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Do Fish Like Light (For Health, Behavior and More)

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Fish live in many different conditions, including deep under the water with very little light. However, aquarium fish are exposed to all kinds of light, both natural and artificial. Understanding what type of lighting fish actually need, and what they like, can be one of the most confusing aspects of setting up a fish tank. 

Fish like light, but each species has its own light requirements. Most fish need around 12 hours of light each day to help them maintain their day and night cycle. The right amount and type of light will keep them happy and healthy. However, too much light can also cause problems. 

Throughout this article, I’ll explain each of these topics in more detail. I’ll also discuss some other related questions, like whether fish can live in the dark and if it’s a good idea to leave the lights on all the time. 

Do Fish Like Light in Their Tank?

Fish like a light in their tank, but the amount and type of light they need varies depending on the species. However, most fish need a significant amount of light. In general, most fish need 12-16 hours of light each day, with 12-8 hours of darkness. 

Why Fish Need Light

Most living creatures respond to circadian rhythms, which are bodily functions and processes that align with light and dark cycles. This cycle tells us when it’s time to go to sleep at night and when it’s time to wake up in the morning. 

Fish are no exception, as their bodies also align with the natural 24-hour cycles of day and night. 

Most aquarium fish need light to see when they are looking for food, swimming, and finding spaces to hide in. Their eyes function similarly to human eyes, except that they’re built for seeing underwater. 

Whereas our eyes have compressed lenses and a conical shape, fish lenses are spherical to help them focus underwater. 

However, some fish are better suited to see in low light waters, such as those found in deep waters or muddy rivers, or some thrive in bright light and clear waters, like many tropical species. These are some of the reasons that creating a similar environment can be helpful to the fish. 

I spoke with some of the experts at my local PetSmart about whether fish need lighting in the tank. They confirmed that lights are very beneficial to the aquarium setup, both for the fish and for the aesthetics of the tank itself. 

“What’s so cool now is that there are endless options for customization. Aquarium lighting not only helps the fish, but it’s another way that owners can really make the tank their own,” the clerk said. 

Benefits to Having Lights for a Fish Tank

In addition to the benefits to your fish, adding light to your aquarium also illuminates the tank so that you and your family can enjoy the views of your aquarium. If you have living plants in your tank, light is necessary to keep them healthy as well. 

Plants use light to produce energy and circulate carbon dioxide and oxygen, which can benefit the other life in the tank. 

Fish tanks with plants typically benefit from 12 hours of light each day, as do fish, tropical fish, and invertebrates. This is the amount of sunlight they would typically receive in their natural environments, so it’s ideal for their overall health and well-being. 

One of the biggest advantages is the aesthetic component that lighting adds to an aquarium. 

Lighting brings out the bright colors of the different kinds of fish in the tank. Often, brighter lights will even make certain pigments appear darker and stand out better.

Another advantage is that fish tank lighting keeps the temperature constant instead of putting the tank in front of a window or a place where it’ll get natural sunlight. While placing the tank in front of the sun’s rays may seem tempting, it can produce unpredictable results. 

Too much sunlight shining into a clear glass or acrylic fish tank creates the perfect environment for algae to grow and thrive. When the water consistently gets sun and the temperature levels off, cloudy days or periods where the sun is less intense than usual may cause the water temperature to drop. 

Similarly, if the tank suddenly starts getting more direct sunlight, it can raise the water temperature. 

Unexpected changes in the temperature can be disastrous for your fish, so it would be best to avoid this issue by choosing artificial lighting over direct exposure to natural sunlight.      

Are Fish OK in the Dark?

Fish are okay in the dark for periods of time, but most species need exposure to light and darkness to maintain their natural rhythms. Fish need darkness to rest, and they need light to help their bodies know when it’s time to be active. 

Each species may have its own specific needs and requirements when it comes to how much light and dark they need. However, if they don’t get exposed to any light, many fish may become stressed.   

Some fish are nocturnal and prefer the dark, while others may be more skittish and are most comfortable when they can hide under the cover of darkness. 

The most important thing is to try to have a regular schedule. It’s better for the fish if they know what to expect and can get into a routine. 

Can Fish Live Without Light?

Fish can live without light. They won’t die without light or be kept in a dark room. However, it’s not ideal to leave them with no light indefinitely. Without light, your fish won’t be able to sync up their natural rhythms, and you won’t be able to enjoy them if you can’t see them. 

Fish can also live without sunlight. 

Many people use artificial lights with their tanks, which is an easy and convenient way to take care of your fish and plants. In the wild, many fish species live in areas where there’s very little or no light at all. These species thrive, even in the darkness. 

However, it’s important to remember that these kinds of fish have adapted to their dark environments. Another species may not do as well in the same habitat. 

Though fish won’t die without light, it doesn’t mean they’ll be in their best condition. For example, a goldfish will start to lose its color if it’s kept in the dark. Some fish may get lethargic. Like all living things, fish do better when their environments are most closely matched with their natural habitat, including light and darkness. 

Can You Leave the Aquarium Light on 24/7?

It’s not a good idea to leave an aquarium’s light on 24 hours a day, seven days per week. When the tank is always in the light, it can stimulate algae growth. Having the lights on all the time also disrupts the internal clock for those living in the tank. 

Algae is a nuisance for anyone who owns an aquarium. It is a plant and needs both water and light to grow, and nutrients from the water as a food source. 

Light doesn’t cause algae to grow, but excessive light can make the conditions better for it. 

This is especially true for sunlight. It’s not a good idea to put your fish tank in direct sunlight for several reasons, but one of them is because it can contribute to algae growth. The ideal situation is to have your tank in a place where you can control the lighting. 

Artificial lights on the tank all the time can disrupt some of the natural, biological processes that fish and other living things do in alignment with the day and night cycle. 

Research has shown that light pollution and artificial light have had negative impacts on many living creatures. Behaviors like finding food, mating, and migration may all be impacted by artificial light. 

While these concerns aren’t necessarily associated with an in-home aquarium, they give some insight into the potential problems that animals can face when constantly exposed to an unnatural light source. 

Remember, the most important thing is to develop some sort of routine. It would be best to try to have the duration of light and dark time be the same every day so that the fish can adapt to this new rhythm. 

When To Turn Off the Aquarium Lights

Turning aquarium lights on and off can be a chore, and it’s easy to forget and leave them on all night or not turn them on at all. 

An easy solution is to use a timer for your fish tank lighting, or you can use a 12-hour schedule like turning the lights on at 9:00 PM and turning them off at 9:00 PM, to make it easier to remember. 

I personally like this BN-Link Plug-in Timer, found on, because it’s grounded for safety, and you can use it for anything that plugs in. It’s incredibly user-friendly with a simple design, which I also appreciate. 

I use them for Christmas tree lights as well. 

With a timer, you can set the lights to power on during the day and power off in the evening, similar to the natural timing of the sun. Or, you can turn them off when you go to bed and back on when you get up in the morning. 

Some aquarium lights even have settings to be programmed to change the “on” and “off” times seasonally or function like a sunrise and sunset. These are great options to provide your fish with an environment that’s more like the natural world. 

For example, this full-spectrum NICREW LED Light (available on comes in six different sizes and wattages and has an in-line timer to mimic a sunrise and sunset. Since the light has white, blue, and red lights, it provides varying wavelengths to promote plant health. 

I like it because the fish can wake up and fall asleep with a more gentle shift in lighting instead of being startled by a sudden change in the lights. 

Are LED Lights Bad for Fish?

LED lights aren’t bad for fish and are some of the most popular types to use in an aquarium setup. They’re good for use in fish tanks because they don’t give off as much heat as incandescent or other light bulbs. 

LED lights are an excellent option for home aquariums, as they’re very energy efficient and don’t use nearly as much power as some of the other types of bulbs. Another benefit is that they come in many different colors and styles to customize them however you like. 

They also work well for tanks with plants. 

Other Types of Aquarium Lighting

In addition to LED bulbs, many fish tanks are lit using incandescent or fluorescent bulbs. Incandescent bulbs are becoming much less popular over time because they tend to raise the water temperature. But there are more energy-efficient options available. 

Aquariums with more plants may need specialized lighting. 

People with brackish tanks may use UVB lights or infrared bulbs to provide lighting and warmth for plants and animals. 

Fluorescent bulbs are very common in aquariums because they’re versatile, easy to find, and relatively inexpensive compared to LED. Fluorescent may be normal output, high output, or very high output. 

Each output has a different wattage and may be used for different style tanks.

Metal halide produces light that’s much more natural in appearance and looks like the sunlight hitting the water. These lights are popular for reef tanks, and they create a beautiful look for any tank, but they’re typically the most expensive option. 

Unlike LED, metal halide also produces enough heat to potentially raise the water temperature, so you should always monitor carefully.

Final Thoughts

Fish are happiest and healthiest when their tank environment is close to their natural habitat. This includes having day and night cycles when the fish can have exposure to light and darkness. 

Nearly all living creatures respond to these light and dark cycles somehow, and fish are no different. 

Tank lighting also helps you to enjoy your aquarium setup, as you can see the fish swimming and interact with one another more easily. LED lights are very popular and energy-efficient options for aquarium lighting.  


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