Sunlite 05820-su fc40t5/sp835 40w fluorescent t5 circline bulb, 2gx13, neutral white the fluorescent 40 watt 3,500k neutral 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.