Why are bars so dark? - Quora. It disguises how worn and dirty most bars are. Fewer windows mean less opportunity for after hours break-ins. it also disguises an empty bar from the casual passerby meaning that you will have to go inside to see if anyone is in the bar.
Window = potential charges pending. By law, you have to have all patrons out, and all booze put away, by 2 AM (where I live). Now, after a stressful day, most bars will allow the bartender a “shift drink” before leaving. This is very common; it is also technically illegal.