Bulbrite MH100/U/MED Medium E26 Base 100-Watt Enclosed Fixture Metal Halide Pulse Start Light Bulb, Universal Burn Long Life (7,500 hours) Perfect for commercial, industrial, security and outdoor lighting applications For use in enclosed fixtures only Pulse Start: Quicker Start/Restrike, Improved Lumen Maintenance, & Increased Efficacy Available for use in enclosed or open fixtures