Posted 14 July 2012 - 05:06 AM
Do you mean you want to make a LED light source to grow plants under?
Commercial units use a mixture of red and blue LEDs. There's no green used because chlorophyll doesn't absorb green, it just reflects it, which is why most leaves look green.
Fluorescent Grow-lights have a mixture of red and blue phosphors, which is why they have a vivid purple appearance. If you use white lights to grow plants you'll be wasting power generating a green component that plants don't use.
Good LED spotlights and studio lights are expensive mainly because it's hard to make natural-looking white light with LEDs. Same with fluorescent lights.
Plants don't care overmuch about the exact wavelength, so any sort of efficient RED and Blue LEDs will do.
However, plants still need a lot of illumination, because they're used to photosynthesizing in daylight, which can be hundreds to thousands as times as bright as normal interior lighting.
Commercial "closed" hydroponic operations use thousands of high-efficiency red and blue LEDs, and they're so bright that the operators have to wear safety goggles in case they look directly into the LEDs.
Even then, the overall illumination is still fairly weak compared to midday daylight, but it makes up for it by being on 24/7.
Anyway, why do you want to use LEDs? For a large installation, they're worthwhile because of the power saving, but for a small-scale operation you're likely to find that fluorescent grow-lights are more cost-effective. It doesn't matter what you use though; the power consumption is still going to be significant.