Also known as lead style ballasts, Constant-Wattage Autotransformer (CWA) ballasts are the most common ballasts used on 175 W or higher MH lamps. It offers the best compromise between cost and performance, means of providing stabilized light output (lamp regulation) as opposed to the Magnetically Regulated circuit. The circuit consists of a high reactance autotransformer with a capacitor in series with the lamp resulting in a high power factor ballast. Shows a typical Constant-Wattage Autotransformer (CWA) HID Ballast Circuit Diagram. This circuit requires an ignitor for QMH (Quartz Metal Halide) pulse start, CHM (Ceramic Metal Halide) and HPS (High Pressure Sodium).