50/50 compact fluorescent daylight & actinic lamp from ESU. Half of this bulb outputs 10,000K daylight, strong white with a slight blue cast, perfect for saltwater and reef organisms accustomed to intense daylight. The other half provides the necessary actinic supplementation - actinic blue wavelengths are needed by marine organisms because they travel further in the water, and they are used by symbiotic reef algae for photosynthesis vital to proper coral growth.
Power compact bulbs produce more lumens per watt than any other fluorescent bulb, a great lighting solution for all but the most light intensive reef setups. Easy to install, energy efficient, and long-lived. Use with a compact fluorescent fixture or with appropriate ballast.