Reef Lighting and Coral Development: A Basic Guide

By: Henry Garcia

Hello, aquarium enthusiasts! Before we begin with the main content, let’s have a quick review of coral. Coral is made up of two parts: an algae known as zooxanthelle, which lives in the tissue of an animal known as a polyp. The zooxanthelle performs photosynthesis, which gives the polyp energy. The polyp eats zooplankton and produces waste, which aids in the growth of the zooxanthelle. The polyp also produces limestone, which provides a safe place for the zooxanthelle, and other creatures, to live. This symbiotic relationship helps form a reef. However, the beauty of the reef comes at a cost: coral is EXTREMELY sensitive, especially to things like temperature. Coral can only thrive in a certain temperature range: too cold, or too hot, and the entire system will begin to die. In the case of a reef grown in an aquarium, there are a lot of things to take into consideration. One of the issues that directly relates to the issue of temperature is lighting. Light, being energy, produces heat as its waste. There are four main types of lighting for aquariums: incandescent lighting, fluorescent lighting, metal halide lighting, and LED lighting. How each type of reef lighting affects coral development is precisely what is going to be discussed here.

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Aquarium lit by soft orange light. Stock image found at


Incandescent Light

Incandescent lighting has been around for a very long time. It is usually the most cost effective, and it is generally what is used to light up a room, and what comes in aquarium starter kits. However, incandescent lights tend to burn extremely hot. This occurs due to the basic mechanics of the incandescent light bulb. The way it works is that a metal (usually tungsten) is heated to a high enough temperature to where it produces light. That can spell disaster for coral reef development, due to the sensitivity to temperature. Incandescent lights also generally only light up the spot that they are directly facing. This does not bode well for the zooxanthelle that are not directly under the lights, and for the ones that are, the heat emitted by the lights may do irreparable harm. Basically, incandescent lights should be avoided.


Fluorescent Light

Fluorescent lighting is a much better choice than incandescent lighting. It not only produces better light, it also usually operates at a lower temperature, giving the aquarium enthusiast more control over the temperature of the entire tank. Fluorescent lights contain small amounts of mercury, which produces ultraviolet light when heated. While ultraviolet light is normally invisible to the naked eye, fluorescent bulbs have a coating called phosphor, which converts the ultraviolet light into a visible, bright light. More energy goes into heating the mercury, so not as much of

it is lost as heat. There are different kinds of fluorescent lights, which produce different kinds of effects on coral reefs. There is the standard fluorescent light bulb, or the Normal Output model, that is generally ill equipped for a reef setting. It does not emit enough light to be useful. The High Output model and the Very High Output model offer more light, making them perfect for larger tanks, but they also produce more heat. The Compact Fluorescent Light model is one that is worth looking into, because it has more brightness than the standard fluorescent model, and is much more energy efficient. The effect these lights have on coral reefs depends greatly on the model and the color. They can produce a fluorescent blue light or they can approach a regular incandescent bulb color. Depending on the desired effect, a combination of lights can be used to promote growth and enhance color.

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Aquarium lit by a bright, white light. Stock image found at

Metal Halide Light

Metal halide lights are a pretty interesting choice. These lights approach daylight much more efficiently than other light bulbs, and are thus much better for growing plants with. The way these lights operate is quite impressive. Within the bulb are several gases known as halogens, and mercury. The mercury is heated using a tungsten electrode, and it begins to emit a very bright light. This light is then tempered by the halogen gases. Due to the extreme brightness of metal halide lamps, they must be placed far above the tank in question. If the bulb becomes wet, it can shatter, leaking mercury into the tank. The lights also burn much hotter than fluorescent lights. Something to counteract the heat, such as a chiller, is necessary if using these lights. It is also generally recommended to use a combination of metal halide and fluorescent lighting. If used properly, metal halide lights can increase the health and beauty of any live plants and coral in the tank.


RN Purple Encrusting Galaxia

LED Light

The final option for lighting that will be discussed here is LED lighting.  This is what we run here on most of our ReefNation grow out tanks. LED lights produce much less heat than any other kinds of lights, and that is due to their mode of operation. LED light is produced electrons that are exchanged between two crystals. The crystals are grown, and then receive special treatment that causes them to become semiconductors. The exchange of electrons produces photons, which is what the human eye perceives as light. Because there is no actual electrode heating involved, LED lights produce very little heat. LED lights are a relatively new lighting method for aquariums, and more is being done with them every day. They can be much more versatile than other forms of lighting, and they contain no mercury.

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Water lit by multi-colored lights. Stock image found at

Lighting is arguably one of the most important aspects of keeping a reef aquarium. The kind of coral desired usually decides the kind of lighting used. Obviously, efficiency and longevity require more financial investment. What the aquarium enthusiast should look at when deciding what kind of lighting to use for their aquarium is partly efficacy and partly personal taste. Look at the kinds of coral you are using, and consider what kind of aesthetic effect you want. Bright white lights are generally best for photosynthesis, and certain colors can really bring out the beauty of the reefs. Hopefully, this article has shed some “light” on the issue at hand, and will significantly enhance your reef experience.



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