your body clock is set by light. bright, blue-rich light during the day keeps you alert and anchors your circadian rhythm. the same light in the evening suppresses melatonin and pushes sleep later.

screens are the brightest, bluest thing most of us look at after sunset. warming and dimming them as the real sun goes down removes that signal, so evenings wind down the way they're supposed to and eyes stop fighting a small daylight-colored lamp in a dark room.

circa does this automatically, from your actual sunrise and sunset. nothing to remember, nothing to schedule.