The HID in HID lights implies High Intensity Discharge. This kind of lighting requires a separate power supply to run it, but it is much like conventional light bulbs. HID bulbs are usually used for the flowering cycle of the vegetation, while a CFL is used for the first stage. Although it seems like a lot, the same setup and power supply can often be used for each bulb, so it is easy to switch the setups out mid-season. The HID bulb gets fairly hot as well, and proper ventilation is necessary to both not burn the plants and stop hot air buildup. HID bulbs are getting cheaper as a result of interest by NASA, though. Despite these negatives, this sort of setup offers the most amount of light out of a single fixture.
An LED grow light method is unique in many ways. Power is significantly reduced while using LED bulbs, and the light output is not sacrificed whatsoever. HID grow systems pull many hundreds of watts and can be extremely expensive to have on in certain areas. Running a whole grow light setup costs less per month and offers an optimized color spectrum for what plants have to have the most. Since LEDs are quite small, many high powered ones are utilized in grow lights, and colors are usually mixed and matched carefully. Growing can be complex, and using a single light fixture the full time can save a lot of headaches. LED's are also much healthier for people, because they produce very little harmful UV and warmth when running. LED bulb setups are also anticipated to last about seven to ten years, so they are thought to be long term investments. LED technology is just now getting started and is rapidly becoming better, but HIDs still hold the highest intensity capabilities. Fortunately, current LED systems are good enough for almost everything.
Many businesses that sell these setups also create them themselves. When purchasing LED setups, these companies become more important, because most vendors must have good reputations.