Fluorescent Lighting

Types of lamps used as grow lights include incandescents, fluorescent lamps, high-intensity discharge lamps, and LEDs.

Today, the most widely used lights for professional indoor flower and vegetable growing are HPS/SON (high pressure sodium) and MH (metal halide). These are types of HID or high-intensity discharge lamps. Normal metal halide bulbs have a slightly bluish light and are used for the vegetative phase of growth, as their spectrum is close to sunlight and encourages normal to slightly leggy growth. Unlike high pressure sodium lamps, metal halide lamps also produce ultraviolet radiation, which may play a role in increasing the amount, quality, and potency of herbs or other materials produced by plants. High pressure sodium lamps may trigger a greater flowering response in plants and are thus used for the second (or reproductive) phase of growth. If high pressure sodium lamps are used for the vegetative phase, plants will usually grow slightly more quickly, but will also have longer internodes, and may be longer overall. Metal halide bulbs with added reddish spectrum as well as high pressure sodium bulbs with added bluish spectrum are also available for added flexibility for use with both vegetative and flowering growth.