LEDs are the future. I have been experimenting with them with a lot of plant species (not for growing my favorite plant though) for the last year in multiple settings. The problem with most "LED grow light" out there is the limitation in their spectrum. People who designed these lamps are focusing only on the absorption spectrum of chlorophyll and it's a big mistake. RED and BLUE should compose 70% of the lamp spectrum, but providing some white light with a complete spectrum is also important.

LEDs are definitively the future of lighting in general, including horticulture. Their efficiency is increasing every year by about 20% and the price are going down even faster. So it's only a matter of years before the white LEDs beat the best HPS out these in term of Lumen / watt with reasonable pricing. Concerning pricing, always keep in mind that LEDs will last more than 50,000 hours. That's 11 year at 12h per day. In term of "plant Lumen" or "PAR" per watt, some LEDs are already beating HPS lamps. A lot of light from an HPS is "wasted" (in heat / infrared, UV) and a main part of their spectrum is in the yellow / green region that is perceived as really bright in our eyes, but not the most efficient for plants photosynthesis. Lumen is really a poor measure for the plant grow potential of a lamp.