The 41 or 21 watt 5,500?K T5 HO replacement LED lamps are an excellent choice for the propagation and veg cycles of your plants life. The iSunlight? T5 lamps are an intelligent LED that is specifically designed to work with your existing T5 HO fluorescent fixture. The iSunlight? 4 foot lamp produces over 4,900 lumens with only 41 watts of consumed power and the 2 foot lamp produces over 2,400 lumens with only 21 watts of consumed power. These are environmentally friendly and mercury free lamps.