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Sunlight context

Morning light helps your body clock, but UV needs care.

daygauge shows your time in daylight from Apple Health and the places on your Timeline next to your sleep. It does not tell you how much UV is right for you.

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The question

Start with what your own data can show.

Sunlight touches sleep, mood, vitamin D, skin ageing and modern indoor life.

That makes it easy to overclaim. The useful angle is timing and context: when you got outdoor light and whether your sleep timing moved. UV and vitamin D need more care.

Quick answer

daygauge shows time in daylight from Apple Health, your sleep timing against your usual window, and the weather when location is on. It does not measure UV or vitamin D.

Questions answered

What this guide covers.

  • Does morning sunlight affect sleep?
  • How can you track outdoor light?
  • Can daygauge estimate vitamin D? No.
  • How does UV exposure differ from daylight timing?
  • What sunlight claims are best avoided?
In daygauge

How the app handles this.

Signal
daygauge shows time in daylight from Apple Health, your sleep timing against your usual window, and the weather when location is on.Daylight timing is not the same as UV exposure. daygauge does not measure UV dose, skin risk or vitamin D, and none of these change your Life Index.
Confidence
Missing readings lower confidence instead of creating false certainty.When a reading is not available, daygauge says so rather than filling the gap.
Weekly Review
Weekly Review shows what changed, what held and what to try next.Your first Weekly Review is free. Later reviews are part of Pro.
Illustrative example

What this can look like in the app.

Time in daylight: 22 minutes before 10:00 on 4 of 7 days; on those days you fell asleep 31 minutes earlier than your usual.

Example
Confidence

A pattern is only called proven after it repeats on your own paired days. Missing readings lower confidence.

Next move

Try one small change, log it in Quick Log, then compare your next readings.

Example 1

UV: daygauge does not measure UV. Midday sun in summer can burn, so cover up and use sunscreen.

Example 2

Vitamin D: daygauge does not measure or import vitamin D results. Ask a clinician if you are unsure of your levels.

Research

Further reading.

These studies describe groups of people. They help explain the topic, but they cannot tell you what will happen to you.

Research context only. daygauge does not diagnose, treat, prevent or predict disease risk. Personal medical concerns belong with a qualified clinician.

Limits

What daygauge does not do.

  • It does not diagnose, treat or prevent disease, or predict your risk of it.
  • It does not claim one habit caused a result. It shows the pattern, how confident it is and what else changed.
Read next

Related guides.

Circadian timing is about when you sleep, wake and get lightSleep midpoint can matter even when total sleep looks fineSauna is a useful experiment topic, not a universal prescription
On the App Store

Want to see your time in daylight next to your sleep?

daygauge is free to download. Pro is £8.99 a month or £49.99 a year.

Download on the App Store

Personal analytics, not medical advice