Sylvania Lumalux S51 400W LU400/ECO (67533) High Pressure Sodium Lamps are intended primarily for use in enclosed luminaires. Initial Lumens 50,000, Mean Lumens 45,000, Rated Average Life 24,000 Hours based on 10 hours per start, ANSI Ballast Type S51. These Sylvania Lumalux HPS Lamps employ a Mogul Base and are designed with an ET18 bulb.