Choosing Aquarium Lights – Part 1 – Your Fish and the Color of the Light

This article is part of a three part series on aquarium lights; be sure to read the entire series!

Choosing the proper aquarium lights is very different from lighting your home. At home, you probably just buy a bulb that fits the fixture, put it in place, and go on your way. Your biggest choices are between overhead lighting and lamps, and traditional incandescent bulbs and compact fluorescents.

If you own an aquarium, however, lighting becomes a more important consideration. After all, if you keep pets in an aquarium, you are responsible for providing them with a healthy environment that closely mimics their natural habitat. To do this successfully, you need a few pieces of information.

What’s in your aquarium?

The first step in choosing lights is knowing what type of animals and plants you will be keeping in your tank. For the purposes of this article, we will be focusing on the care and keeping of fish.

o Freshwater fish: These are fish common to freshwater lakes and rivers, and are often referred to as “tropical fish.” Freshwater fish include goldfish, guppies, swordtails, and cichlids. Freshwater tanks may also include plants which grow in freshwater.

o Saltwater fish: These are fish and animals found in the ocean. They require the owner to prepare a saltwater solution that replicates ocean water as closely as possible. Popular saltwater fish include damsel fish, clown fish, triggerfish, pufferfish, sharks, and more. Other common “pets” in saltwater tanks include sea stars, anemones, sea cucumbers, and fan worms.

o Brackish water: Fish who live where freshwater and saltwater sources meet are said to live in brackish water. The water in a brackish tank is less salty than that used for saltwater fish. Mollys are among the most popular brackish water fish. Generally, lighting requirements for a brackish water aquarium are the same as for a freshwater aquarium.
o Reef tanks: These are saltwater tanks that include more than just fish, such as living coral, living rock, living sand, etc.

What color is your light?

We generally think of light as having no color. But think about what happens when light shines through a prism. The rainbow that results is because ordinary light has been broken up into its various color wavelengths. Without a prism, these different color wavelengths are quite difficult for the eye to distinguish, but they are there. The color of light is expressed according to the Kelvin scale, which also measures light temperature.

Here’s a quick rundown of the various lighting options.

o Lights rated at 5500K and below are typically incandescent bulbs in the red/yellow wavelength. These are not good choices for aquarium lights as they promote excessive algae growth. Natural sunlight is also to be avoided for this reason.

o 6500K lights are lights in the greenish/yellow wavelength. They are appropriate for freshwater tanks that are somewhat shallow (these lights are not good at penetrating deep water), as a supplement to saltwater or reef tanks using actinic light (more on that below), and for live plants.

o 10,000K lights produce a white light with a light bluish cast. This is a good choice for most tanks, including freshwater and saltwater tanks, and especially reefs tanks and tanks for deep water fish and plants. This type of light really shows off the beauty of your animals and plants to best advantage.

o 12,000K to 20,000K lights produce very intense white light with an increasingly bluish cast. These lights are best when the tank is deep, or you have fish that are natives of very deep water.

o Actinic light is not rated on the Kelvin scale. The numbers you will see on actinic bulbs are 420nm or 460nm, which are nanometer measurements. Think of actinic light as being on the very upper end of the blue spectrum nearing the ultraviolet range which we cannot completely see. The use of actinic light as aquarium lights is still undecided. They are most appropriate for reef tanks, and are often used in combination with other lights to provide light that more closely represents the full spectrum of natural light.

o Lunar or moon lights typically produce a blue light that does not provide much illumination, although white lunar lights reproduce the light of a full moon. These lights are usually LEDs and can be used in any type of tank, but are most useful when you need to simulate lunar cycles to breed fish.

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