Comprehensive Lighting Guide

Why Lighting?

The simplest, most economic choice of lighting is sunlight. No tech aquarium folks believe there is no substitute. For many applications, aquarium lighting demands specific technology.

When you heat something, that something’s temperature goes up. At room temperature, this something will emit energy in the infrared (below red) range of light. However, hotter things emit light in the visible range (red to violet). Even hotter things may emit ultraviolet (above violet) light as well. The sun’s light is yellow. So, if you need something other than yellow light, then you need aquarium lighting.

What Lighting

Manufacturers standardize the spectrum of lamps using corrected olor temperature ratings (K) and color rendering indexes (CRIs). The K part tells you what color it looks like and the CRI part tells you how much it looks like that color.


Fluorescent lamps create large voltages across metal gases (fluors) in a coated tube. The electricity ionizes the gases and excites electrons in the gas. When these electrons relax, a little packet of light comes out called a photon. The coating on the tube is a material that absorbs UV light, and emits visible light. This coating largely determines the color of your lamp.

The phosphors degrade with use, and blue light intensity drops more quickly than red. So, lamps get darker and redder as time goes on. To maintain the blue and purple of a reef aquarium, lamps need to be changed at least twice a year; whereas the same aquarium may have red night lights that last a whole year.

There are only a few types of phosphors available. Many manufacturers use several coatings of different phosphors to achieve a balanced look. To achieve the most natural look, try to put as many different types of lamps in the canopy as possible. Most special bulbs accomplish the same thing as buying two daylight lamps and one cool white lamp (for example). The advantage to these special bulbs is that many people only have room for one lamp. There are exceptions to this rule and the number is growing, as some companies design aquarium lighting from the ground up instead of adapting existing technology to their needs.

The diameter of a lamp is very important. As the diameter increases, fabricating an effective reflector becomes increasingly difficult. The closer to a line source, where the diameter of the lamp is zero, the more effective a reflector will behave.

Balasts are designed for specific lamp types, and choosing a lamp also means limiting your choice of ballasts. The ballast determines the current and voltage to the lamp. A quality ballast will quickly pay for itself in reduced power bills and prolonged lamp life. Some ballasts have the option to attach a manual dimmer to the ballast. In conjunction with a timer, these ballasts can ramp light on and off to avoid the sudden firing of the lamp. Also, choosing a water proof ballast may come in handy.

Metal Halide

Metal halide lamps are essentially little fluorescent lamps on steroids. The metal halide gases are stored inside a coated quartz tube. This quartz is inside a glass shield to absorb UV light and provide a barrier if the quartz tube explodes. Instead of current flowing through the gas, the current actually arcs. This means higher temperatures and voltages. As such, metal halide lamps take a minute to start and then a few minutes to warm up. Basically, the ballast must start the arc and then vaporize everything inside the quartz sleeve. Probe start lamps have a small electrode inside the quartz tube to assist the firing the lamp. Pulse start lamps rely on the ballast to pulse the quartz tube to fire the lamp. Metal halide ballasts cannot be dimmed, unlike other types of lighting.

The color of the lamp is determined by the makeup of the halides and the phosphors coating the quartz tube. Pulse start lamps have a higher CRI, because the ballast is more gentle on the gases inside the quartz tube. Color ranges are nearly identical to fluorescent tubes; however, there are more options along the way. Metal halide lamps should last six months to a year. The blues in a metal halide lamp degrade very quickly. The most efficient metal halide lamps are near daylight. Because of this, many reefs rely on metal halide lamps for the daylight colors and fluorescent lamps for the purple and blue.


Light emitting diodes have come leaps and bounds recently. By 2008, new technology is scheduled to outperform all others (lumens per watt, lumens per dollar). There are still a handful of issues with LEDs, namely startup cost and color options. LEDs emit light in a very narrow range of colors, and the exact range of that color really depends on the batch and bin of the manufacturer. Also, initial costs of LED’s are quite high. Although, an individual LED is expected to have a lifetime of about ten years.

A handful of manufacturers sell LED lighting for the aquarium, but the nature of the wiring demands that an entire array of LEDs be replaced if a single burns out. And if you don’t replace the single array, then the others are not far behind. Thus, the benefits of LEDs are completely avoided. Basically, to save about 30% of the manufacturer’s costs, they ask you to replace $100 of LEDs when you really only need $5 replaced. A difficult fact to swallow when you’re already paying five to ten times as much as another technology, for the same amount of lighting.

One advantage of using LED lighting is the ability to program lighting intensity. The moon cycle, the seasons, cloud cover, sunrise, sunset, and anything else can be programmed into the lighting routine. This possibilities are huge with LEDs.


Lights are not 100% efficient. Therefore, lights create heat. This heat must be removed. If no efforts at ventilation are made, the the heat escapes via radiation. This may be adequate if the lamps are efficient and were designed to operate at elevated temperatures. Otherwise, ventilation may be required.

Simply drilling an array of holes above the lamps allows heat to escape through convection. This is adequate for most applications. However, often active ventilation is required. This involves placing a fan at either an input, an output, or both. If you are designing your own system, the ventilation that cools the lights can also be used to cool the aquarium water.

The Best Options

If you decide on the number of lumens you need, and then work backwards to how many lamps you need, then metal halide comes out on top. A metal halide lamp run by a pulse start electronic ballast puts out more lumens per watt and more lumens per dollar. However, in the next three months, the lamp’s luminosity decreases by 35%. In the same time, a T5 lamp’s luminosity will only decrease by about 6%. Also, consider that a quality reflector will direct about 80% of a metal halide lamps luminosity to the aquarium. A quality reflector for a T5 will direct over 90% of the light back. Notice, that the reflectivity of a reflector does not determine the amount of light reflected, but rather the probability an incident photon will be reflected. When you run the numbers again, T5 lighting comes out on top, by about 15%. Measurements with a light meter agree.

For a reef aquarium, most people want at least one metal halide. The real reason: metal halides look really cool. Reef aquariums usually have strong currents and surface waves. Metal halide lamps will make your reef sparkle, just like a real reef. Also, a single metal halide can provide a decent spectrum, whereas you really need at least two different color fluorescent lamps.

Compact fluorescent lamps provide a great alternative to T5 and metal halide lighting for smaller tanks. Reflectors must reflect light from more than one tube, which means that compact fluorescent lamps won’t perform as well as the corresponding straight tube lamps. However, bulb costs are lower, as a compact fluorescent lamp is essentially a longer lamp that is bent around.

By 2008, Atlanta Aquascapes plans on releasing a new LED lighting system for aquariums. This system will outperform all other lighting in terms of light output, light quality, and long term costs.

If you are looking for an economic option, then your local hardware store is the best place to start. Flat white paint has a reflectivity of about 95%, which is quite high. If you still have your high school geometry book, then you should be able to make your own reflector as well. Just find something relatively sturdy that you can cut with a razor. Watch out for silver materials when making a reflector. Some are excellent reflectors, and others are terrible.

Atlanta Aquascapes

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