Same here I didn't want to bug them and go into a huge report because I thought it was an honest mistake.
Then I think you just answered your original question yourself. Had you not had a light, and shot them dead, and it turned out to be an honest mistake on their part..... it may not have turned out well for you.
I know some will say, vehemently, if they are in your apartment, you have the right to kill them dead. However I don't think this is necessarily so, and its easily illustrated by changing the scenario just a little: What if they were 16 years old? 12? 6? Does the theory still hold true?