First Tank Guide Tank Logo
First Tank Guide Home

Aquarium Lighting

Why Are There So Many Types of Lights, and What's the Difference?

(The First Tank Guide)

With the number of light bulbs, light tubes, light fixtures, light strips, and aquarium hoods available, aquarium lighting can be a confusing and frustrating subject. However, it does not have to be. This information should help you to make the right decision about your aquarium lights.

Aquarium Light Fixtures

The least expensive aquarium light fixtures are incandescent lights. These fixtures take regular screw-in type light bulbs. The bulbs are also relatively inexpensive. However, these bulbs need to be replaced much more often than other types of bulbs.

Unfortunately, incandescent light bulbs put out a lot of heat, making it more difficult to regulate the temperature in your fish tank. Also these lights use more power for the light they give off than most other aquarium lighting, so you will have a higher power bill using this type of fixture.

Many small, beginner aquarium kits (for ten or fifteen gallon (a bout 39-60 liter) fish tanks) come with incandescent light fixtures to keep the initial cost down. However, most aquarium owners quickly replace this type of light fixture with a fluorescent fixture. (So, you'll actually save money in electricity and equipment cost by buying the more expensive fluorescent light strip to begin with.)

The most common type of aquarium lighting is fluorescent. Fluorescent aquarium light fixtures are more expensive than incandescent fixtures, as are the bulbs. However, the bulbs use less power than incandescent bulbs, and last longer. In the long run, fluorescent lighting is actually cheaper than incandescent lighting.

Fluorescent lighting is available in many different grades or intensities, including Normal Output (or N.O., T8, T5, T12 or standard), High Output (or H.O. or T5-HO), Very High Output (or V.H.O.), and Power Compact.

For all fluorescent lighting, the amount of light put out is a function of the length of the bulb and the type of bulb, so if two bulbs are the same length and for the same fixture, they put out the same amount of light.

Another aquarium lighting option is metal halide lights, or M.H. lighting. Metal halide aquarium lighting requires special ballasts and special fixtures, and the lights use a lot of energy and produce a lot of heat. Be sure to completely read the instructions for your metal halide lighting and follow any safety recommendations before you set it up, due to the risk of fire or electrical problems if the lighting is set up improperly.

However, metal halide aquarium lights, if properly installed, can make an immense difference in the health of live plants or corals as well as the brightness of the tank. M.H. aquarium lighting is also the source of the shimmering or rippling effect seen on the bottom of fish tanks in large aquariums or in movies. Because of the fluctuation in the light emitted by metal halide lights over the course of the day, they should always be used in conjunction with a fluorescent light of some sort. To simplify this, many manufacturers make fixtures that have sockets for M.H. and V.H.O. or M.H. and power compact bulbs.

Aquarium Light Bulbs

There are many types of light bulbs available for whatever type of fixture you have.

Incandescent lights are available in a variety of colors to accent your aquarium, however there is no particular advantage to one variety over another. Even the incandescent lights designed to encourage plant growth do not provide as much benefit as even a regular N.O. fluorescent light.

Standard fluorescent lights are available in a variety of spectrums - different shades of white. Most of these bulbs look white when put on your tank, but if two are viewed side by side, you can tell the difference between the shades. These bulbs are engineered with different results in mind. Some are designed to penetrate further into the water, and therefore help with plant or coral growth in taller tanks. Others are designed to provide the best spectrum for plant growth in shorter tanks, while others are designed to bring out the natural colors of fish, and still others are designed to simulate the light about 30' under the surface of the ocean. These bulbs are usually sold under names to help you determine what they are supposed to be helpful for, and which is right for you. However, if you are not growing live plants or corals, then any nice white bulb should work very well.

For all fluorescent lights (N.O., V.H.O., and power compact) and metal halide lights, bulbs are available in spectrums identified by a "K" number which signifies a temperature on the Kelvin scale. The specific color of light emitted by these bulbs is the same as the light that would be emitted by a strand of Tungsten (a normal light bulb filament) if that strand were heated to that temperature in a vacuum. These lights simulate different lighting conditions depending on cloud cover, latitude, altitude, and other factors, allowing you to simulate the environment you wish to in your aquarium.

Light Penetration

Another concern with lighting your aquarium, is how well the light will penetrate to the bottom of the tank. In a short tank, this is not an issue. However as the height of the tank passes about 18", the water interferes with the light enough that, while the tank may appear well lit to the observer, the light that is reaching the bottom of the tank is no longer strong enough to help live plants (which should receive good lighting all the way to their bases) or photosynthetic live corals. Using high intensity N.O. fluorescent bulbs can give you another few inches of penetration, however, you provide good light penetration for more than 22" with N.O. fluorescent lights. Power compact or V.H.O. fluorescent lights penetrate further into your water column, typically providing effective lighting for tanks up to 30" high. Metal halide lights provide the best penetration and are beneficial in tanks over 30" high.

Bulb Life Expectancy

If you are only keeping fish in your aquariums, you only need to replace your light bulbs when they burn out, and this varies from bulb to bulb. If you are using N.O. fluorescent lights, you should replace the starter each time a bulb burns out, as often a burnt out bulb burns out the starter as well. If you are raising live plants or corals, you should replace your N.O. fluorescent lights every 5-7 months, because the intensity of the light begins to fade and it looses its helpfulness to the plants or animals that need it. You may not see this difference until you replace the bulb, but it certainly makes a difference to the plants or animals that depend on it! If you are doing this, remember to replace the starter(s) at least once a year. If you are using power compact or V.H.O. fluorescent lights, you should replace the bulbs about once a year, or whenever the bulb burns out. These bulbs are better able to maintain their spectrum over time, and do not degrade as fast as N.O. fluorescent bulbs. Metal halide bulbs should be replaced every 8-12 months. When changing M.H. or V.H.O. bulbs, remember to check the ballasts to see that they are working well and are not overheating or showing any other signs of wear. If there are signs of wear or other problems with the ballasts, they should be replaced at the same time.

Photoperiod or Lighting Duration

For most aquariums, you will want to have the lights on for 10-12 hours per day, however, if you are growing live plants or live corals, you may want to increase this light duration to 12-14 hours per day. I recommend that you get a timer to turn your lights on and off regularly. If the tank is in a room that is not completely dark, the time the lights are on should roughly coincide with the ambient light in the room, so the aquarium lights should be on during the day and off at night.

Overall Illumination

Another thing to consider is the overall intensity of the lighting you are providing in comparison to the tank volume and what you are illuminating. Again, if you are only keeping fish in your tank, then you probably only need to provide enough light so that you can see the fish and so that they can tell the difference between day and night. In fact, most fish will actually prefer a tank that is less brightly lit to one with very intense lighting. Contrary to that, if you have any photosynthetics in your tank, such as plants or, in marine (reef) tanks, corals or anemones, you will need to provide sufficient light for these plants or animals to photosynthesize. For plants, you will want to provide lighting that, in addition to being in the proper spectrum for your plants, provides at least two Watts per gallon of tank volume, but remember most plants will do better under four or five Watts per gallons. Reefs (marine tanks with corals or anemones) generally require even brighter lighting, usually in the range of five to eight Watts per gallon of tank capacity.

"Your site is the very best for information and thanks for all your help."
October 24, 2011
More Comments
"Oh, by the way, I LOVE YOUR SITE! It has been one of the ... most informative, yet easy to understand sites I have found. Great Job!"
October 9, 2003
More Comments