Bunnies don't necessarily need to be provided with extra light and their sleeping habits are pretty arbitrary and sporadic anyway (they're crepuscular; which supposedly means most active at dusk and dawn but often translates to bouncing off the walls at 3 am, lol). As a general rule, they're fine with whatever lighting the human(s) in the house use for themselves. If they're in their own room rather than out in the house where lights are used for humans' activities, you could do either a 12/12 schedule or one that lines up with sunrise and sunset (which of course will vary depending on the time of year) if you wanted to provide them with artificial lighting. Really, though, they're no different from house cats or humans - nothing special needs to be done for rabbits
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Personally, my bunnies get whatever light suits us humans at any given time and they seem fine with it (even with us being somewhat nocturnal these days). They seem to determine day and night based on how much light is coming through the blinds for the 6'x6' window behind their condo and run.
I know the CFC bulbs (the new twisty looking ones that are energy efficient) provide the important type of natural light (UVB, I think it is) that doesn't make it through window glass - learned that while looking into what we'd need if we got a chameleon
. I also learned that if you're using them specifically for the UVB rays, they have to be replaced every 6 months because they'll stop giving off UVB even though they still give off the visible kind of light (UVA). As far as I know, there's no *need* to provide indoor rabbits with that sort of lighting... but it certainly couldn't hurt.