Grow lights are fluorescent tubes, incandescent lamps, LED fixtures and other technologies that produce light with the correct color spectrum and intensity for growing plants. Inexpensive grow lights can be made at home from commonly-available shop-light fixtures, while more sophisticated fixtures from specialty retailers can cost hundreds of dollars. Some grow light lamps fit ordinary household fixtures, while others require special housings.
Fluorescent lamps can be used for starting seedlings and rooting cuttings. Many gardeners use a combination of one cool-white tube with one warm-white tube (in a regular 4-foot shop light fixture) for these purposes. Several brands of fluorescent tubes are specially designed to produce something close to the full color spectrum of light that plants require. Fluorescents do not have sufficient intensity to meet the needs of mature plants.
Among the fluorescent tube grow light brands available are Sylvania Gro-Lux, GE Chroma 75, Hydrofarm T5, AgroSun, Tek-Light High Output T5, Verilux, and Spectra 5900.
Compact Fluorescent Lamps
Originally introduced as an energy-efficient alternative to conventional incandescent lamps, two compact fluorescent lamps (CFLs) are now available for use as a grow light. The Hydrofarm Full Spectrum Daylight lamp produces a natural-appearing light, while the Hydrofarm Full Spectrum Warm lamp gives light that has more orange and red. According to Hydrofarm, a leading manufacturer of hydroponics and grow lights (hydrofarm.com), "The red spectrum stimulates flowering and fruit production."
Metal Halide Lamps
This is a high-intensity-discharge (HID) lamp that produces light by arcing electricity through a mixture of metal halides. The white-blue spectrum light stimulates vegetative growth. This is the best bulb for the first stage of plant growth. AgroSun is a metal halide bulb manufactured by Hydrofarm, which puts out 38 percent more light in the red portion of the spectrum than regular metal halide lamps.
Sodium lamps emit light in the yellow/red/orange regions of the color spectrum. Hydrofarm notes that "many indoor gardeners switch to sodium lamps when it is time to induce flowering or fruiting of their plants."
Most incandescent bulbs are not suitable for plant growth. They do not produce light in the color spectra needed by plants, and too much of their energy use produces heat which can be harmful to young plants. However, the AgroSun Dayspot incandescent grow lamp can be used for bonsai, terrariums or small indoor herb gardens. It fits in any regular incandescent fixture.
LED Grow Lights
Light emitting diode (LED) lamps produce light in the blue and red spectra, and are very energy-efficient. Unlike many other lamps, they do not contain mercury, and produce very little heat. For these reasons they are considered likely to become the leading type of grow light in the future.