Sunlite 05815-su fc40t5/sp830 40w fluorescent t5 circline bulb, 2gx13, warm white the fluorescent 40 watt 3,000k warm white t5 circline features a 2gx13 base, provides a light output of 3,350 lumens at a color rendering index (cri) of 82 and can last an average of 10,000 hours.