How do blind people tell if it is night or day?

If you live north of the Artic circle and have endless nights in winter and endless daylight in summer, you wouldn't be using daylight to tell time anyway, so again this isn't a big deal for blind people. read more

Most people’s internal clocks naturally run slightly longer than 24 hours. Among the sighted, the clock is reset each day by signals from light-sensing cells in the eyes. But those who are totally blind lack this master reset mechanism. In theory, a blind person with a cycle of 24.5 hours would feel ready for sleep 30 minutes later each day. read more