I like having a nightlight of some sort in there....the birds have horrible night vision and I like to have something there so I can see them clearly, they can see me and I can see if anything is in there that should not be. Nothing bright or startling, just a soft ambient type lighting is all you and they could need.
I visit my coop during the night with no problems....as a matter of fact about to go check on the young ones out there after this post....I will go in and as soon as the door opens, speak to my 13lb rooster so he knows it is me coming in and I will go to the babies little brooder/coop inside and check on them and make any adjustments to fans, windows and etc before I lock the door till morning. It really does not bother them and I think my older birds enjoy it because they softly coo to me and my big boy brrrrruuuuuuuuurrrs to me and waits patiently for me to do my things in there and come to pat him before I leave.