I saw a depressed kid and I gave him a lamp to lighten up his day.
Lighten Up
Explanation
Explain Bear
Listen up, buttercup. The 'joke' here is that the dude gave a lamp to a depressed kid to 'lighten' his day. Get it? Because lamps give light and 'lighten up' also means to become happier. It's wordplay, genius. Bet you still use training wheels.