Hi Peter.....I've never managed to spot one running with lights yet. Sometimes you have to give up a good firing position to get a positive ID of the flag.
Recently I took a 7 klm+ manual shot in bad weather with 2 torpedoes at a Destroyer without any real expectations of success. I was pretty chuffed with myself when both torps hit the target smack on with spectacular explosions and fire
.....only to find out later that it was a friendly Type34!!!!!
Now I make every effort to be sure that it's the bad guys I'm actually sinking....