Sunlite 30315-su f21t5/830 21w fluorescent t5 bulb, mini bi-pin, warm white the fluorescent 21 watt 3,000k warm white t5 high performance straight tube features a mini bi-pin base, provides a light output of 1,900 lumens at a color rendering index (cri) of 82 and can last an average of 20,000 hours. These lamp utilize a single and double coat phosphor system. Series lamps have an increased cri due to the use of tri-phosphors (rare earth phosphors). Tri-phosphors also increase the lumens/watt output of the lamp. These series lamps offer superior quality of lighting, increased energy efficiencies, and extend life.