There are three different types of lights that are used for indoor growing: Florescent, Metal Halide, and High Pressure Sodium. There are advantages and disadvantages to each.
Florescent lights are convenient because they are very energy efficient, cheap, and they do not generate too much heat. Unfortunately, they don’t really put out enough lumens to make growing with them worthwhile. Plants grown under fluorescents stretch more than others, and the bud they produce is very airy. The only good use for these is to keep clones and mother plants.
High Pressure Sodium (HPS) lights are a grower’s bread and butter. If you are only planning on buying one light, buy an HPS. They produce a lot of heat and take up a lot of power (they run between 125 and 1000 watts), they provide the best spectrum and most intense light for a flowering plant.
Metal Halide (MH) lights are used by some growers in veg, since they provide a more appropriate light spectrum for vegetative growth than HPS. It is not recommended, however, to have a MH as your sole light. They vary from 175 to 1000 watts.
LED lights are just starting to become widely available. They can be tuned to produce the exact spectrum of light a plant wants, they take less than 1/6 as much power as an equivalent HPS, and don’t produce heat. Unfortunately, the technology is new, and therefore expensive. But if you have the money, this is the future of growing.
Sizes, coverage and space between plant and light (HPS):
250w: 3’x3′, 12″-18″ away from plants
400w: 4’x4′, 12″-24″ away from plants
600w: 4’x4′, 18″-24″ away from plants
1000w: 6’x6′, at least 24″ away from plants
These sizes and distances can change with different reflectors, and
even between different specific lights.
Reflectors are a hugely important investment, as they reduce hotspots and therefore allow you to hang your light closer to your plants. The difference between a good and a poor reflector can mean an almost 100% increase in your harvest.
It is suggested to buy your ballast when you buy your lights, so that you can be sure they match. Ask your salesperson for help determining which ballast to get.
When hanging your lights, make sure that they can be moved up and down. You will need to keep them a constant distance away from the plants, but the plants grow, so you will need to be able to raise and lower your lights.
Water and light proofing
Make sure your growroom has absolutely no water or light leaks. If your floor is not waterproof, the structure that your growroom is made out of will slowly start to rot. I suggest pond liner on the floor of the room, though there are many ways of going about this. Light proofing is even more important. If there are light leaks into your growroom during the 12-hour dark period, your plants will be caused undue stress and may hermaphrodite. To check for light leaks, stand in your room with the lights off, and let your eyes adjust for a couple minutes. Then check and fix light leaks with tape. Also, make sure that the walls of your room are reflective. Either cover them with Visqueen, or paint them bright white.