SunBlaster 24" (2 ft or 61cm)4 pack T5 HO Fluorescent Grow Light Replacement Bulb features a Full spectrum 6400K High Output intensity with just 24 watts power usage. SunBlaster T5HO (High Output) Replacement Fluorescent Grow Light Bulbs provide everything you need to get your plants growing like never before! Change those old fluorescent bulbs out for new high tech, high output Sun Blaster bulbs or replace broken ones. Each Sun Blaster T5 HO 6400K Full spectrum grow light bulb is designed for optimum growing results. All SunBlaster T5HO grow light bulbs are driven at the optimum temperature, lowering heat production and extending lamp life. The New Edition T5 HO fluorescent gow light bulbs have been re-engineered incorporating a "Cold Chamber" ensuring that the small amount of mercury gas contained is kept at the most efficient operating temperature to produce the maximum light output. SunBlaster T5HO fluorescent replacement bulbs are available in 2' (61cm) 24 watt 6400K, 3' (91cm) 39 watt 6400K and 4' (122cm) 54 watt, 6400K full color spectrum for vegetative growth. High Output 6400K lamps simulate natural sunlight and are ideal for cuttings or vegetative growth. SunBlaster's T5HO lamps produce a light of much greater strength than a conventional tube and as a result, the energy input into the area being lit is much greater and the light penetration is far superior to anything previously available. SunBlaster replacement fluorescent grow lights require a special T5HO Fixture and can not be used in standard fluorescent fixtures. Ideal for Aquariums, greenhouses, general office lighting, Sun Blaster T5HO bulbs are used to simulate average outdoor light conditions, horticulturalists choose the 6400K for the best vegetative growth.