Reef Sources Guide - Lighting

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And God said, "Let there be light"; and there was light, and reef aquarists have argued over it ever since. If there is a single critical component in reef keeping, it is most likely lighting. You can short-change many things in an aquarium, but corals will die without sufficient light. Therefore, if you are going to cheap out, do it some place else.

T. MaximaTo decide what type and how much light you need, you need to decide what animals you are going to keep. Perhaps all you want is a couple of fish and some leather corals. Fine, 2-3 watts per gallon might be enough. But let's say it is an anemone, clam, or stony coral that has caught you eye. In this case, 5 watts per gallon would be a minimum. So, before you decide on lighting, or even a tank for that matter, figure out what animals you want to keep, and plan accordingly.

By the way, the watts-per-gallon measurement is arbitrary at best, but no better thumb rule has surfaced that I can adequately work with. So, regardless of tank size, it is my opinion that 5 watts per gallon is a minimum requirement for a reef that supports diverse life forms.

What kind of lights then? Aquarium lights come in three basic types: fluorescent, compact fluorescent, and metal halide. The choice is up to you. They all have pluses and minuses, as I will describe in the following paragraphs.


Fluorescent lights come in normal output (NO), high output (HO), very high output (VHO), and some manufacturers are referring to compact fluorescent as super high output (SHO). The SHOs, or compact fluorescent will be discussed later.

As for the NO/HO/VHO bulbs, imagine that the wattage for each model doubles with each higher standard. For example, a 24" NO bulb is ~20 watts, the HO version is ~40 watts, and the VHO version is ~80 watts. Coincidentally, the price of the bulbs and ballasts follow along accordingly. So what is the benefit of one over the other? You can get more wattage under a standard canopy using VHOs than with HO or NO. Keep in mind that all bulbs, regardless of style have to be periodically replaced due to color shift. With fluorescents, that time frame is generally 6-months, or about 1999-2000 hours of use.

Compact Fluorescent

Compact fluorescent are reasonably new to the aquarium hobby. They promise more light with less power consumption and greatly increased bulb life. These setups, at first blush, seem quite a bit pricier than their fluorescent brethren. But when compared over time, seem to fare better than the VHO setups. The bulbs only need replacing every 14 months, or 5000 hours, and rumors of reduced energy consumption add to the equation.

Metal Halide

Metal Halide is the gold standard for lighting for some aquarists. Why? Who knows? It could be because it was the first real bad-to-the-bone lighting system available to hobbyists. Maybe folks just like how the light is refracted from the surface of the water and causes the tank to shimmer (my reason). Maybe it could be that you can get a bunch of light from a single bulb (up to 400 watts). Regardless of what it is, folks like it.

Metal halide systems are costly, just like compact fluorescent, but may not compare favorably over time with other solutions. Bulb life is about 12 months, or 4000 hours, energy consumption is high, and they generate a lot of heat. But, from my point of view, the shimmer is worth it.


As a final note on lighting, quantity is not enough. You also must have the right color rendering for good animal health and reduced maintenance. Too much red and algae goes wild, as happens with aging bulbs of which color shifts toward the red spectrum. Not enough blue, and deep-water animals may suffer. Basically, the range to shoot for is between 5600° Kelvin and 20,000°K. Most aquarist will find that a 6500°K daylight bulb with Actinic 03 supplements will provide a pleasing display and provide much of what the animals need.

Let me repeat myself at the risk of sounding redundant. If you have got to cut corners to get you tank in under budget, don't skimp on the lighting.

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Copyright © 1999-2000, Scott Brown, except as otherwise noted. All rights reserved. This work may not be reproduced, in part, or in full, without the express written consent of the copyright holder.