different shades of red.

From: Anders Espefält <anders.espefalt.4783 at student.uu.se> on 2004.08.18 at 09:42:10(12018) Hi! Since there has been a number of postings on lights I would like to make a remark. Its taken from "Biology of Plants" fifth edition by Raven, Evert and Eichhorn +More page 581-583 .Etiolation i controlled by phytochromes. The plant measures the ration between 660nm and 730nm (different shades of red light) vegetation absorbs and reflects almost all light below 700nm. Therefore the amount of 730nm is much higher than 660 and the plat "feels" shaded and begins to grow tall and thin and yellow (etiolated). Lightbulbs radiate much light in the longer wavelengths, such as very much infra red (heat radiation). And also sends out more 730nm than 660nm and plants under only lightbulbs feel shaded. Blue light is not involved in this adaptation. page 574 But blue light (400-500nm) is the light that mediates phototropism (ie the mechanism that makes the plant orients towards the light). page 619-620: Blue light have long been shown to stimulate stomatal opening in some plants independently of CO2. Evidence also exists that red light stimulates stomatal opening by a slightly different mechanism. My own opinions Photosynthesis is best by blue and red light but different pigments helps the plant to use other colors as well. I believe that when choosing light one should avoid red light above 700nm as much as possible by removing all incandescent lightsources ( except when etiolation is wanted). After that it is more a matter of how much light we can give our plants and not so much about color. The main reason to mimic daylight is that our plants look more beautiful under it. Then looki att prices and design of fixtures and lumens/watt. Metal Halide looks good as daylight but HPS is more efficient lumens/watt (but ugly-yellow). 250-400W is good economy but needs distance from plants because of large amount of concentrated heat radiation. I prefer Biolux fluorescent tubes (mimics daylight) but they are almost too expensive. If you want good photosynthesis but feel that bright light would be annoying in your room GroLux = FLUORA by Osram is a good option. =color 77 SUMMARY Said that, I do believe that ANY cool fluorescent light would be an exellent light source. I am sure that 2 cool-whites is better that 1 GroLux, and much cheaper. The amount of light is more important than color exept if red above 700nm! Blue (actinic) light can be used to make plants open stoma and/or orient towards that light Remember to add CO2. ( Indoors :-) ) Normal air only contains about 0,03% so any addition would be appreciated! sincerely, Anders Espefalt Sweden

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