How Long Should I Leave My Aquarium Light On?

It goes without saying that aquarium lighting is an important feature, often essential when it comes to the care of your fish. This, in general, is for three main reasons. One, it adds to the attractiveness of your aquarium set up, two; it is essential to the growth of live aquatic plants, and three, it allows you to see your fish in dim and dark conditions.

How long should I leave my aquarium light on – Aquarium lights are used for a number of reason. To grow aquatic plants, to view your aquarium and to fit in with your fishes natural living pattern. The average freshwater aquarium light should be on for 8-10 hours maximum. Saltwater aquariums need increased lighting and longer periods 9-11 hours a day.

Most fish keepers take great care over the choice of aquarium lighting that they use, and this is understandable. After all, you want the best for your beloved fish, and giving them the best setup you can provide this.

However, and you may be surprised to hear this, the type of lighting is not of the greatest importance. Rather, it is the length of time you have your aquarium lights on.

In general, 8 to 12 hours of light per day is recommended for your aquarium. However, this is just a general guideline and can alter dependent on different factors.

Below we will look at all these factors and help you answer the question ‘how long should I leave my aquarium lights on?’

How Much Light Is Needed?

This is the million dollar question, and the answer will vary dependent on the type of aquarium you are keeping. Important factors you will need to take into account are:

  • Are you growing live aquatic plants in your aquarium?
  • What species of fish are you keeping?
  • Does your aquarium get a good dose of ambient light?
  • Is algae a problem within your aquarium?
  • Does your lighting give off a lot of heat?

Live Aquatic Plant Aquariums

Aquatic plants, just like any other plants, thrive best in properly lit conditions. This is due to them, as I’m sure you know, using light to synthesize food from water and carbon dioxide.

A scientific process is known as photosynthesis. In turn, they then provide oxygen for your aquarium and clean up harmful waste.

Since light is a prerequisite to plant growth, it makes sense that it is advisable to provide as much light as possible to them. When it comes to your aquarium, you can do that by switching on your lights as the natural daylight fades.

Lights can be left on as long as you wish though you will need to take into account the needs of particular fish species.

Useful Tip: When adding new plants to your aquarium additional light time will help them root better and encourage vigorous growth.

Fish Lighting Requirements

Believe it or not, fish, in general, do not really care about, nor benefit from supplemental lighting in their aquariums. This is mainly because being kept in an aquarium with four glass sides gives them more access to light than their natural environment would.

To put it simply, with regards to fish, additional lighting is really all about what we like.

( Programable light timers)

There are, however, exceptions to this, such as Cichlids, Tetras, and Elephant Nose fish who prefer dimmer light and have been known to be adversely affected by bright light. It, therefore, is advisable to do some research on the fish species in your aquarium to see if they have any special lighting requirements.

For those fish who do not have special lighting needs the general rule of thumb for lighting would be 8 to 12 hours per day. Most of this, especially in the summer months, will come from natural lighting, but in winter you will need to turn your lighting on more.

Useful Tip: Do not leave aquarium lighting on overnight. Fish do need to rest and sleep and the majority, like us, do this in the dark.

Using a programmable timer can help control the amount of light your aquarium receives, even when you’re not at home or if you go on vacation. They are easy to set up, reliable and inexpensive to purchase.

We like the TOGOAL TE02 which is available at the best price from Amazon and comes with free next day delivery to most areas. 

Ambient Lighting Effects

The amount of ambient lighting your aquarium receives, as covered briefly above, will have a huge effect on how long you will need your supplemental lighting on.

For example, a bright sunny room will need less additional light than a dimly lit one, as will a room that is commonly artificially lit. Seasons also play a part in ambient lighting since in winter darkness sets in earlier than in summer.

Useful Tip: If your fish appear to be resting or sleeping far more than they are active, it is a sign they are not getting enough light. Switch on your aquarium lights if this appears to be the case, to ensure they get 8 to 12 hours of light per day.

Algae Issues

I think it goes without saying now, though I’m going to say it anyway, that getting enough light is important to your aquarium. However, it is also just as important that they do not get too much light. This is mainly due to excess light being a huge cause of algae overgrowth.  

( Incorrect amount of light can produce excessive algae growth)

Whilst excess algae growth is more commonly linked to natural sunlight and having your aquarium directly in the path of it, it can also be the result of too much supplemental light.

Either way, it is a nightmare to get rid of when it takes a hold of your aquarium, and not very attractive. If you do find that your aquarium is suffering from an algae bloom, you should reduce the time your supplemental lights are on.

There are a number of fish that can help you clean your aquarium by eating excessive algae. Read our article entitled ‘ Best Freshwater Aquarium Cleaning Fish and Snailsfor a complete guide to the best freshwater algae eaters.

Another really popular algae eater is the siamese algae eater which is sold in their thousands each year across the world and a great hardy freshwater fish that will eat a huge amount of algae. 

Useful Tip: Some algae in your aquarium is beneficial as it is a source of food for some species of fish.

Heat Omitting Lighting

It may not be your first thought but it should be taken into consideration that, not only does aquarium lighting produce light, but it also produces heat.

This means, that your choice of lighting has the potential to heat your aquarium and cause problems with your fish. This is especially true of smaller aquariums where the possible increase of temperature could be high.

The main lighting culprits of heating aquarium water are incandescent, VHO-fluorescent, and metal halide and you should monitor water temperature if you choose to use these. Lower heat output lighting includes normal fluorescent and LED.

Useful Tip: As well as producing less heat, LEDs also use 80% less electricity and may be better for growing plants.

LED Aquarium Lights

( Available in all sizes from Amazon)

LEDs emit light as exited subatomic particles pass through a semiconductor material i.e. electroluminescence. This requires relatively lower energy, producing a bright light that is both efficient and delivers on brightness for up to 50,000 hours. A diverse range of uses includes supplemental lighting or major lighting for aquatic tanks. (0.05-5W)

These have fast become the most popular way to light your aquarium. Long gone are the days of lighting your fish tank with dangerous red hot light bulbs are unreliable fluorescent tubes that where the starters constantly break. 

LED lights are cool, inexpensive, easy to fit and very reliable. They also are available in many color spectrums for both saltwater and freshwater plant growth. Making them the first choice for most aquarists. 

Starting at around $40 they are no longer only available to the elite aquarist who spends a fortune on their equipment.

We highly recommend the Koval 129 LED Light which has 5 spectrum settings making it perfect for freshwater or saltwater aquariums. 


It would be incredibly fair to say that in no way have we answered the question of how long to leave your aquarium lights on exactly! However, and to be fair again, there is no exact answer.

Rather, as with many aspects of fish keeping, the answer is based on a set of variables.

We have, however, given you all the variables you need to take into account with aquarium lighting, the tools if you like, to make your choices.

Simply, pick and choose the ones that are of importance to you and your aquarium, and you won’t go far wrong!

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