I'm sorry, something went wrong with the first post, and I have no idea how to delete it.
I was wondering if it's possible to have such luminous surrounding galaxy that it would be almost as bright at the night as at day.
However it seems it's not possible, without moons you always see nothing at night side, no matter how dense the galaxy neighborhood is.
Here is the extreme case.
se://v=990&n=Planet%20Frigid%20subjupit ... =1&f=2&e=0
The M87 Black hole's accretion disk is so bright that at close distance it's more bright than nearby star. However as you can see, it does not affect night side of a planet at all.
I wonder, is this being worked on? The night sides of planets in supermassive galaxies look very unrealistic right now...