Over the years I have grown my bonsai plants in windowsills, under incandescent light, fluorescent lighst or metal halide high intensity lighting. The best results up to now are clearly growing under metal halide lights. The downsides of metal halides are relative inefficiency with lots of heat released as a by-product and thus higher electrical bills as a result. Some years back I did use and test a commercial LED light in the early day of LED lighting that proved to be toxic to my plants. http://www.bonsaihunk.us/info/LEDvsFluoresc.html

Recently I purchased an LED light from ActiveGrow LED lighting. This is a 300Watt unit with about 180 individual LED lights. It replaced a 4 tube 4 foot long fluorescent light that was growing herbs for our daily consumption. The herbs are growing in a window box in a hydroponic growing system. On the left side remains one of the two original 4 tube fluro lights but on the right side I replaced the fluorescent with the ActiveGrow LED light fixture. Over the last 3-4 weeks the comparison of the growth of the plants on the LED side is 2-3 better than the old fluorescent left side. The growth is thicker, leaves more colorful and leaf texture much firmer indicating ideal growing conditions.

Herbs growing in a hydroponic growing system, right side LED and left side fluorescent lighting

I have to reconsider the use of LED lights for my plant room where I grow my bonsai and have had them growing that way for over 17 years.