When To Use Blue Light In Aquariums? (The Precise Schedule)

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One of the questions I kept asking myself in the early days of fishkeeping was when exactly to use the blue light we are all familiar with.

I knew the color was meant to mimic moonlight and allow the fish to gradually transition from day to night. But I had no idea when to turn the blue light on and off.

In this article, I will walk you through this, and provide my personal aquarium lighting system to effectively automate the entire process.

This diagram illustrates the desired lighting cycle in fish tanks during the day.

When To Use Blue Light in Aquariums?

Aquarists use blue light in aquariums during evening and nighttime to help fish transition gradually from day to night. The maximum duration for blue light is 8-12 hours and should not be exceeded, even if it’s the primary light source.

Many aquarists perceive blue as a separate color whose function differs from the conventional white lights you typically see in an aquarium.

Therefore, they cannot help but wonder whether it follows a different set of rules. The answer to that question matters because it will determine how you use the blue light.

Consider the following:

1. The Accepted Period For Blue Light

The notion of using blue lighting for 8-12 hours doesn’t really make sense because blue is a transitional color. 

If you want to know when most people use the blue light, they wait until night falls. The average lighting schedule in an aquarium with a blue LED looks like this:

  • The blue light comes on between 6 pm to 11 pm (moonlight transition).
  • The blue light goes off between 11 pm to 6 am (sleep).
  • The orange light turns on between 6 am to 8 am (sunrise).
  • The orange color changes to white between 8 am to 6 pm (daylight)
  • The blue light comes on between 6 pm to 11 pm, and the cycle goes on.

Why would an aquarist select these particular times? The white light is more than adequate during the day.

You won’t get anything from a blue LED that a daylight bulb cannot provide during the day.

But in the early evening, the sun will begin to set.

Again, common sense will tell some aquarists to switch the white lights off, plunging the tank into darkness.

But that is a bad idea because the sudden absence of light can lead to shock and stress. Don’t forget that the sun doesn’t switch off in the wild. It gradually fades.

Keeping the blue light on at 5 pm but removing the white light allows the fish to gradually transition between daylight and nighttime.

The blue LED will lull the creatures into a state of relaxation, allowing them to sleep peacefully in the 8 or so hours of darkness that follow.

Switching the blue light on in the morning allows the fish to transition gradually to the daytime. White light can wake the fish, but again, you’re more likely to shock them.

The blue LED wakes them gently, allowing the fish to grow accustomed to the daylight before you switch the white light on.

Once the blue LED is on in the morning, you can keep it on until midnight. Naturally, your schedule will vary depending on when the sun sets and rises.

Ideally, you should turn the blue light on at 6:00 pm and off at about 11:00 pm.

2. The Maximum Duration For Blue Light

While aquarists routinely debate the merits of blue lights, especially in comparison to their white counterparts, they all agree that 8-12 hours is the maximum duration for a blue light.

This sounds like common sense, but it requires repeating because most people don’t apply this rule to traditional daylight bulbs.

They turn the lights on first thing in the morning and turn them off late in the evening before they sleep.

If they have a regular work schedule, they probably leave home at 8 am and sleep after 10 pm. In other words, their lights stay on from 8 am to 10 pm.

That sounds like a sensible schedule. But have you noticed that it forces the aquarium to tolerate 14 hours of light?

People follow this schedule instinctually. They expect the fish to mimic their resting patterns. That is a mistake. 

Stick to the 8-12hr rule. This is also true for blue lights. Most people keep them on for less than six hours.

But if you’re using the blue LED as your aquarium’s primary light, don’t exceed the 12-hour mark.

Can I Automate The Blue Light Schedule?

As you can probably imagine, providing your aquarium fish with an accurate lighting schedule can be daunting. And you are right to think so.

Changing the lighting colors several times a day every day is not a simple task. Fortunately, there are inexpensive ways to overcome this problem.

My life became much easier after I got the Hygger 24/7 Lighting Aquarium Light (link to Amazon). This system automates the previously mentioned cycle:

  • From 8 am to 6 pm, you will get white color.
  • From 6 pm to 10:50 pm, you will get the blue color, which imitates moonlight.
  • From 10:50 pm until 6 am the lights will be turned off.
  • From 6 am to 8 am, you will get an orange color, imitating the sunrise.
  • From 8 am to 6 pm, you will get the white color again, and so on.

Obviously, you can choose the exact model that fits your tank dimensions. And if you’re still hesitant, here’s an honest review of this lighting system:

Does The Type Of Fish Matter?

Why switch the blue light off at midnight? The color is soothing and relaxing. Why can’t you keep it on all night?

Because fish need sleep, just like humans. More importantly, they have a circadian rhythm.[1] Light affects the quality of their sleep.

Some fish won’t sleep if you keep the blue light on at night. Others will sleep, but they will exhibit signs of stress during the day because they can’t attain adequate rest.

They need regular periods of darkness. After all, the creatures don’t have eyelids. This is why newcomers don’t realize that fish need sleep.

They don’t understand that fish become unresponsive at night. They are still alert because they know that predators can strike at any moment.[2]

Nonetheless, this state of rest still counts as sleep, even though their eyes are open. Therefore, keeping the blue light on after midnight is out of the question.

But that raises a question. Does the type of fish matter? After all, you have humans that sleep with the lights on.

Fish have different needs where sleep is concerned. For instance, the Mexican cavefish sleeps for a whopping 1.5 hours a day.[3]

However, most people don’t keep Mexican cavefish in their aquariums.

There’s also the Rainbow Wrasse to consider. The fish burrows into the sand at night before falling asleep.

Technically, you won’t disturb this creature’s sleep by keeping the blue light on all night. The same could be said for the parrot fish (which sleeps under coral).[4]

But you can’t make your lighting schedule with these rare exceptions in mind.

You should assume that all your fish require 8 to 12 hours of light and an equal amount of darkness.

Nocturnal fish don’t change anything. You can keep the blue light on for a few hours at night to encourage nocturnal species to emerge.

But you must switch it off after a while. Nocturnal species don’t need light to feed and hunt at night.

Parrot fish usually use some form of shelter when they go to sleep.

What About Plant-Only Aquariums?

What if you have a plant-only aquarium? Can the blue light stay on? No, it can’t. Blue light benefits plants by driving photosynthesis.

However, it can also cause algae to grow. Therefore, you should stick to the 8-12-hour rule even in the absence of fish.

Why Should I Even Use Blue Lights?

The most important virtue of blue light is that it helps fish transition from day to night.

Some fish owners will also take advantage of the visual benefits that blue lights provide to enhance the colors of their fish. This is common practice with betta fish, for example.

This color is dimmer and warmer than the average daylight LED. Also, blue light penetrates deeper into the water, which is why some aquarists select the color over red. 

Blue is part of the sun’s visible wavelength, present in the 420nanometer range, and known for stimulating feeding and breeding.[5]

By using a daylight bulb, you’re inadvertently exposing the aquarium to blue light. Blue benefits both plants and aquatic animals, including aquarium shrimp.

You can invest in a lighting system that provides both blue and red to give the tank the best of both worlds.

Naturally, the intensity will determine the side effects you encounter. Aquarium lighting systems are versatile. You can make them as dim or bright as you want.

You can use blue light in both freshwater and saltwater tanks.


The blue light should be turned on between 18:00 to 23:00. This will allow your fish to transition from day to night gradually, which is what they also experience in the wild.

Turning off the blue light at 11 pm is critical, as leaving it on will prevent your fish from sleeping. Since fish have no eyelids, they need a dark environment to sleep in.

Also, leaving the blue light on for extended periods can cause algae overgrowth in your tank. Your plants will not benefit from this either.


  1. https://www.sleepfoundation.org/animals-and-sleep/how-do-fish-sleep
  2. https://oceanservice.noaa.gov/facts/fish-sleep.html
  3. https://www.nature.com/articles/d41586-018-01814-8
  4. https://thesleepdoctor.com/animal-sleep-habits/do-fish-sleep/
  5. https://www.futurepets.com/trivia/aquariums-lighting.htm