Indoor plants need more than natural light from windows to grow and produce. Special purpose grow light systems provide that light with a bulb, a reflector and a ballast containing a capacitor, transformer and regulator. Three common types of grow lights are metal halide (MH, the most popular), high pressure sodium (HPS) and fluorescent. Once the seedlings have matured, indoor gardeners may change their grow light system to HPS, whose red color spectrum emissions encourage production of vegetables and flowers.
Carefully measure the area requiring primary coverage from the grow light.
Select the type of grow light and wattage needed to cover your growing space. The Little Greenhouse recommends 250 watts for a three foot by three foot space, 400 watts for five by five, 600 watts for six by six, and 1,000 watts for eight by eight foot coverage. If your space is larger, you will need multiple grow lights to provide adequate coverage for your plants.
Purchase a grow light system or separate components to construct your own system. Be sure to match the ballast and reflector to the type of bulb and wattage you have chosen.
Mount your grow light and reflector above plants -- usually suspended from the ceiling. The greater the wattage of the grow light, the higher the light source should be above the plants. The Little Greenhouse recommends 9 inches to two feet for 250-watt bulbs, progressing to six feet for 1,000-watt bulbs.
Install a light timer. Plants grown indoors need both periods of light and periods of darkness. Set your timer to about the equivalent number of light hours the plant would have growing outdoors in late spring and summer -- about 14 hours.
Set up a fan to cool the plant area if ambient heat from the grow lights exceeds recommended temperatures for growing the types of plants in your grow box -- 65 degrees for cool season crops and 85 degrees for warm season crops.