General Consensus on Light Levels at Night

[Ianvaldius]

So obviously you want to leave the lights on for 10-12 hours a day on your fish tank and no more, but I haven't seen any general consensus on the difference in light levels between the day/night cycle and I'd love to hear everybody's opinions. I don't know if there have been any studies about it, but what do you guys think is an appropriate level of light during the night cycle? I have ambient light filtering into the rooms from the street lights outside for my two 10 gallons, 55 gallon, 2.5 gallon, and 5.5 gallon, but I have a 20 gallon in the bathroom and I'm torn between leaving the fairy lights on or off (they don't point directly at the tank). I know the stars and the moon light the water a little bit in their natural habitats, so I wonder if it's more important to have some level of light at night or for them to be in complete darkness. Do any of you cover your windows/tanks at night? It sounds a little overboard to me, but we all want what's best for the well-being of our fish.

 

[KevinZ]

Well, I dont really know that much but. i know that Fishes Dont Really Sleep.
They do "Rest / Nap" but they still Aware of their surroundings in case of any predatory. While in a Completed dark room. While we can't see at all. Fish still can still see their Environment somehow, I read this fact around the internet world, but idk if it's true or nah, i guess the best will be closest to their Natural Habitats ?

 

[Byron]

Light is crucial to fish health, something many aquarists fail to understand. And yes, fish absolutely must have a continuous period of several hours of total darkness. I will copy over an excerpt from an article I wrote for another site that should explain the importance; I can also copy the background data if asked. Before I do, I should point out that in their habitat waters, most (not all, but most) of our aquarium fish are forest fish, and the 10 or so hours of night are pitch black, there is no moon light or star light to speak of due to the forest canopy. Open rivers are obviously different, but here the fish (especially small species) live under floating vegetation which darkens their habitat so there is still little if any night light.

The Day/Night Cycle

Most animals have an internal body clock, called a circadian rhythm, which is modified by the light/dark cycle every 24 hours. This is the explanation for jet-lag in humans when time zones are crossed—our circadian rhythm is unbalanced and has to reset itself, which it does according to periods of light and dark. Our eyes play a primary role in this, but many of our body cells have some reaction to light levels. In fish this light sensitivity in their cells is very high.

Previously I mentioned that the rods and cones in the eye shift according to the changes in light. This process is also anticipated according to the time of day; the fish “expects” dawn and dusk, and the eyes will automatically begin to adjust accordingly. This is due to the circadian rhythm.

This is one reason why during each 24 hours a regular period of light/dark—ensuring there are several hours of complete darkness—is essential for the fish. In the tropics, day and night is equal for all 365 days a year, with approximately ten hours each of daylight and complete darkness, separated by fairly brief periods of dawn or dusk. The period of daylight produced by direct tank lighting can be shorter; and the period of total darkness can be somewhat shorter or longer—but there must be several hours of complete darkness in the aquarium. The dusk and dawn periods will appear to be stretched out, but that causes no problems for the fish. It is the bright overhead light that is the concern, along with having a suitable period of total darkness. And the "day" period when the tank lights are on should be one continuous period, not sporadic, and it should be the same every 24 hours or it will impact the circadian rhythm causing more stress.

 

[Retired Viking]

I have my tank lights on a timer. They come on at 10am and off at 9pm, I leave a dim room light on until 10pm so the fish get a sunset effect and in the morning light from the windows give them a sunrise.

 

[dmpfishlover]

I am so glad that I purchased a timer for my lights!! I don't have fish in my tank yet (it is still cycling... on Day 16), but when I do, I know now that they will get a consistent Day/Night cycle with the timer. This thread drove home for me, the importance of providing a consistent daylight cycle, and I know myself, and how forgetful I can be, that if I didn't have a timer for the lights, there would be NO WAY that the tank's day/night cycle could be consistent. Thank goodness for timers!

 

[Ianvaldius]

Light is crucial to fish health, something many aquarists fail to understand. And yes, fish absolutely must have a continuous period of several hours of total darkness. I will copy over an excerpt from an article I wrote for another site that should explain the importance; I can also copy the background data if asked. Before I do, I should point out that in their habitat waters, most (not all, but most) of our aquarium fish are forest fish, and the 10 or so hours of night are pitch black, there is no moon light or star light to speak of due to the forest canopy. Open rivers are obviously different, but here the fish (especially small species) live under floating vegetation which darkens their habitat so there is still little if any night light.

The Day/Night Cycle

Most animals have an internal body clock, called a circadian rhythm, which is modified by the light/dark cycle every 24 hours. This is the explanation for jet-lag in humans when time zones are crossed—our circadian rhythm is unbalanced and has to reset itself, which it does according to periods of light and dark. Our eyes play a primary role in this, but many of our body cells have some reaction to light levels. In fish this light sensitivity in their cells is very high.

Previously I mentioned that the rods and cones in the eye shift according to the changes in light. This process is also anticipated according to the time of day; the fish “expects” dawn and dusk, and the eyes will automatically begin to adjust accordingly. This is due to the circadian rhythm.

This is one reason why during each 24 hours a regular period of light/dark—ensuring there are several hours of complete darkness—is essential for the fish. In the tropics, day and night is equal for all 365 days a year, with approximately ten hours each of daylight and complete darkness, separated by fairly brief periods of dawn or dusk. The period of daylight produced by direct tank lighting can be shorter; and the period of total darkness can be somewhat shorter or longer—but there must be several hours of complete darkness in the aquarium. The dusk and dawn periods will appear to be stretched out, but that causes no problems for the fish. It is the bright overhead light that is the concern, along with having a suitable period of total darkness. And the "day" period when the tank lights are on should be one continuous period, not sporadic, and it should be the same every 24 hours or it will impact the circadian rhythm causing more stress.

This is all very helpful information! I will now try to turn the fairy lights off in the bathroom at night. Do you think the ambient street lights shining through the window would be an issue? What do you do personally? I make sure to turn all lights on at 10 and off at 10.

 

[Ianvaldius]

I am so glad that I purchased a timer for my lights!! I don't have fish in my tank yet (it is still cycling... on Day 16), but when I do, I know now that they will get a consistent Day/Night cycle with the timer. This thread drove home for me, the importance of providing a consistent daylight cycle, and I know myself, and how forgetful I can be, that if I didn't have a timer for the lights, there would be NO WAY that the tank's day/night cycle could be consistent. Thank goodness for timers!

I do really need to get a timer! My parents think I'm crazy because even when I'm staying with them down the road, I have to go back to the apartment and turn all the fish lights off!

 

[Byron]

This is all very helpful information! I will now try to turn the fairy lights off in the bathroom at night. Do you think the ambient street lights shining through the window would be an issue? What do you do personally? I make sure to turn all lights on at 10 and off at 10.

My fish tanks are in their own "bedroom," so it is easy to keep the window blinds permanently closed. Ambient daylight comes in during the day, and the tank lights come on and go off during this so I have no sudden light/dark problems. And at night the street lights cannot get through the closed blinds.

When I lived in the condo back before 2000, I did not know about all this and there was some "light" at night because I lived in the city. But if this is consistent, meaning all night and not bright light on/off as you would get from cars driving by, it should not be problematic.

I remember a botanical site mentioning how car lights shining through the indow at night are detected by aquarium plants in front of the window. Fish undoubtedly would have the same issue. But this illustrates how we don't usually even think of such things or their possible impacts.