Your body clock, turned into a plan.
A steady, well-timed circadian rhythm is linked to better sleep, daytime alertness, mood, and long-term metabolic health. The strongest thing that sets it is the blue signal: the light in the 440–495 nm band your body clock reads. Plenty of it by day, almost none by night. OIO's coach reads your own sleep and activity, works out where your clock sits, and turns a century of circadian science into a few things to do today. Here's the science it runs on, in plain terms.
Want the rigorous version? Read the Korrus white paper, What Circadian Rhythms Are.
A 24-hour rhythm you can't feel, but can read.
Deep in your brain, a cluster of neurons called the suprachiasmatic nucleus keeps a roughly 24-hour beat. It drives when you feel alert, when your temperature dips, and when melatonin, the hormone that opens the door to sleep, is released.
Left alone, that clock runs a little slow, closer to 24.2 hours. One thing resets it every day: light. Special cells in your eye, tuned to blue-cyan light around 490 nm, tell the clock what time it is. Get the timing wrong and the clock drifts, which is why late-night light pushes your sleep later and later.
Two forces decide when you sleep.
The classic model of sleep, from Alexander Borbély, has two parts. Process S, sleep pressure, builds the longer you're awake and drains while you sleep. Process C, the circadian signal, is your body clock actively keeping you alert through the day. You fall asleep easily when pressure is high and the clock's alerting signal has dropped away. When they're out of step, from late light or a shifting schedule, you lie awake tired.
Sleep pressure (Process S) climbs all day and falls overnight; the clock's alerting signal (Process C) peaks in the early evening and bottoms out before dawn. Sleep comes easily where the gap between them is widest. OIO's part is narrow and physical: keep the blue signal low at night, so a late dose of it isn't feeding the clock when it should be quieting down.
The actogram: your days, stacked.
Sleep scientists read rhythms with an actogram: every row is a day, laid out left to right, stacked downward so weeks of your pattern appear at a glance. Regular sleep makes a clean vertical band. Drift and irregularity show as ragged, wandering edges. It's how the coach turns your raw sleep and activity into a picture of your rhythm, and tracks it as you shift.
Each dark bar is a night's sleep, double-plotted across 48 hours so nights read continuously. This one starts late and irregular, gets coached about two hours earlier over a week, then holds steady at a new, regular time. It's a bounded phase advance to a target, not a drifting free-run — and the ragged early edges settling into a clean vertical band is regularity improving, the single biggest lever most people have.
The same light, at a different hour, does the opposite.
Light doesn't just switch the clock on and off; it nudges its timing, and the direction depends on when it lands. This is the phase-response curve. Bright light in the evening and early night delays your clock, pushing everything later. Bright light in the late night and morning advances it, pulling everything earlier. Around midday, your clock barely notices.
A schematic of the measured human light PRC (after Khalsa et al., 2003). Light before your body-clock low delays the clock; light in the morning after it advances the clock; the middle of the day barely responds. This is the lever the coach works with: front-load bright light after you wake, and clear the blue signal at night so evening light lands in the flat part of the curve. That's ZeroBlue's job — warm, lit rooms with almost nothing in the band the curve responds to.
How the coach turns this into your day.
Sleep and activity from Health Connect (Google Fit, Fitbit and more). Nothing leaves your phone.
Your own pattern, scored for regularity, timing, duration, amplitude and stability into one daily rhythm grade.
Estimates your melatonin timing and core-temperature low, so advice is aimed at your physiology, not the wall clock.
The two-process model and the phase-response curve become a plan: an anchor wake time, a morning bright-light window, a wind-down and a lights-out target.
Optional reminders at the moments that matter, and an optional auto-shift that eases your evening light earlier, day by day, toward your target.
OIO supports your circadian rhythm. It is not a medical device and does not diagnose or treat any sleep disorder. If sleep is a persistent problem, talk to a clinician.