Leds do work. Most of the existing units for sale are snake oil type units. Especially the ones being show 3 feet plus over the tops of plants.....
The losses from HPS and MH bulbs are well, well documented. Plants have very specific spectrums that they prefer. Leds should be chosen to match those needs... kinda like adding the right amount of Micro and Bloom when using GH nutes.
My seedling unit is posted at TheCannaCabana.com
264 very tightly controlled current leds lighting up a roughly 14x9 box that holds 24 - 2" net pots that hits the power line for a whopping 12watts.
White leds are virtually useless for growing. Wrong spectrum