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HID Lighting for the Home Grower
There are four basic types of high intensity discharge (HID) lights. The oldest and the most used for general lighting up to the mid-’70s was mercury vapor. Metallic (or metal) halide and high pressure sodium are basically variations of mercury vapor bulb, using different metals in the vapor tube. Halides started to replace mercury vapor for general lighting, but because of their higher efficiency sodiums now have 70 to 80 percent of the market. Low pressure sodium bulbs (LPS) are similar, but use no mercury in the arc.