Why do UFOs have lights?

Obviously, not all do. But the reason many or even most are seen in the night sky is that they have lights. They don’t seem to have any commonality. Some are steady, blinking, single or multiple, all the colors of the spectrum, etc.

Got to wondering about this. Seems like a silly question, but, seriously, assuming we’re talking about non-human vehicles, what would be the reason they have lights?