While I haven't had a lucid dream I've had several dreams where the level of light changes spontaneously. Always from day to night. For instance in one dream it was evening like the sun was starting to set and I went inside my house and my mom said "What are you doing out so late?" and I was like "Huh?" and then she said "It's one o' clock." and I look up at the clock and it's says it's one o' clock and now everything's dark outside and only the kitchen light is on. But way to beat the system anyhow stephent91.