Replaces 34' 39W T5 HO lamps. Fits into fixtures just like a T5 HO bulb. Lower power consumption. Only uses 12 watts. Due to electricity cost savings the lamp will pay for itself in one year. Pleasant shimmer effect. Even daylight look for saltwater aquariums. Reduced heat. Much less heat than T5 HO lamps. We do not recommend using this LED Lamp in a fixture with metal halide bulbs. The heat from the metal halide bulbs could melt the Arcadia LED Lamp housing causing the lamp to fail.