Note 56. HID Lighting
The Energy Efficiency Manual includes a group of energy conservation measures related to high intensity discharge (HID) lighting. This Note explains the essentials of HID lighting.
HID lighting is a category of that includes three distinct types of lamps, mercury vapor, metal halide, and high-pressure sodium. Low-pressure sodium lighting, which is similar to HID lighting, is covered also. There are large differences in efficiency, color rendering (CRI) , and other important characteristics among these types. The Note explains the factors that cause these differences.
The Note begins by describing how HID lighting works, including the role of mercury vapor in all the types, other metal vapors, inert starting gases, buffer gases, and operation at high temperature. The construction of HID and low pressure sodium lamps is illustrated, including the arc tube, electrodes, special glass tubes, phosphors, and other features.
HID lamps require accessories, including ballasts, ignitors, and special fixtures (“luminaires”). Ballasts are needed to limit current and aid starting. The types of HID ballasts are illustrated. Ignitors are a starting accessory that is required for some high-pressure sodium and metal halide lamps.
The characteristics of mercury vapor lamps, metal halide lamps, high-pressure sodium lamps, and low-pressure sodium lamps are described. These include efficiency or efficacy (lumens per watt), color rendering or CRI, mounting positions, starting times and restarting intervals, safety features, lumen degradation or depreciation, wattage range, and the relationship of efficiency to wattage.