectrum matches real light?
also we can get 20 lights say for $4 but this looks like hundreds ....? could add up!

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bob, I think they got strings of Christmas lights right after Christmas, so they were really cheap.

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Would a Red Gel Filter over the LED help with the spectrum?
I have been wondering about this for days.....

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Posted by: The Cheap Vegetable Gardener on January 14, 2009 at 3:04 PM

@bob
I picked this up for $3 a string after Christmas. Should have bought more given my current results.

@Hmmm
I am curious about filters not sure if the loss of intensity will supersede the better spectrum

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Chlorophyl A absorbs light at violet/blue and red/orange wavelengths (which is why most leaves look green). UV is not needed.

An LED has a very narrow spectrum. Placing a green filter over a red LED will result in almost zero light transmission because the red LED makes almost no green light.

This is an interesting idea, but I don't think xmas lights will produce nearly enough light. You could do much better by buying some ultrahigh brightness LEDs in bulk on ebay and wiring them into the lid.

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This experiment really needs a control group I think.

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There are cheap UV leds around, the same used to scan paper money and produce wood lamps-like light effects. Would adding some of those leds help?
It would be also interesting to know if cold white leds are better than warm white ones for this job, cold white ones are usually cheaper because their emission is less attractive to us.

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Can people please do their research before writing on websites stating their un-educated opinion.

UV is not good for plant growth. however, during flowering, is does theoretically increase the trichome production on cannabis plants as the resin actually protects the flowers from UV. the idea is that giving the plant UV stimulates this defense mechanism.

And thanks TD, at least someone has some clue. Any filter will only reduce the light output and be a bit useless. If you want to know how close led light is to natural light, not at all, has no resemblance at all. LED light is very specific output in color, even if you mix red, green, blue to produce what appears to be white light, the actual wavelength produced is very different.

Chlorophyll (the stuff that reacts to sunlight) reacts to blue and red light. but it's not just red and blue you need. it is quite specific bands. Chlorophyll-A absorption exists at light wavelength 410nm-ish and a peak at 430nm (blue)and then another peak at 660nm (deep red). Chlorophyll-B has a peak absorption band at 453mn and another peak at 642nm. This is a little unfortunate as light emitted by the GaN-based (blue) LED peak at about 465nm with only a small portion being emitted at 453 and very little at 430nm and practically nothing at 410nm. Light from InGaAlP/GaP (red) LED's peak at 630nm. similarly only a small amount is in the 645nm range and practically nothing at the 660nm range.

So standard LED's are not as efficient as one would initially think. You can get LED's in 660mn, 630nm, 450nm, 430nm and even 410nm. however they can get extremely expensive. e.g. 410nm LED's can be found as high as ~$100 per 10w high power LED and I can't find them cheaper then a a few dollars each for 5mm ones.

LED's do work, but you have to do it properly. going cheap
xmas lights is not the solution.

:o) Phil

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