Is it wrong to leave a night-light on in the coop at night?

It is not "wrong." Perhaps unnecessary, but if it makes YOU feel better...

I will tell you that I have found that when I *must* have a light on in my coop (in a brooder, for instance), my rooster crows half the night.

 

I have a small nightlight in my coop I like having a tiny bit of visibility when I go out there at night w/out worrying about grabbing a flashlight. Plus, I've read that keeping a little light on inside the coop helps deter predators a bit.

 

There was an article this month in one of the poultry magazines that said it was a good idea for the babies. Going into a dark place was scary for them.

 

My chickens were afraid of the dark when I turned off their light. They got used to it in a couple of days. No, they don't need a nightlight, but I think if it makes YOU feel better, then no harm done. And since it's just a low light, it's not like you're burning up your power bill.

I'm not sure how well chickens can see in low light. Their night vision isn't very good.

Now that they are big girls and used to the dark, I find that they will stay up all night and pick on each other if I leave a light on (like in the winter when it's really cold and I turn on their red light for warmth).

 

There is a point at which the degree of brightness of the light will affect their day/night cycle. For birds, light cycles are everything. It affects not only physiological function (laying, molting... migration!), but psychological health as well (24 hr. light OR dark can cause feather plucking and other issues -- parrot rescue groups, anyone?). For me, that would be a huge consideration and I would do some quick research to find out more about it. I would think that 'laying pattern' is a good measure of affect.

Probably best to keep it under the brightness at which it affects laying. Don't know off the top of my head what that is.