The best light bulb for growing your plants will depend on your indoor garden space, budget, and horticultural goals. HPS and MH bulbs are the simplest lighting technology available, and are great for large spaces. These HID grow lights cover a large amount of space, but burn hot.
CMH and LEC bulbs are the newest and most efficient HID lighting technology, with drastically increased efficiency, lower heat output, and a higher quality of light over MH and HPS grow lights. These bulbs also last over two times longer than other HID bulbs!
Fluorescent bulbs and tubes are the best light for propagation, since they are lower intensity and HID and LED systems. Fluorescent grow lights are commonly used by those growing in tight spaces, as these operate at lower temperatures and are less likely to burn plants.