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 5,100 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.