There's lots of arm waving about frequencies with little hard facts and there is quite a bit of unconnected knowledge. There are two types of chlorophyll and each absorb light in two different fairly narrow frequency bands that are slightly shifted from each other. I have found no information whether they just absorb these frequencies or they really need both, or whether these are complementary chemicals to use more of the available light. Perhaps you only need to activate either one for proper plant growth.
The proportion of different frequencies in sunlight differs with the season and direct sun v.s. shade so some ratios are better for growth and some promote flowering. I have seen completely opposite suggestions and experimental results for different ratios. Much of the scientific research is based on chemical absorbtion, which may or may not be directly related to conversion.
Many of the commercial lights for sale use wide angle LEDs which can be placed close to the plants if you only want to stimulate the leaves at the top of the plant. At double the distance you get 1/4th the intensity. A wide angle designed to be placed a foot from the top will only supply a 1/16th as much light to bottom leaves on a 2 foot tall plant.
No LEDs exactly match the chlorophyll absorbtion band but some are close. It's also not clear if close is good enough.
Leaves are green because they don't absorb green light. If the grow light output were perfect the plants would appear black. Sodium vapor lamps put out lots of light and are quite efficient overall but most of their output is wasted. I have not seen any comparison of different lights that compares usable light.
This is just off the top of my head. I have more specific information I gathered for an aborted grow light project, including samples of research, spec evaluation of some off shore LEDs and prices, and so on if anyone is interested. I would have to find it and it's about a year old. It's quite a few pages. If anyone's interested how would I post it?
- Stephen
