F13W/840 fluorescent T5 tube 18\" Triphosphor light bulbs - 4000K Cool WhiteTube length: 21\" - 517mm (530mm with pins)Fitted with a standard sized G5 2-pin (5mm apart) caps to both ends.This triphosphor fluorescent T8 tube provides a superior quality of light, with greater energy efficiency and a longer life. Unlike a standard tube, triphosphor tubes retain their high quality of output throughout their lifetime. With uniformly good colour rendering illuminating objects in their natural light, these tubes are ideal for shop lighting, as well as for high-quality lighting in the office and home.Rated lifetime of 5,000 hours (That\'s around 3 1/2 years of light, based on average use of 4 hours per day).NB - This replaces the older, less efficient Halophosphate tube.Need more help in choosing a suitable fluorescent tube? Read our guide Choosing Flourescent Tubes and our guide to Flourescent Starters.