The 41 or 21 watt Bloom iSunlight T5 HO replacement LED lamps are an excellent choice for the complete cycle of your plants' life. The iSunlight T5 Bloom lamp is an intelligent LED that is specifically designed to work with your existing T5 HO fluorescent fixture. These T5 LED retrofit lamps make an excellent replacement for all 3,000 K T5 fluorescent lamps. The iSunlight Bloom features a combination of 450 nm blue, 660 nm red and 5,500 K full spectrum white diodes while consuming only 21 watts of power for the 2 ft lamp and 41 watts of power for the 4 ft lamp. Environmentally friendly, mercury-free LED lamps. Not compatible with HF Agrobrite T5 fixture.