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To power an HMI bulb, special ballasts act as an ignitor to start the arc, and then regulate it by acting as a choke. Two types of ballasts exist: magnetic and electronic (square-wave or flicker-free). Magnetic ballasts are generally much heavier and bulkier than electronic ballasts, as they consist primarily of a network of large inductors ...
High-pressure sodium lamps are quite efficient—about 100 lumens per watt, when measured for photopic lighting conditions. Some higher-power lamps (e.g. 600 watt) have efficacies of about 150 lumens per watt. Since the high-pressure sodium arc is extremely chemically reactive, the arc tube is typically made of translucent aluminum oxide.
Ballasts for discharge lamps Like fluorescent lamps, HID lamps require a ballast to start and maintain their arcs. The method used to initially strike the arc varies: mercury-vapor lamps and some metal-halide lamps are usually started using a third electrode near one of the main electrodes, while other lamp styles are usually started using ...
A metal halide bulb produces 60-125 lumens/watt, depending on the wattage of the bulb. [24] They are now being made for digital ballasts in a pulse start version, which have higher electrical efficiency (up to 110 lumens per watt) and faster warmup. [25] One common example of a pulse start metal halide is the ceramic metal halide (CMH).
[1] [3] To prevent this, fluorescent tubes are connected to the power line through a ballast. The ballast adds positive impedance (AC resistance) to the circuit to counteract the negative resistance of the tube, limiting the current. [1] Several American magnetic ballasts for fluorescent lamps. The top is a rapid start series autoregulator ...
Mercury-vapor lights operate at an internal pressure of around one atmosphere and require special fixtures, as well as an electrical ballast. They also require a warm-up period of four to seven minutes to reach full light output. Mercury-vapor lamps are becoming obsolete due to the higher efficiency and better color balance of metal halide ...