XM Compatible 250 Watt 20000K 110V Metal Halide Bulb, E39 /E40 Mogul Screw On Base 20K 250W, , E39/E40 Screw Base Probe Start Ballast Color Spectrum: 20,000k (Kelvin) Vivid Blue ANSI Codes: M58, M58E Length: 8.3" , Bulb Shape: T15, E39/E40 Screw Base Operates on a Probe Start or Electronic Ballast