“NDA” No Dark Area Helios Standard light fixtures that use standard American light bulbs available in the states are not made to illuminate the complete aquarium. In fact, a 24 in. bulb is used in a 36 in. aquarium kit thus 30% of the aquarium is without light. Helios HO T5-IV Fixtures are custom tailored with Universal Euro size bulbs, meaning it lights your aquarium completely from end to end.Enhance the natural color of your fish, plants and coral with Helios T5 HO lighting. Helios presents economical color-rendering bulbs available for freshwater, planted, reef and marine aquariums. All have received verified Kelvin ratings. Published ratings based on lab tests under controlled conditions. T5 lamps have a high power factor and high lumen output. SPECIFICATION: Fixture Size : 24 watt - 24 in. Total Wattage: 1 x 24w. Bulb Color: Daylight 11,000K . Use for: Saltwater & Freshwater. Fixture Dimension ( L x W x H (inch) : 24 x 4 x 2.75 in. Standard Bulb Size: 24w - 21 in. INCLUDES: One Single HO T5 Light Fixture and 1 Piece of T5 HO Lamps. Note: The color of the item may vary slightly due to photography and your own computer.