A grow light is an electric lamp designed to promote plant growth by emitting an electromagnetic spectrum appropriate for photosynthesis. The emitted light spectrum is similar to that from the sun, allowing indoor growth with outdoor conditions. Natural daylight has a high color temperature (approx. 6000 K) and appears bluish. Through the use of the color rendering index, it is possible to compare how much the lamp matches the natural color of regular sunlight.
Light spectrums used
Different light spectrums are used for the different stages of plant growth. The initial vegetative stage requires blue spectrum of light, whereas the later "flowering" stage is usually done with red¨Corange spectrums. The lights can be bought by spectrum colour specifically, or some companies such as Sylvania Grolux produce a full spectrum bulb which caters for all stages of growth.
The light is usually used in conjunction with a reflector, to control and intensify the light emissions, and will include an electrical ballast to control the current to the light. This is required because of the high intensity of the light that is necessary to produce something akin to sunlight.
Types & set-ups
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 blui
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