GE's T8 LED tubes replace 18-inch T81-inch diameterfluorescent bulbs using the existing fixture and electronic ballast. It's slim size fits in the same fixtures as traditional 18-inch T8 fluorescent bulbs. Why make the switch to LED? GE's LED tubes are rated to last 36,000 hours. They provide long 16-year life based on six hours use per day, so you'll replace less often.