HID lighting systems represent the safest, most economical way of providing light for your plants. They are used all the time in parking lots, warehouses, baseball diamonds, football fields and other places where reliability and economy are a prime concern.
Systems used for garden lighting are constructed differently, but the features of dependability and cheap operation remain the same. Two common types of HID lighting have been adapted for safe use in the garden and greenhouse, Metal Halide and High-Pressure Sodium.
The most common lighting systems for indoor growing are of the High Intensity Discharge (HID) variety. HID lights are very popular among indoor growers because they have a very high light output, and provide light of the right part of the spectrum to promote plant growth. . The heart of an HID system is an arc lamp bulb and a ballast. The ballast serves to start and maintain the arc inside the bulb. Ballasts come in two types, mechanical or electronic. Electronic ballasts are more efficient than mechanical types, and often support multiple bulb types, adding to the versatility of your system.
There are two types of HID bulbs on the market, High Pressure Sodium (HPS) and Metal Halide (MH). The primary difference between the two types from a functional stand point is the color spectrum emitted by the light. HPS bulbs emit light in the red to yellow range of visible light while MH bulbs emit a more balanced light covering all the energy peaks of the visible light spectrum. To the eye, the light from HPS bulbs appears reddish orange, while MH bulbs throw alight that appears blue-white. These differences in spectral emission make these two bulb types suitable for different types of growth. With either bulb type, a reflector is generally recommended to utilize the light most efficiently.
HID bulbs of either type produce a lot of heat. Depending upon your growing circumstances this heat may need to be dissipated or vented. HID systems may be air cooled or water cooled.
