For researchers
futurr light · research collaborations · October 2026
Apple Watch has estimated time in daylight for millions of wearers since 2023, from its ambient light sensor, every day, for years. As far as we can tell, no independent validation of that estimate has been published; if you know of one, we would be glad to hear about it. Either way, we would like to test it openly with researchers, and then make it easy and lawful to use in studies.
Why it matters
Personal light exposure is hard to measure at scale. Dedicated loggers are accurate but costly and worn for days; large cohorts such as UK Biobank have a week of wrist light per person. Meanwhile many study participants already wear a device that logs daylight continuously. Smartwatch-based estimates of time outdoors have already been used in research, for example in children's myopia cohorts. Whether the Apple Watch daylight record can be trusted, and for which questions, is an open and answerable question.
What we propose
1. Validate Apple Watch time in daylight
A study comparing Apple Watch time in daylight with reference light loggers at wrist and eye level (melanopic EDI, CIE S 026), across seasons, sleeves and settings. Co-designed with a light-measurement group, analysed openly, data released under CC-BY, results published wherever they land.
2. A study mode in futurr light
Participants who own an Apple Watch enter a study code, read the consent in the app, and choose what to share: daily time in daylight, sleep timing, duration and stages, optionally sunrise, sunset and cloud cover for their approximate location. Researchers receive clean exports with provenance: which device or app wrote each night, how overlapping sources were reconciled, time zones, and the algorithm version. Exports will follow the LightLogR conventions. EU hosting, a DPIA template and a processor agreement aligned with Dutch institutional requirements; transparent per-participant pricing, with free pilots for the first studies.
3. Open data
People who want to contribute will be able to donate de-identified daylight and sleep records to an open dataset under CC-BY, documented for reuse.
What already exists
- An iPhone and Apple Watch app that reads time in daylight and sleep from Apple Health and works on the device.
- Sleep handling designed for messy real data: samples from several sources merged without double counting, stages taken from one source per night (for example Apple Watch or an Oura ring), naps separated from main sleep.
- Within-person comparisons of sleep after brighter versus dimmer days, split at each person's own median day and reported only when robust to leaving out any two nights.
- An in-app library summarising peer-reviewed research on light, crediting every author, with DOIs checked and open-access copies linked.
How we work
Credit to the people who did the work, open methods, and claims no stronger than the evidence. futurr light is a wellness app; it does not diagnose or treat any condition.
Talk to us
If you study light, sleep or circadian rhythms and any of this is useful, or wrong, we would like to hear from you: research@futurr.health.