Light green should be when you lie in bed, and dark green should be when you fall asleep. After accumulation, you can look at the monthly records and weekly highlights, so that you can know whether the sleep time this week is longer than last week.
In theory, Apple's own health software can detect sleep, and the mobile phone can monitor the surrounding sound environment, and then the mobile phone can analyze your sleep through data integration. If you wear smart devices, you can improve the accuracy of monitoring sleep.