How it works: you give the app your sleep goal, and then it coaches you by estimating current melanopic light exposure from the iPhone's camera. I validated this against an $1800 lab-grade light meter and was surprised to find it is absolutely close enough for these purposes. (Note: I'm NOT a physicist or circadian rhythm researcher, so I'm grateful for any feedback.)
If you feel like your sleep schedule could be more dependable or if you suffer from jet lag, you might enjoy this app!