Aquarium Lighting

Updated August 12, 2019
Author: Mike - FishLore Admin
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Aquarium lighting is an important aspect when keeping your aquarium and it is an often overlooked area that can sometimes be confusing for a beginner to aquariums. The confusion comes from the many available types of fish tank lighting.

The type of aquarium light you need for your fish tank really depends on what you plan on keeping in your aquarium. This article is a very general introduction into aquarium lighting and below we discuss the various types of lighting needs based on aquarium type.

Like we always say, we encourage you to research your livestock's lighting requirements for best results, but this article will give you a good intro and will give you a good idea of the type of lighting you should pursue.

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Aquarium Light Spectrum
Spectrum of visible light expressed in nanometers (nm).

Light Types

Regular Fluorescent Light

regular fluorescent aquarium light
These are the type of lights that come with most starter tanks and are very affordable. They typically range from 15 to 40 watts and have Kelvin ratings from 3,000° to 10,000°. Kelvin is the scale used to measure the color temperature. They are very cheap to run and replace. These are the often the stock lights that come with aquarium kits.

Compact Fluorescent Light Bulb

compact fluorescent aquarium light
These are a step up from the regular Fluorescent lights. They typically range from 10 to 100 watts and have Kelvin ratings from 5,000° to 10,000°. They offer really bright and intense light but they do put off some heat that may raise the tank water temperature. Running power compact lights will require special hoods and because of the heat produced, they often come with installed fans in the hood.

High Output (HO) or T5-HO Fluorescent Light

t5 fluorescent aquarium light
HO Fluorescent lights typically range from 20-60 watts and have Kelvin ratings from 6,000° to 11,000°. They are more expensive than regular Fluorescents and usually last longer. These lights require a T5 light fixture. T5-HO lights can be used to grow some of the most demanding SPS corals if placed in the middle to upper regions of the tank. I've been running reef tanks for years with T5-HO's with very good results. They provide lots of light and run much cooler than metal halides. Fixtures often have fans incorporated into them to keep the bulbs operating at optimum levels. Planted tank keepers may find that T5-HO's are good to use for their plated tanks as well.

Very High Output (VHO) Fluorescent Light

very high output fluorescent aquarium light
VHO Fluorescent lights typically range from 75-160 watts and have Kelvin ratings from 10,000° to 20,000°. These lights are very expensive and produce a lot of heat. They require a ballast and/or special fixture especially for VHO lights. They have fans incorporated into the lighting unit to help keep the lights and aquarium cool. Even though they come with fans you may need to equip your tank with an aquarium chiller to prevent your tank water from overheating. These are not as common as many of the other forms of aquarium lighting.

Metal Halide Light Bulb

metal halide aquarium light
Metal Halide lamps typically range from 175-1000 watts and have Kelvin ratings from 5,000° to 20,000°. This type of light is closest to the sun in terms of luminousity but they are very expensive to buy, operate and replace. They produce a lot of heat and usually must be fan cooled. Ballasts with fan units included are widely available. Metal Halides were often the preferred method of lighting a reef tank setup with anemones and corals that need higher intensity lighting but they are losing favor in place of T5-HO's and LEDs.

LED Light

LED  aquarium light
LED aquarium lights offer many advantages over the previously mentioned lights. Some of the advantages of LED lights over conventional Fluorescents and metal halides include:

Many of the light fixtures being sold now include moon lights which are LEDs. So we're starting to see them more often, but even though these LED aquarium lights are very promising we are probably still a few years away from using them as the primary light source on most home aquariums. Check out the ecotech radion LED lighting fixture which is getting really good reviews from hobbyists. I run these over my 120 gallon reef tank now and reviewed them for the magazine. Check out the Ecotech Radion Pro LED Review for more information.

Freshwater Lights - Fish Only

For a freshwater tank with no live plants you can get by with the low watt Fluorescent lights. These lights are typically between 18 and 40 watts and should last for a year or longer before they burn out. You mainly want light bulbs that will bring out the best colors in the fish you are keeping.

For fish only tanks there are lots of inexpensive LED lighting options these days.

Freshwater Aquarium Plant Lighting

Live plant keepers will need to upgrade their lighting system. The light type you need depends on several factors:

Typically, plant keepers try to provide anywhere from 2-5 watts per aquarium gallon. Research the plants you want to keep beforehand to determine if you can provide the light needed. T5-HO's can be a good option for plant keepers.

Saltwater Lights - Fish Only

Fish only saltwater tanks will work fine with regular Fluorescent bulbs. Try to get a "full spectrum" light for your tank or if you have a at least two bulbs a mix of 6,000 K and actinics can provide some nice colors.

While tanks with live rock can get by with regular Fluorescent full spectrum lights they will do better with Fluorescents and actinic lights (blue light). It really depends on how well you want the coralline algae to grow. Certain types of coralline algae seems to grow better with higher amounts of actinic lighting and low phosphate levels.

Saltwater Reef Lights

Saltwater reef tanks with corals, clams and other light needing organisms will need the high output, very high output Fluorescent or metal halide lamps. Certain corals, anemones and clams require very intense lighting levels that can only be provided with T5-HO, VHO and metal halide light sources. A general rule of thumb for reef tanks is between 4 and 10 watts per aquarium gallon. Many reefers have lighting systems incorporating metal halides and VHO Fluorescent tubes. Research the species you want to keep because light requirements can vary. Because of the amount of heat these light units can produce, you may need to get an aquarium chiller to keep your tank water temperature in an acceptable range. The expense of lighting a reef tank may be just as high or higher than the cost of the live rock or even the price of all the other equipment combined.

Aquarium Photo Period - How long do you leave the lights on?

How long should the fish tank lights stay on for? We get this question frequently. A good range to aim for would be anywhere from 6 to 12 hours. Remember that fish like and need to rest just like other animals. Fish only setups could range from 6 to 12 hours, reef tank setups and freshwater planted aquariums could range from 10 to 12 hour photo periods. Leaving the lights on for longer time periods could contribute to nuisance algae growth (just one of the factors with algae growth), higher tank temperatures and quicker tank water evaporation. Be consistent and if you can afford it, invest in a light timer.

Light Timer

You may also want to get a light timer like this one. A light timer can help make running an aquarium that much more enjoyable because it's one less thing you have to mess with. Most higher end fish tank hoods and fixtures have multiple power cords that are tied into the multiple light sockets within the hood. This allows you to setup your timer to turn on the various lights at different times.

For instance, a popular hood nowadays is the compact Fluorescent hood incorporating an actinic bulb, a full spectrum bulb and a moon light. You could set up the timer to turn on the actinic bulb to go on first and stay on for 12 hours, then have the full spectrum bulb come on an hour or so later and stay on for 10 hours. This could simulate dawn and dusk by having the actinic bulbs come on an hour early and stay on an hour later. Finally, you could have the moon lights turn on when the actinics turn off. Who knows, you may even start to see breeding behavior in certain species that may be more in tune with the light of the moon in this type of setup. Another side benefit of using a moon light is the super cool effect it creates in the aquarium when all the other lights in the room are off.


As you can see, the type of light you need really depends on they type of tank your running. Freshwater and Saltwater fish only tanks can usually get by with the regular Fluorescent lights whereas the freshwater plant keepers and saltwater reef tank keepers will need to invest in better light sources.

Please practice good aquarium electrical safety and be sure to use drip loops and gfci outlets!

For the reef tank keepers, below is a really interesting video on the light spectrum needed for corals and some of the popular lighting choices along with their spectrums. It is kind of long, but interesting information.

References :

Lighting Video

Aquarium Light Comments

From: Adrian Tong
I'm a beginner Saltwater aquarium hobbyist. I hope you could assist me regarding lighting. How long must the light be on? 24hrs? 12hrs? I'm having a 3" tank set up right now and I usually have the lights on only during the night for about 3-4 hrs. Is this wrong?
It depends on what you are planning on keeping in your saltwater tank. If you are keeping fish only or fish with shrimps or other lower light demanding species, then you will be ok just having the light on for 4 to 6 hours in the evening. They should get enough ambient light from the room during the day.

If you plan on keeping corals or want to grow grow coralline algae, or some other light demanding species then you will need to invest in some better lighting and plan on having the lights on for 8 to 12 hours per day. In the tropics the photo period is about 12 hours per day with the high intensity direct light happening only for 4 - 6 hours per day. The amount of direct light can be even less on cloudy, overcast days.

So, if you have a fish-only tank then you should be fine. Otherwise, plan on investing in a good light setup and plan on keeping the lights on for a longer period of time.

From: Kayla
Should I turn off the light before going to sleep? I have a freshwater tank with tetras and guppies.
Please read the article before asking questions, specifically the part on the photo period.

From: Ayan
I noticed you said something along the lines of "If you can afford it, invest in a timer." Fortunately timers have become very cheap nowadays. I don't believe in the digital timers because they are expensive and do the same job as a dialed timer. I went on vacation in December of 2008, and I went out to look for a timer. The fish hobbyists stores would sell them for $15 or more! I did a little bit more research and the exact same timers are $5 at your local Wal-Mart. I now leave the timer on because I'm not home in time to shed enough light in the tank. My ideal time is to keep it on for 7 hours (3-10 PM).
Great tip on the alternative place to buy a timer - thanks.

From: Landry
I just set up a top fin 20 gallon starter kit, in which I have some tetras and guppies. However I have noticed that the 18" florescent light bulb that it came with seems to be heating the water very quickly and I am concerned, also the tank at the fish store that I got my cardinal tetras from had a bulb that made the colors of the fish really bright almost like a black light effect. Is there a different type of bulb that I might be able to use that would help the temperature problem and/or make the colors of the aquarium brighter?
There are all sorts of lighting choices for Fluorescents. Actinics will cast a blueish light, full spectrums will usually be brighter. You don't mention an exact temp. you are getting... What is too high? Research your fish and determine the high range temps for them. Cardinal Tetras and Guppies should do ok in high 70's to very low 80's °F. Try increasing the water flow in the tank a bit and keeping the hood open if the temps get too high. You could also have a fan blowing over the top of the open hood to get an evaporative cooling effect. You'll have to do more freshwater top-offs though.

Related Aquarium Equipment Articles

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Freshwater Aquarium Light Forum
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