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There are many lighting products with different rated power. What is the typical grow light intensity (power per unit area) for edible greens?

Sparkler
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  • http://gardening.stackexchange.com/questions/5271/how-much-lighting-do-i-need-for-growing-lettuce-using-indoor-hydroponics – Graham Chiu May 28 '16 at 04:01

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Full sun conditions are about 100,000 lumens per square meter. LED and fluorescent lamps produce about 60 lumens per watt which would mean 'burning' about 1.7 kW of electricity per square meter - a fairly astounding number.

However, probably something like 20,000 lumens per square meter would be adequate if the light was tuned to only produce wavelengths adsorbed by chlorophyl - there are 'grow lamps' that are tuned just this way. So, you will need about 350 watts per square meter with LED or fluorescent lamps, maybe a bit more.

  • tuning for chlorophyll: isn't it just visible light? – Sparkler May 28 '16 at 19:16
  • No, not all visible light. Leaves look green because green light is reflected. Shine a red light on them and they will look black because red light is adsorbed. Though there is a bit more to it, grow lights are tuned to produce light primarily at the wavelength's adsorbed by chlorophylls - different than the spectrum produced by incandescent bulbs and others that we use for interior lighting. The sun, on the other hand, produces ali wavelength's. –  May 28 '16 at 20:24
  • So I should just get LEDs that emit 650nm and 450nm..? http://hyperphysics.phy-astr.gsu.edu/hbase/biology/ligabs.html – Sparkler May 28 '16 at 20:49
  • Yes, but commercial enterprises have already done this for you - look on-line or visit your local hydroponics store. I apologize for the confusion, I was only trying to explain why 20% of the light produced by the sun might be enough with the right color of light. –  May 28 '16 at 21:04