Sunlite 05745-su fc40/2c/41k 40w fluorescent t5 double circline bulb, gu10q, cool white the fluorescent 40 watt 4,100k cool white t5 double circline features a gu10q base, provides a light output of 2,800 lumens at a color rendering index (cri) of 82 and can last an average of 10,000 hours.