When and why to use metal halide aquarium bulbs

Almost all indoor aquariums have lighting of some kind. Most use traditional incandescent or florescent lighting because of the efficiency and convenience of this type of lighting. Under most circumstances these lights are all you will ever need and the majority of planted aquariums can thrive happily using this method.

But, if you really want a planted aquarium to thrive, have a deep tank, a marine coral tank or just want to be different, you can use alternatives like the T5 florescent or metal halide bulbs.

Mainly used in commercial applications, the metal halide bulb is specially designed to produce maximum light for minimal power. For the techies amongst you it works by throwing an arc of electricity across two electrodes through a mixture of argon, mercury and metal halide gases. The colour of the light is influenced by the mixture of metal halides in the chamber, producing a spectrum of light, and you can choose the effect you require when you purchase the bulb. This is, however, not guaranteed, as the colour of the light from the bulb will change through it’s lifetime. Some plants respond better to a certain spectrum of light, and this is where the colour affects the result.

Before you start thinking of these, there are a few points that need to be addressed. The most important of these is temperature. Standard lighting gives off very little heat, so doesn’t adversely affect the temperature of the water, but these high-yield bulbs give off a great deal of heat, and if they are fitted too close to the water, or not correctly ventilated, they will send the water temperature souring! The metal halide bulb works at around 2000 degrees Fahrenheit, and this has to be dispersed or the bulb itself will overheat. It also requires a special fitting and starter unit, similar to a florescent choke or ballast.

Because of these points, you will need to make modifications to the hood or canopy on your aquarium before you can fit the bulb(s). You need to have more space above your tank to allow the bulbs to be placed further away from the water, and you will need to cool the canopy by adding fans.

After all of this, it may still not be enough, especially with the metal halide bulbs. To be honest, this type of bulb is best fitted outside of a canopy, facing downwards. By putting it as high as possible above the tank, you are not restricting the light but are reducing the heat transfer. The more air there is between the source and the water, the better!

However, if you really want to make a difference to your aquarium, have a reef tank or heavily planted tank, you may want to look at this as an option. Care will need to be taken but the end result will justify the effort!