A Grow light is an electric lamp designed to promote plant growth by emitting an electromagnetic spectrum appropriate for photosynthesis. It emits a light spectrum similar to that from the sun, allowing indoor growth with outdoor conditions. more...
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/orange 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 flow of current flowing to the light. This is required because of the high intensity of the light that is necessary to produce something akin to sunlight.
Lamp types used as grow lights include high-intensity discharge lamps, fluorescent lamps and LEDs. Grow lights are most used for indoor gardening, including indoor hydroponics and aquatic plants.
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.
The bigger the plant gets the more light it requires; if there is not enough light, a plant will not grow, regardless of other conditions.
For indoor gardening one of the most important topics is light density, measured in lux. Light density is the amount of light incident on a surface. One lux equals one lumen (unit) of light falling on an area of one square meter. A brightly lit office would be illuminated at about 400 lux. In Imperial (pounds-feet) terms, a foot-candle, or the intensity of a standard candle on an area of 1 square foot, is about 10.76 lux.
Cool white fluorescent lamps are sometimes used as grow lamps. These offer slightly lower performance, a white light, and lower purchase cost.
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