What is the upper limit on the light intensity for growing plants indoor in a hydroponic system? Except my electricity bill off course :-) e.g. Are 1000W HPS light per sq.m. ok, as long you can keep the heat under control? Or what happens when I add too much lighting?

I'm trying to grow thai basil (horapa and krapao), bird eye chili's and thai eggplants at a high as possible efficiency because we use them at our restaurant.

  • @Ecnerwal I was looking at the "Lampada Professionale Gavita PRO 1000 DE" at 138000lumen it seems very powerful... however 500 euros, yaiks that is a steep price for growing basil and such – Den Uil Oct 5 '15 at 11:25
  • ...exactly. Both the setup and running costs tend to favor shipping the plant products in most cases, unless there are very special circumstances. Lumens are human-eye-response weighted and favor yellow-green since the human eye is most sensitive there. Plants use light differently and tend to favor red and blue. I guess if nobody else has come up with a better one I'll take @GardenerJ 's advice and put the other comment into an answer. – Ecnerwal Oct 5 '15 at 11:45
  • Photosynthetically active radiation (PAR) is the number you want to use: en.wikipedia.org/wiki/Photosynthetically_active_radiation Get it too high and all your thylakoids en.wikipedia.org/wiki/Thylakoid will become unstacked, and your plant will start to suffer radiative damage. Maximum tolerance likely depends strongly on plant type. – Wayfaring Stranger Oct 6 '15 at 19:24

"As high as possible efficiency" in terms of ...what, exactly? Sure isn't going to be electrical cost if you are dumping in enough heat that you need artificial cooling as well as the power for the lights. Supplemental lighting in a greenhouse at least has the potential to make use of some of that heat in a positive way, but heating the greenhouse overnight is often enough of a fiscal drain to make the plant products excessively expensive anyway (depending on the exterior climate, of course - in milder "but still too cold for basil" climates less supplemental heat is required than where I'm at and base my greenhouse cost assumptions on.)

Mean midday solar radiation in Thailand in Springtime averages 800W/sq m and HPS lights are far from 100% efficient at converting electricity into light, so you ought to be safe if you can dispose of the heat. 800 "PAR Watts" (photosynthetically active radiation) per square meter should be "safe" if you can control the temperature, but might take 2500 watts of electrical input for HPS lights (and getting rid of 1700 watts of heat) based on some quick and shoddy research. MH might get you down under 2300 watts input for the same light to plants. But see below...

Revising (slightly) the shoddiness level of the (still pretty shoddy) research, perhaps a factor of 0.368 should be applied to the solar irradiance to get it's PAR fraction, leaving 295 PAR watts/sq m and revising the equivalent MH wattage down to ~850 and HPS to 950-ish.

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