Two · Inside you

Your body clock.

Nineteen windows in your day, computed from the light you actually get where you are — when to sit in the light, when the last coffee is, when to sleep, and when to take care.

Published chronobiologyTo the secondYour latitudeSources named

What we measure

Nineteen windows.

Each window is a number with the model it came from named. Four groups: the clock itself, sleep and alertness, sun and the seasons, travel and work — and one contested window, shown with both sides on the table.

Your solar daysunrise, sunset, day length, and how high the sun gets
Your clock’s phasetemperature low, melatonin onset, ideal bedtime, wake
Shift with lighthow far a bright-light session moves your clock, and when
Melanopic daylighthow much melatonin-active light today carries
Smart lightinga dawn-to-dark plan, and the warm-to-cool lamp ramp
Caffeine cutoffthe last real coffee, and how long it lingers
Perfect napthe post-lunch dip, and when to stop
Peak performancemorning focus, late-afternoon strength, the dip between
Danger hoursthe pre-dawn trough and the morning cardiac surge
Melatonin timingwhen, which way, and doses that work
UV & sunburntoday’s index, and minutes to one sunburn dose
Vitamin-D windowwhen the Sun is high enough, if at all today
Winter-blues windowthe morning light slot, graded to your latitude
Season trackerday length, and how fast it is changing
True noonwhy clock-noon is not sun-noon where you live
Golden hourevery twilight step, and the photo bands
Beat jet lagdays to adapt, which way, and the light plan
Shift-work strainforced hours against natural wake, scored
Moonlight & sleepcontested — both sides shown

The windows sit on the light, not on the clock

A sample day — not yours. Yours is computed from your latitude and the date, which is the whole point: the curve moves, and the windows move with it.

The curve is one day of daylight. Up at six, highest at one, gone by eight in the evening. Midnight to midnight along the bottom.
The three shaded blocks are three of the nineteen windows. Morning light 06:30 to 08:30, last coffee 13:30 to 15:30, dim the lights 20:00 to 22:00 — two hours each.
Dim begins exactly where the light ends. That is not a rule of thumb rounded to the hour. Move north, or move to December, and the curve changes shape and all nineteen windows move with it.

Free, no account

Your last safe coffee.

One of the nineteen, free and working. It depends on your body clock, not on the hour on the wall.

In development

Lived by, daily.

Body follows all nineteen windows through your day, wherever you wake up. Flow is a cycle tracker that states its uncertainty instead of faking a date. Both read the light your place actually gets, so the windows move when you do.

The apps →

BodyYour clock to the second: caffeine, light, jet lag, shifts.
FlowA cycle tracker that states its uncertainty.

Set to order

Reports and plans.

The body clock is printed to the case in front of it, not to a rack of fixed titles. Name the route and we set a jet-lag plan for it; name the ward or the crew and we set the rotation; name a latitude and we set the year in light. Each is computed for those exact people in that exact place, then typeset and delivered print-ready.

A jet-lag plan for one route and one departure
A shift rotation for a ward, a crew or a plant
A year in light for one latitude

A Year of Daylight: the length of the day through a year at one latitude, with the solstices, the equinoxes and the civil twilight band marked — **A year in light** — the third of the three, as it prints. The length of every day at one latitude, the twilight either side of it, and the solstices and equinoxes marked where they fall. The longest day, the shortest day and the swing between them are given as measured figures at the foot. Name a different latitude and the whole curve is recomputed for it.

Ask for a plan

Build with it

Nineteen windows, in your own code.

The full set of body-clock windows against the real sun at your caller’s latitude: sleep and wake, caffeine, light-shift, melatonin timing, alertness peaks, UV dose and vitamin D, jet lag and shift strain. Each returned as a number, with the published model it came from named alongside it.

Against real light — the sun at the caller’s own horizon, not a nominal day
To the second — instants, not buckets
Any place, any date — the same method everywhere
Named models — every window cites the chronobiology it implements
Plain JSON — small, flat, boring on purpose
No advice — you get the window, not our opinion of what to do in it
Nothing retained — health-adjacent input is answered and discarded
Stable shapes — fields are added, never renamed under you

Want it wired into a rota, a scheduler or an app you already run, or built into software of your own? Ask for that instead. And if you have looked at this and concluded it could not be done, bring it here and let us give it a second thought.

Tell us what you are building API, integrations and bespoke software →

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