It is also possible that your not entering as deep of a sleep, because your not as tired, or that you are more aware because your well rested in the afternoon.

Though generally yes, any thing that makes you uncomfortable keeps you from going into as deep of a sleep, which will help have a you lucid dream.

I have heard some people suggest things to make themself more uncomfortable when they sleep, using the same logic. Though I have to agree with you. Sleeping with a little light shining on you is probably better then sleeping on a board, or sleeping with clothes pins on your fingers.