175 Watt 20000K Metal Halide Aquarium Reef 175W 20K Mogul Mogul Screw E39 Bulb Lamp Color Spectrum: 20,000k (Kelvin) Vivid Blue ANSI Codes: M57, M57E, M57/E Length: 8.3" , Bulb Shape: T15, E39/E40 Screw Base Operates on a Probe Start or Electronic Ballast