I think that many years ago, there was a song in which the singer said, "You light up my life." That is, you brighten my life. "Brighten" my life could be interpreted as: a.. I was in darkness because I was lonely. When I met you, it was like turning on the lights. I am no longer lonely. b. I was in darkness because I was ignorant about life. When I met you, it was like turning on the lights. I have learned the truth about life from you.

These days you should use 'lit' in all of them except the 'a lamp can light a room' sentence which is fine but 'light up' is more common in this case. Lighted is correct but old fashioned at this point.

haha! lit! past tense conjugation is lit. (1) and (2) are both lit, past tense - bonfire lit up, I lit up the room (4) her fact lit up