Aquarium Lighting – A general guide

October 9, 2009 — Marc

What kind of light you put on your aquarium depends greatly on what is in your aquarium. Some tanks require very bright light that calls for bulbs similar to what you see on car headlights or construction sites. Some tanks are very low light and can get buy with a single standard fluorescent bulb.

First some terminology.

Watts – The energy consumption of a bulb. You can also use it to give you an idea of how bright it is. Incandescent bulbs range from 15-100 watts and we all know which end is brighter.

Nanometers – Nanometers rating on a bulb can give you an idea of its burning color. The diagram below shows the visible light spectrum in nanometers.

Visible Color Spectrum in Nanometers (Nm)

Kelvin - This is the color temperature of a bulb. the lower the number the redder the light will be therefor a standard fluorescent cool-white bulb is usually rated at around 4100 K and a tungsten bulb you find in your home is around 2600K. This site has a great chart for comparison.

Color temperature comparison

Fluorescent – This is the least expensive, and least desirable option for your tank. Ranging from 15-40 watts, they do not cast much light. They should also be replaced fairly often as they wear quickly. Some people replace them every 6 months or more. Suited to a non-planted, small tropical tank of smaller than 30 gallons or as long as it is not too tall. Much larger/taller than that and you will have a hard time seeing the bottom of the tank!

Compact Fluorescent – With a similar range of color variant (3000-10000 K) as fluorescent the CF bulbs burn much brighter. Wattage for compact fluorescent ranges from 10-100 and run hotter than the cheaper counterpart. these bulbs most certainly will need ventilation as the heat is enough to warm up your tank a few degrees. Most come in a hood with built in fans.
These bulbs, being brighter, are more suited to low light planted tanks or low light coral reefs or fish only saltwater tanks.

High Output Fluorescent (HO) – These bulbs run on less wattage than the CF bulbs at 20-60 watts. They also burn brighter thanks to their compact form. the bulb is quite a bit thinner than a fluorescent bulb. The connector type is called a T5. The color range is a bit higher ranging from 6000-11000 K giving you much bluer light. This allows certain colors in the tank to really stand out. They are also a little more expensive but last longer than fluorescent and compact fluorescent.

Very HO Fluorescent (VHO) – These hot burning bulbs run at a higher wattage than the previous ones from 75-160 watts but deliver a much brighter/higher color light. The kelvin range for these bulbs range from 10000-20000 K. Due to their power requirements and the heat level they require a ballast to run. The bulbs last much longer but they run at a premium, as do the fixtures they come in.
Due to the high intensity of the bulbs, when lit in banks of 6 or more, you will have enough light for some high-light corals like SPS (small polyp stony) and clams.

Metal Halide – Metal Halide have for a long time, been the most sought after light by most reef-keeping saltwater aquarists. This light gives off light at such high intensity that the surface ripples on the water give a shimmer inside the tank. This simulates what one would see in the ocean. The Kelvin range is from 5000-20000K but run from 125-1000 watts. Power hungry lights are also among the more expensive and hot bulbs (sometimes costing as much as $200 each). Depending on your fish tank you may need 2 or maybe 3 of these. You can buy the fixtures in a pendant style where it hangs over your tank like a chandelier over a table, or you can buy a fixture that encloses 2 or 3 bulbs. These are ideal bulbs for a high light reef tank.

LED – The newest kid on the block, these fixtures are usually made up of many, many little LED emitters. We are seeing more and more of them coming out with full banks of these but many fixtures are a combination of LEDs and either metal halide, HO or VHO fluorescent. LED ‘bulbs’ do not generate heat, so they do not need a cooling system (unless coupled with another format of lighting). LED lights also come in a range of colors and the bulbs are controllable through an aquarium equipment controller (some lights are proprietary and require their own special controller).
The greatest features about LED, besides the fact that they have no heat, are thier brightness when grouped together, intensity of light, low cost and long life. Sounds like a dream come true! When grouped, they can offer similar lighting power to that of metal halide and with the intensity of metal halide. This means SHIMMER! They are incredibly cheap to produce and purchase, that is the LED components are, but for some reason they are still some of the most expensive units available for your aquarium. Go Figure. LEDs have a life span of approximately 50000 hours. Lets do the math. 50000 H = 2083 days = over 5 years. I’d say that’s a pretty good lifespan of a fixture. I am not sure if the manufacturers are making these fixtures with customer replaceable LED banks.

Actinic and Blue lights – Actinic lighting is a blue colored light that causes some colors in coral and fish to really POP out. The light appears at around 420 Nm in the visible color spectrum. Actinic lighting is beneficial to photosynthetic corals as well. See below for a comparison of some brown zoanthids without and with the actinic lighting.