I copied this for those interested....
Pros and Contras LED Grow Light Systems
There are some pro and contras when it comes to LED grow light systems. When planning such farming alternatives, one has to carefully consider that plants do use light at all wavelengths from UV to IR, as explained above, needed to convert water and carbon dioxide into sugars. Some plants use more red and blue, less green and yellow, while others use green as much as they use red and blue, as well as the light in between. If LEDs are chosen for brightness, there is one aspect to be underlined: they just look bright because their light is unidirectional and their size is small. To get enough light there are many LEDs needed, thats why the cost of LED arrays or LED modules is so high. LEDs can be calibrated to emit only the light most efficient for the plants, but not all the light plants need. This is why such light sources are recommended only in places where direct light from the sun is not enough or inexistent space farming for example. Also in places where light from the sun is too strong and can harm the plants with the high emission of UV, LEDs are a good choice, because UV filters are stopping some of the useful wavelengths too. In wintertime the weather conditions restrain crop production this is why greenhouses need a substitute for the natural light. It makes sense to deliver plants the minimum lighting conditions for a corresponding evolution.
There are some significant factors to take into account when choosing light sources for such applications and these are low costs, energy efficiency, long life, and ability to withstand voltage fluctuations, modularity in order to grant users the possibility to assemble arrays that gives as much light as needed, where needed. LEDs are pretty efficient in the conversion of electric power to light, in any case more than traditional fluorescent and incandescent lamps. Due to the fact that light emitting diodes can be manufactured to emit a specific wavelength and are expected to have a long life span (from 50000 hours up), many plant physiologists are considering using them in large applications. Compared to LEDs most of the other traditional lamps have to be replaced every two-three years. Other features such as choice of viewing angles, control options, instant turn on times, cold start and much more, recommend the semiconductor devices. At present this is still an expensive technology, but in time LEDs efficiency will be maximized while prices reduced and these details are a good base for future planning.
The future's so bright..........I'm gonna get paid!!!!