Metal Halide Bulb Information

There are three main considerations to decide upon when choosing Metal Halide bulbs and systems: Type of bulb, Wattage and color temperature.

There are two different types of bulbs available within the metal halide family. First are the single ended bulbs or also referred to as mogul based or abbreviated SE. Single ended lamps will have a thread ended like a normal light bulb only a little thicker and will screw into a mogul socket. These bulbs are most commonly seen in 175, 250 and 400 watt but are also occasionally available in 150 and 1000 watt versions. The SE bulbs have a glass tube around the arc tube (the part that lights up) to help protect them. This glass will provide UV protection and the bulbs do not need another protective shield when placed over the tank. But if you have fish that tend to splash the extra protection of a glass shield could prevent the bulb from breaking. Single ended bulbs are the most common metal halide bulbs being used and will have the most types of bulbs available (currently).

The second types of bulbs available are the double ended bulbs (abbreviated DE). DE bulbs lack the threads and UV casing found on SE bulbs. Instead they will be held in place using two ceramic endcaps that the bulbs snap into and the pendant or fixture that houses the bulbs will have a UV glass shield. DE bulbs should never be run over a tank without the use of the glass shield. While DE bulbs are newer to the industry they have made leaps and bounds since they were introduced and are becoming more and more popular. This popularity is mainly due in to the fact that when compared watt to watt to SE bulbs they will have a higher PAR value (P.A.R.- Abbreviation for Photosynthetically Active Radiation. Used in measuring the light levels or energy given off by a lamp). Most commonly you see the DE bulbs in 150 and 250 watt bulbs but there are 70 and 400 watt versions also available.

There are generally two considerations when planning wattage, tank depth and the requirements of various types of corals. For SE bulbs, tanks 18" and shorter it is recommended to use 175. For tanks 18-24” deep 250 watt bulbs are recommended and tanks 24" and over will use 400 watt MH bulbs. I have found most soft and large-polyped-stony corals to do just fine within 5-15 inches from a 175 watt bulb and 10-24 inches from a 400 watt bulb. Most small-polyped-stony corals survive within 5-10 inches from a 175 watt but appear to thrive within 5-15 inches of 250 and 400 watt bulbs. For DE bulbs it is generally recommended for tanks 22” or shorter to go with 150 watt and for tanks 22-30” deep to use 250 watt bulbs. 70 watt DE bulbs can be used for tanks under 15” deep and for tanks over 30” deep 400 watt DE bulbs are usually recommended. These are all just general statements to assist in going the correct route with choosing wattage. Water clarity and quality will also play a big factor in allowing light to penetrate deeper in the tank.

Color temperature is a hotly debated topic where there is no one recommendation that will fit everybody. Lowers Kelvin temperatures are more yellow and green in color while higher Kelvin temperatures are more white and blue in color. There are two factors that determine most hobbyists choice of bulb colors, par rating and aesthetics. The 6500K Iwasaki bulb is generally regarded as an excellent PAR rated bulb. However, its green tinged yellowish color makes for what is considered by many as poor aesthetics. This is not the say the much bluer 20,000K German bulb is aesthetically ideal. Many hobbyists complain this bulb is too blue. By far, the bulbs most popularly purchased are ones rated between 10,000K and 15,000K. The majority of hobbyists choose aesthetics as the determining factor of choosing color temperature for the primary reason that the appearance of our aquariums is of utmost importance. Due to the subjective nature of color preference, we refrain from making suggestions on which color temperature is right for you. Instead, we have a visual bulb comparison of some of the most popular SE bulbs on the market.

As a general rule of thumb, use one metal halide bulb for 24" of tank length.

Metal Halide bulbs are one the most difficult aspects of the hobby to recommend. Most of the information here is general.