High intensity discharge (HID) lights
There are several different types of HID lights including mercury vapor, metal halide, high pressure sodium and conversion bulbs.
Metal halide and High Pressure Sodium lamps produce a color spectrum that is somewhat comparable to the sun and can be used to grow plants
Metal Halide- Metal halide bulbs are a type of HID light that emits light in the blue and violet parts of the light spectrum, which is similar to the light that is available outdoors during spring.
Metal Halide- Metal halide bulbs are a type of HID light that emits light in the blue and violet parts of the light spectrum, which is similar to the light that is available outdoors during spring.
High Pressure Sodium lamps (HPS)- High-pressure sodium lights are a more efficient type of HID lighting than metal halides.
HPS bulbs emit light in the yellow/red visible light as well as small portions of all other visible light. Since HPS lights deliver more energy in the red part of the light spectrum, they may promote blooming and fruiting.
This same spectrum affects plants grown under HPS lights by tending to elongate or cause the plants to “stretch” from the lack of blue/ultraviolet spectrum of the light created.