Aquarium Lighting: Do Fish Prefer the Light On or Off?

Ever wonder how fish respond to their tank lighting? Let’s take a look at how aquarium lighting impacts their health and comfort.

May 10, 2024By Dallin Darger
do fish prefer light on or light off

Lighting is a key component of any aquarium setup, but it’s not always clear why or how it affects your fish. Do they necessarily benefit from lighting, or is it something that should be used a little more sparingly?

Below, I’ll explore the psychological, biological, and atmospheric effects of aquarium lighting and help owners figure out what type of lighting conditions their fish prefer!

How Fish Respond to Lighting

red and blue fish in aquarium
Photo by Huy Phan on Unsplash

So, the main question first: Do fish prefer to have their light on? How do they respond to aquarium lighting, both in terms of physical health and psychological well-being? It may come as a surprise that, for the most part, fish don’t particularly care.

The large majority of fish species have minimal need for light. But, that doesn’t mean they mind getting more! Adding some extra lighting, so long as it’s not extreme or constant, rarely causes harm or discomfort.

If you want to err on the side of caution, a good trick is to try to mimic the conditions of the species’ natural habitat. For example, if your tank contains mainly tropical fish species such as angelfish or guppies, then a 12-hour lighting cycle is ideal. This lighting frequency most closely mirrors the lighting exposure of tropical waters.

In contrast, temperate fish like goldfish or zebrafish may benefit from varying lighting cycles over the year. This variation will help approximate the daylight cycle of temperate regions and add environmental enrichment.

Do Fish Need a Lot of Light?

several fish large aquarium
Wikimedia Commons

Figuring out the exact amount of light your fish need can be a tricky matter, as it tends to vary from species to species. Some presence of lighting is necessary to navigate underwater, but certain fish have higher visual sensitivity to light. Usually, you can deduce this based on the species’ natural environment. Fish that dwell under darker, murky waters are going to have different lighting preferences than those who swim in more brightly-lit coral reefs.

That said, there are some broad rules you can stick to for providing an appropriate amount of lighting to your tank:

  • Turn the aquarium light off during nighttime hours
  • Create an artificial, routine day-and-night cycle
  • Utilize colored LED lighting
  • Use timers and programmable lights to keep a regular schedule

Of course, you can always monitor your aquarium’s fish to see how they respond to the lighting setup. If you start noticing negative signs like sudden algae blooms, stressed fish, or unusual hiding behavior, you can then make adjustments to the lights.

Role of Aquarium Lighting

aquarium lighting
Photo by Jethro C

Now, if fish can typically do fine with minimal lighting, what’s the purpose of all these complex aquarium lighting setups? There are actually several benefits to artificially lighting your fish tank. The main advantage is simply that a little bit of extra light can help some species navigate more effectively.

Additionally, for exotic fish, using artificial lighting can assist in creating day-and-night cycles that don’t correspond to your time zone. And, of course, there’s the human benefit: More lighting helps us actually see the fish as they move around the tank!

Indirectly, fish can benefit enormously from a healthy aquarium environment created by added lighting. Aquatic plants, unlike fish, generally need a lot of light to thrive and grow, so lighting the tank fosters a more robust environment for your fish.

The important thing is to strike the right balance. You don’t want to have so little light that the aquarium’s plants don’t survive. But, you also don’t want to be the source of stressed out fish, create unwanted algae buildup, or cause health issues. To that end, maintaining a regular, artificial lighting cycle goes a long way toward striking that balance and producing the ideal ecosystem.

Artificial Day and Night Cycles

glowlight tetra dark tank
Wikimedia Commons

We’ve touched briefly on creating a routine pattern of daylight and nighttime hours for your aquarium, but let’s cover what that looks like in practice. Fortunately, it’s largely a straightforward process!

In most cases, the best way to approach this is by using a timer system for aquarium lighting. For tropical fish, for instance, you can set your ambient lighting to turn on and off in regular, 12-hour increments. It often works to even set this light cycle to correspond to the actual night and day cycle of where you’re living. But, this depends on which part of the world your fish come from, as they might follow a completely different biological clock.

When dealing with mainly temperate fish species, things can get a bit trickier. They might not thrive on a 12-hour daylight cycle, or maybe only follow it for certain parts of the year. In that case, I’d recommend researching the specific type of fish and seeing if there’s a consensus on the optimal lighting level.

Does Adding Sunlight Help?

yellow fish in aquarium
Photo by Nat Weerawong on Unsplash

It seems like common sense to introduce your aquarium to plentiful sunlight. After all, the only light source fish have in their natural habitat is sunlight. Does this hold up as a principle or is too much sunlight harmful for fish?

The answer is sort of a mix of both. Sunlight, in small doses, is almost never directly harmful to fish and actually provides a healthy mix of both natural and ambient lighting. On the other hand, too much sun causes problems. Common problems are heated tank water and unmanageable algae growth.

In fact, the dreaded algae blooms of some sunlight-exposed tanks make a lot of aquarium owners swear off the whole concept. Luckily, there’s plenty of middle ground between the two extremes. A few hours a day of moderate sunlight can help keep your plants and fish happy and healthy without mucking up the condition of the tank.

Dallin Darger
By Dallin Darger

Dallin is a passionate, seasoned pet owner and enthusiast. He has, over the course of 27 years, owned and loved a litany of breeds, from Labrador retrievers and calico cats to angelfish and neon tetras. Much of his free time is spent researching and learning everything he can about unfamiliar and exciting types of wildlife.