# Suddenly turning on the lights bad for fish?



## benealing (Jan 9, 2015)

I have come across many people stating that suddenly turning on the lights can "shock" a fish. While I agree that gentle changes in ambient light are ideal, is there any real scientific evidence to support that sudden lights on are detrimental to the fish? Has anyone actually killed a fish by flicking on the lights?

My parents blasted the lights on almost every morning when I was young and my biggest issues were intense anger and occasional disorientation :hihi:

Just a curiosity.

Ben


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## mistergreen (Dec 9, 2006)

benealing said:


> My parents blasted the lights on almost every morning when I was young and my biggest issues were intense anger and occasional disorientation :hihi:
> 
> Just a curiosity.
> 
> Ben


yup, that's all the effect it'll have on fish. If you don't want to startle them, use a dimming mechanism, usually with LED lighting.


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## lee739 (Oct 12, 2014)

I've heard people have had fish jump out in fright or crash into ornaments on sudden lights on...


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## garfieldnfish (Sep 25, 2010)

I usually turn the overhead light on and wait a little before turning on the tank lights. The overhead light in my fish room is pretty dim, so it does not startle the fish.


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## theatermusic87 (Jun 22, 2014)

I don't really have any issues with lights on, as the ambient light in the room is already pretty decent when the lights come on... HOWEVER

I was watching my tank the other nights when the lights went off, not only did it startle me a bit. But with no ambient light left, the tank was plunged into near total darkness (less a very dim green LED moonlight) and my fish, neons, rummynose, and white clouds, ALL lost the cohesion of their schools, flared their fins and seemed to swim around aimlessly for a few minutes before settling down.

TLDR; might not be just lights on, but sudden light changes that startle fish.


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## Solitarianknight (May 28, 2015)

My tanks get a good amount of filtered sunlight so they general don't mind me flipping the light suddenly. I did have a gold barb that slammed into the tank when I did one morning but gold barbs are like that.


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## iceburg (Jan 30, 2015)

One of my corries darts back and forth in what looks like a bit of a panicked search for a hiding spot when the light comes on suddenly. The other corries just move under the nearest plant until they start feeling comfortable again. Other fish don't seam to react other than the betta which just goes to his feeding corner and stares at me.


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## Italionstallion888 (Jun 29, 2013)

most of my fish are tucked away in their hideouts and I usually don't seem them for about 3-5min after the light comes on. Just like me, I think they take a few minutes to actually wake up. New fish that I add to the tank will get a bit confused, but after a week or so they are use to it. I also have my lights on individual timers, so the brighter lights don't come on until about mid cycle.


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## BeardedCrow81 (Mar 6, 2015)

Hmmm, in my experience, before the cool ramps and dims that are auto.

I'd come home, flick on the lights and wait at least 5 minutes for them to wake....


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## JJ09 (Sep 11, 2014)

One of my fish was at the surface when the light switched on and it went into spasms. It was actually spinning through the water and then died. I guess it was from the shock. I always do the lights gradually now- one tank has a dimmer option, the other one I try to remember to have room lights on before/off after the tank lights switch.


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## fisher1 (Jul 4, 2015)

Don't quote me maybe wrong (if it is please correct me  ) but many years back I read somewhere that apparently fish pupils take much longer to dilate/contract when sudden changes of light occurs and so when you suddenly turn on/off lights they are basically blind for up to 5mins. Can't remember where I read it and don't believe it as fact I haven't found anywhere else that stated that


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## hbosman (Oct 5, 2006)

My fish don't react to the lights coming on since it happens at 3:00 PM every day. The lights turn completely off at 10:00 PM. The fish generally are hidden in the plants a few minutes before the lights switch off as if, they are aware that it's time for them to do so. I think if you use a timer, the fish know to expect the sudden change. I would like to get an automatic dimmer for my LED lights but, since the fish aren't bothered, it hasn't been a priority. The dimming probably would be more for me than the fish. ;-)


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## Gplus (Apr 2, 2012)

The eyes in most fish cant react to sudden light changes very well. Some fish can take up to 30mins to totally acclimate to a lighting change. That's why you'll see some fish dart around the tank when there is a change in lighting. I had a rainbow fish injure herself pretty bad from turning ,y lights off a while back.... Its best to make sure the room is decently lit before your lights turn on and mostly dark before your lights turn off. Aside from that, you can get a lighting fixture that runs a sunrise and sunset function

Bump:


fisher1 said:


> Don't quote me maybe wrong (if it is please correct me  ) but many years back I read somewhere that apparently fish pupils take much longer to dilate/contract when sudden changes of light occurs and so when you suddenly turn on/off lights they are basically blind for up to 5mins. Can't remember where I read it and don't believe it as fact I haven't found anywhere else that stated that



+1 I've read the same thing


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