Metal Halide Aquarium Lighting Basics
Metal Halide lighting is high output aquarium lighting, and is the most able to reproduce natural sunlight. Metal Halides are a High Intensity Discharge (HID), gas discharge lamp. Light is produced by an electrical arc within a glass tube, which has a gaseous mixture of mercury and metal halide compounds. Unlike the diffused light produced by Fluorescent lights, Metal halides produce a point source light, which is why you get the “rippling” or “shimmer” light effect with Metal Halide bulbs. Metal Halides are high power, extreme heat producing bulbs, proper ventilation, and the use of a chiller is recommended when using these bulbs.
Metal Halide bulbs come in several styles for aquarium use; The two most common are the a single ended screw in type, or mogul, base connection, and the double ended, or HQI, style bulb. Less common is the G-12 dual pin base type of HID bulb. Metal Halides are available in most popular Kelvin ratings, and from 70-1000 watts. The different styles of Metal Halide bulbs are designed for specific fixtures, and each wattage bulb requires specific ballast for operation. Some ballasts can power either style of bulb of the same wattage. Metal halide bulbs should be replaced every 8-12 months, for maximum performance. Metal halides are best used on medium to large size aquariums, and are recommended particularly for planted and reef aquariums over 24” deep, because of the intensity, and replication of natural sunlight, that metal halide lights are capable of.