For gardeners who find their indoor plant growth isn't what they would like it to be, the solution may be grow lights. Though grow lights are most often used in commercial greenhouses, homeowners and recreational gardeners can opt for them if the ambient lighting indoors isn't enough for their plants.
Full spectrum lights include metal halides and fluorescents. Metal halides provide the closest equivalent to natural light. High-pressure sodium lights provide light toward the red end of the spectrum. T-5 lights mirror fluorescents in many ways, but provide more light more efficiently (see Reference 1).
Light at the blue end of the spectrum, such as that provided by full spectrum lights, promotes vegetation and stronger stems. Light at the red end of the spectrum, such as that provided by high-pressure sodium lights, is better for promoting flower development. The type of light you choose may be determined by what type of plants you have and how close they are to blooming (see Reference 2).
The choice of light bulbs may be limited by the fixture. If you are using a metal halide bulb or high-pressure sodium, you should replace the bulbs every two or three years, even if they are not burned out. The older the bulb gets, the less effective it becomes because the light output diminishes (see Reference 2).
Most plants need at least 12 hours of light a day to flourish (see Reference 2). Getting less than 12 hours could send some plants into a dormant period, since light is one way plants recognize seasons. Many gardeners who use grow lights put them on a timer to ensure adequate light.
Some grow lights can become extremely hot and should not be placed too close to plants. Fluorescent lamps, however, are generally cool enough to be used in close proximity to foliage. If you are using grow lights, you may have to water more than you normally do because the lights can dry out the soil.