Supplemental lighting is used in greenhouses to increase crop production during time periods with low levels of solar radiation. ... Thus, if crop production is on a tight schedule, supplemental lighting may be required year-round.
Fruit-bearing crops and flowers need more light than root vegetables and greens.
The most efficient lamps used for supplemental lighting in greenhouses are the so-called high intensity discharge (HID) lamps. Metal halide (MH) lamps produce a more white-colored light, while high-pressure sodium (HPS) lamp light is more yellowish orange. MH lamps produce a little more blue light that is important for the proper development of some crop species.