What is a sun exposure tracker?

The phrase covers four genuinely different tools. Sun-position trackers (SunCalc, ShadeMap, Shadowmap) map where the sun and shadows fall — they answer 'will my garden get light at 3 PM', not 'am I burning'. Daylight trackers such as Apple Watch's Time in Daylight log how many minutes you spent outdoors. UV wearables and stickers measure the UV that landed on the sensor. UV dose apps combine the UV index forecast at your location with your skin type to work out how much of your safe exposure you have used. Only the last two track anything about your skin, and only the last one can tell you what is about to happen rather than what already did.

How do you measure sun exposure?

The scientific unit is the standard erythemal dose, or SED, where 1 SED equals 100 joules per square metre of erythemally-weighted UV. It is a dose, so it accumulates: intensity multiplied by time. A convenient rule of thumb is that one hour of full exposure at UV index 1 delivers about 0.9 SED, so an hour at UV 6 is around 5.4 SED. Sunburn starts at your minimal erythemal dose (MED), which is roughly 2 SED for very fair Type I skin and around 10 SED for Type VI. This is exactly the arithmetic behind a personal burn time.

What is the difference between tracking daylight and tracking UV?

Daylight tracking counts time outdoors. UV tracking counts dose. They diverge sharply because UV intensity varies by a factor of ten or more across a day, a season, and a latitude — the same hour outside can be harmless or a burn. For circadian and sleep benefits, daylight minutes are the right metric and more is generally better. For skin safety, UV dose is the right metric and there is a hard ceiling. Most people want both, which is why Apple's Time in Daylight and a UV forecast app are complements rather than substitutes.

Can an app track sun exposure automatically in the background?

Not reliably, and it is worth understanding why before trusting an app that claims to. A phone in your pocket or a bag cannot see the sky, so any app inferring exposure from phone sensors is guessing. iOS also rate-limits background location and refresh aggressively to protect battery, so continuous logging is not something a third-party app can do accurately. The approaches that genuinely measure dose are hardware — a UV wearable or a single-use sticker worn on exposed skin. The approach that genuinely helps you plan is a forecast: the UV index for your location combined with your skin type, telling you how long you have before you burn rather than reporting afterwards that you did.

Are UV stickers and UV wearables accurate?

They measure real UV rather than a modelled forecast, which is their genuine advantage, and for people who need hard evidence of dose — photosensitive patients, outdoor workers — they are worth considering. The limitations are practical: a sticker or wearable reports the UV that landed on the device, not on the rest of you, so a sensor on your wrist under a sleeve reads near zero while your face burns. Stickers are consumables and wearables are another thing to remember and charge. For most people the forecast approach costs nothing and answers the same question a few minutes earlier, which is when the answer is still actionable.

How much sun exposure per day is safe?

There is no single number, because the ceiling scales with your skin type. Sunburn begins at roughly 2 SED for Fitzpatrick Type I, 2.5 for Type II, 3 for Type III, 4.5 for Type IV, 6 for Type V, and around 10 for Type VI. In practice, that means a Type II person has about 33 minutes of unprotected midday exposure at UV 5 and a Type V person has around 80 minutes at the same UV. Below the burn threshold, UV still accumulates as long-term photoaging and skin cancer risk, so the goal is not to spend your full allowance every day — it is to know where the ceiling is and stay comfortably under it.

What is the best sun tracker app?

It depends which of the four jobs you mean, which is why roundups of 'best sun tracker apps' tend to compare tools that aren't substitutes for each other. For sun position and shade planning, SunCalc and ShadeMap are the strongest and are free on the web. For logged minutes outdoors, Apple Watch's built-in Time in Daylight is already on your wrist and nothing third-party beats it. For a measured dose, a wearable like sun-a-wear or a single-use UV sticker is the only option that reads real UV rather than a forecast. And for knowing how long you can stay out before you burn, you want a UV forecast app that applies your Fitzpatrick skin type — Sunwise on iPhone, iPad, and Apple Watch. If the goal is the opposite — a timed tanning session or enough sun for vitamin D — SunDose and Vitamin D: Sun & UV Tracker are built around those jobs. Pick by the question you're actually asking, not by the star rating.

Is there a sun exposure tracker that works without a wearable?

Yes, with one honest caveat about what 'tracking' can mean without hardware. Your phone can't measure UV — there is no UV sensor in an iPhone, and a phone in a pocket can't see the sky anyway — so any app claiming to passively measure your dose from phone sensors is estimating. What a phone can do well is forecast: pull the UV index for your GPS location, apply your skin type, and tell you the minutes of safe exposure remaining. That covers the decision you can still act on. For the historical half, Apple Watch's Time in Daylight logs your minutes outdoors into the Health app with no extra app at all. Between them you get a ceiling and a log without buying a sensor.

Does Sunwise track my sun exposure?

Sunwise is a UV forecast app rather than a passive exposure logger — it does not run in the background recording where you have been, and it does not write to Apple Health. What it does is the forward-looking half of the problem: it takes the UV index for your GPS location from Apple WeatherKit, applies your Fitzpatrick skin type, and shows how many minutes of safe exposure remain at the current UV, updating as the UV changes through the day. For logged daylight minutes, pair it with Apple Watch's built-in Time in Daylight in the Health app. The two answer different questions and neither replaces the other.

Sun Exposure Tracker: How to Actually Track UV Dose, Daylight Time, and Burn Risk

“Sun exposure tracker” is one search phrase covering four completely different tools — shadow maps, daylight-minute logs, UV wearables, and UV dose forecasts. They measure different things, and picking the wrong one is why people end up with a tracker that never warns them about anything. This guide explains what each approach actually measures, introduces the unit sun exposure is genuinely counted in, and shows how to estimate the UV dose you absorbed today — and how much your skin can take before it burns.

By Sunwise · Published August 18, 2026 · Updated October 7, 2026

Four things people mean by “sun exposure tracker”

Search results for this phrase mix sun-position calculators with health wearables and UV forecast apps, which is confusing because they answer entirely unrelated questions. Here's what each category is genuinely for.

Approach	What it measures	Good for	Blind spot
Sun position & shade mapsSunCalc, ShadeMap, Shadowmap, SunEarthTools	Where the sun sits and where shadows fall, for any time and place	Planning a garden, choosing an apartment, photography golden hour, working out whether a patio is shaded at 2 PM.	Nothing about UV intensity or your skin. A fully sunlit spot in December and in June look identical on the map.
Daylight-time trackingApple Watch Time in Daylight (Health app), Series 6 and later	Minutes spent in daylight, via the ambient light sensor	Circadian rhythm, sleep quality, mood, and children's myopia risk — all of which respond to time outdoors regardless of UV.	Counts minutes, not intensity. Twenty minutes at UV 2 and twenty at UV 10 log identically, so it can't flag burn risk.
UV wearables & stickerssun-a-wear, SpotMyUV and similar UV-reactive patches	Actual UV landing on the sensor or patch	Hard evidence of real dose — useful for photosensitive patients, outdoor workers, and anyone who distrusts a forecast.	Reports the device's exposure, not yours. A wrist sensor under a sleeve reads near zero while your face burns. Consumable or extra hardware.
UV dose forecast + burn timeSunwise and other Fitzpatrick-aware UV forecast apps	UV index at your GPS location, converted into remaining safe minutes for your skin type	Deciding what to do next — the only approach that answers the question before the damage rather than after it.	It's a forecast, not a measurement, and it can't know you spent the last hour under an umbrella. You supply the judgment.

The split that matters: the first two categories track where you were and for how long. The last two track what reached your skin. Only the last one tells you something while you can still act on it.

Which sun exposure tracker should you actually use?

Narrowing from categories to the specific tools people land on. The honest answer for most people is two of these rather than one — something that logs where you were, and something that tells you how much your skin can still take — because no single tool in the list does both well.

Tool	Type	What it measures	Skin-aware	Where it stops
sun-a-wear	Wearable UV sensor	Real UV landing on the device, with live alerts. No battery or charging.	Partly — alerts can be set against your sensitivity	Measures the sensor, not you. A tag on a bag reads differently from your face, and it reports dose as it happens rather than before.
SunCalc / SunEarthTools	Sun-position calculator	Where the sun sits and how shadows fall for any date, time, and place.	No	No UV, no skin, no dose. Superb for planning a garden or a photo; silent on whether you are about to burn.
ShadeMap / Shadowmap	Shadow simulation map	Building, tree, and terrain shadows across a whole city, hour by hour.	No	Answers 'will this bench be shaded at 2 PM', which is genuinely useful — but a sunlit square in December and in June look identical on the map.
Apple Watch Time in Daylight	Daylight-minute log (built in)	Minutes spent in daylight via the ambient light sensor, stored in Health.	No	Counts duration, not intensity. Twenty minutes at UV 2 and twenty at UV 10 log identically, so it can never flag burn risk.
Sun Tracker: UV Index & Tan	UV index + tan-session app	Real-time UV index, a morning forecast notification, and logged tan sessions.	Limited — tan-session guidance, not a burn time	The UV number is the same for everyone in your area, so 'how long have I got' still depends on you knowing your own tolerance.
SpotMyUV and similar stickers	Single-use UV patch	Whether the sunscreen over the patch has worn off, by colour change.	No	Consumable, and it reports the patch's exposure rather than your ears, nose, or the backs of your hands.
Vitamin D: Sun & UV Tracker	Vitamin D + UV tracking app	Estimated vitamin D from sunlight, tuned to your skin and location, with UV alerts and Apple Watch tracking.	Yes — tuned to your skin (the model isn't stated)	Built to get you more sun for vitamin D. The question it answers is 'have I had enough', not 'how long before I burn'.
SunDose: Tanning & UV Tracker	UV + tanning-session tracker	Real-time UV for your saved locations and a tanning timer personalized to skin type and SPF, with widgets and a Live Activity.	Yes — skin type and SPF shape the session timer	Tracks a tanning session you start deliberately. Great for a planned hour on a lounger; silent about the walk you didn't log.
Sunwise	UV dose forecast + burn time	UV index at your GPS location converted into remaining safe minutes for your skin.	Yes — full Fitzpatrick I–VI	A forecast, not a log. It assumes open sky, doesn't write to Apple Health, and can't know you spent the last hour under a tree.

Worth saying plainly: Sunwise is in that table and it is not a tracker in the logging sense. It does not run in the background, does not record where you have been, and does not write to Apple Health — a page about tracking would be dishonest to imply otherwise. What it does is the half none of the logging tools can do, which is tell you the number before the exposure rather than after. For the app-by-app comparison of the UV forecast side specifically, see the best UV index apps for iPhone roundup.

Apple Watch Time in Daylight — what it does and doesn't do

Apple Watch Series 6 and later record Time in Daylight using the ambient light sensor, and store it in the Health app alongside steps and heart rate. It is the closest thing to a built-in sun exposure tracker on iOS, and it is genuinely valuable: time outdoors drives circadian rhythm, sleep quality, and mood, and the metric was introduced partly because daylight exposure in childhood is protective against myopia.

What it cannot do is tell you about your skin. Time in Daylight counts minutes and treats them all as equal. Twenty minutes on a grey January morning at UV 1 and twenty minutes at the equator at UV 11 both log as twenty minutes, even though the second delivers roughly eleven times the dose. There is no skin-type input and no ceiling — the metric is framed as something to get more of, which is right for circadian health and exactly backwards for sunburn.

The two metrics are complements, not substitutes. Time in Daylight is a target you want to hit. UV dose is a ceiling you want to stay under. On a UV 2 winter afternoon you can maximise both at once; on a UV 10 July noon they pull in opposite directions, and the ceiling wins.

The unit sun exposure is actually measured in

Sun exposure is a dose — intensity multiplied by time — and the standard unit is the standard erythemal dose (SED), where 1 SED equals 100 joules per square metre of erythemally-weighted UV. Erythemally-weighted means the measurement is adjusted for how strongly each wavelength actually reddens human skin, so a SED is a dose of the UV that matters rather than of UV in general.

The useful thing is that the UV index converts into SED cleanly. A UV index of 1 corresponds to 25 milliwatts per square metre of erythemal irradiance, which works out to a simple rule:

One hour of full exposure at UV index 1 ≈ 0.9 SED. So an hour at UV 6 is about 5.4 SED, and half an hour at UV 8 is about 3.6 SED. Multiply the UV index by the hours spent at it, then by 0.9.

The other half of the equation is your minimal erythemal dose (MED) — the dose at which your skin starts to redden. This is what the Fitzpatrick scale is really describing. Cross your MED and you have a sunburn, whether or not you felt it happening.

How much sun exposure each skin type can take

Approximate burn thresholds in SED by Fitzpatrick type, with the unprotected exposure time that corresponds to at two common UV levels. If you don't know your type, take the Fitzpatrick skin type quiz first.

Type	Skin description	Burn threshold	Time at UV 5	Time at UV 8
I	Very fair, always burns, never tans	~2 SED	~27 min	~17 min
II	Fair, burns easily, tans minimally	~2.5 SED	~33 min	~21 min
III	Medium, sometimes burns, tans gradually	~3 SED	~40 min	~25 min
IV	Olive, rarely burns, tans easily	~4.5 SED	~60 min	~38 min
V	Brown, very rarely burns, tans darkly	~6 SED	~80 min	~50 min
VI	Very dark, almost never burns	~10 SED	~133 min	~83 min

These are unprotected times for bare skin in open sun, derived from the SED arithmetic above rather than measured on you specifically — individual MED varies, and a recent tan, a photosensitizing medication, or altitude will shift it. Treat them as a planning baseline, not a guarantee.

Estimating the dose you actually absorbed today

You can do this on the back of an envelope with the hourly UV curve from any UV forecast app. Worked example for a fair-skinned (Type II, ~2.5 SED) person on a summer Saturday:

1.List the hours you were outside, with the UV for each. Say 9–10 AM at UV 3, then 12–1 PM at UV 8, then 5–6 PM at UV 2. Don't average them — UV varies too much across a day for an average to mean anything.
2.Convert each block to SED. At 0.9 SED per UV-hour: the morning is 2.7 SED, the midday hour is 7.2 SED, the evening is 1.8 SED. Raw total: 11.7 SED — more than four times a Type II burn threshold.
3.Discount for what you were wearing and standing under. Say the midday hour was under a café awning (roughly a quarter of the open-sky dose, so 1.8 SED) and the morning and evening were in a t-shirt with well-applied SPF 30 on exposed skin. Forearms and face end up around 2.2 SED — just under the line. Covered shoulders got almost nothing.
4.Compare against your MED, per body area. This is the step people skip. Sunburn is local — your dose isn't one number for your whole body, which is why the back of the neck and the tops of the feet burn while everything else is fine.

Two things fall out of that example. First, the raw numbers are brutal — an unshaded midday hour at UV 8 alone is nearly three times a Type II burn threshold, which is why “I was only out for an hour” is such a common preface to a sunburn. Second, doing this arithmetic after the fact is useless. The value is in running it forwards, which is what a burn time is.

Why forecasting beats logging

A tracker that tells you at 6 PM that you absorbed 11 SED has told you something you already know, because your shoulders are pink. Sunburn also lags — the redness peaks 12 to 24 hours after the exposure that caused it — so even a perfectly accurate real-time logger is reporting damage that is already committed and irreversible.

The version of this that changes behaviour runs in the other direction: take the forecast UV for your location, apply your skin's threshold, and report the minutes remaining. That is a number you can act on — it turns “UV is high today” into “you have 21 minutes,” which is a decision rather than a mood.

It is worth being clear about the trade-off. A forecast can't know that you spent the last half hour under a tree, so it is deliberately conservative — it assumes open sky. A wearable sensor knows exactly what landed on it but nothing about the rest of you, and reports it too late to change the outcome. For most people the forecast is the more useful error to make.

A practical sun exposure routine

Combining the tools rather than picking one gets you the whole picture:

•Use Time in Daylight as a floor. Aim to hit a daily minimum of outdoor time for sleep and mood. On low-UV days there is no conflict at all — get as much as you like.
•Use a burn time as a ceiling. Check the remaining safe minutes before a long outdoor block, and plan to move into shade at roughly 60–70% of it rather than at zero.
•Use the hourly curve to move the block. Shifting a run from noon to 5 PM can cut the dose by three quarters for the same amount of time outside — by far the highest-leverage change available, and it costs nothing.
•Track per body area, informally. Note what was covered. The dose that burns you is the dose on your most-exposed patch of skin, not your average.

For the sunscreen half of this — how long a coat actually lasts and why reapplying doesn't reset the dose you've already taken — see the guide to when to reapply sunscreen. If your goal is to accumulate a useful dose rather than avoid one, the vitamin D and the UV index guide covers the window where UVB is strong enough to matter. And for what each UV level means before you start counting doses, see the UV index guide.

FAQ: tracking sun exposure

What is a sun exposure tracker?: The phrase covers four genuinely different tools. Sun-position trackers (SunCalc, ShadeMap, Shadowmap) map where the sun and shadows fall — they answer 'will my garden get light at 3 PM', not 'am I burning'. Daylight trackers such as Apple Watch's Time in Daylight log how many minutes you spent outdoors. UV wearables and stickers measure the UV that landed on the sensor. UV dose apps combine the UV index forecast at your location with your skin type to work out how much of your safe exposure you have used. Only the last two track anything about your skin, and only the last one can tell you what is about to happen rather than what already did.
Does Apple Watch track sun exposure?: Partly. Apple Watch Series 6 and later record Time in Daylight — the number of minutes you spent in daylight, measured with the ambient light sensor and stored in the Health app. It is a genuinely useful metric for circadian health, mood, and myopia risk in children, and it is the closest thing to a built-in sun exposure tracker on iOS. But it counts minutes, not intensity: twenty minutes at UV 2 on a January morning and twenty minutes at UV 10 at the equator both log as twenty minutes. Time in Daylight cannot tell you whether you are close to burning, because it has no notion of UV strength or your skin type.
How do you measure sun exposure?: The scientific unit is the standard erythemal dose, or SED, where 1 SED equals 100 joules per square metre of erythemally-weighted UV. It is a dose, so it accumulates: intensity multiplied by time. A convenient rule of thumb is that one hour of full exposure at UV index 1 delivers about 0.9 SED, so an hour at UV 6 is around 5.4 SED. Sunburn starts at your minimal erythemal dose (MED), which is roughly 2 SED for very fair Type I skin and around 10 SED for Type VI. This is exactly the arithmetic behind a personal burn time.
What is the difference between tracking daylight and tracking UV?: Daylight tracking counts time outdoors. UV tracking counts dose. They diverge sharply because UV intensity varies by a factor of ten or more across a day, a season, and a latitude — the same hour outside can be harmless or a burn. For circadian and sleep benefits, daylight minutes are the right metric and more is generally better. For skin safety, UV dose is the right metric and there is a hard ceiling. Most people want both, which is why Apple's Time in Daylight and a UV forecast app are complements rather than substitutes.
Can an app track sun exposure automatically in the background?: Not reliably, and it is worth understanding why before trusting an app that claims to. A phone in your pocket or a bag cannot see the sky, so any app inferring exposure from phone sensors is guessing. iOS also rate-limits background location and refresh aggressively to protect battery, so continuous logging is not something a third-party app can do accurately. The approaches that genuinely measure dose are hardware — a UV wearable or a single-use sticker worn on exposed skin. The approach that genuinely helps you plan is a forecast: the UV index for your location combined with your skin type, telling you how long you have before you burn rather than reporting afterwards that you did.
Are UV stickers and UV wearables accurate?: They measure real UV rather than a modelled forecast, which is their genuine advantage, and for people who need hard evidence of dose — photosensitive patients, outdoor workers — they are worth considering. The limitations are practical: a sticker or wearable reports the UV that landed on the device, not on the rest of you, so a sensor on your wrist under a sleeve reads near zero while your face burns. Stickers are consumables and wearables are another thing to remember and charge. For most people the forecast approach costs nothing and answers the same question a few minutes earlier, which is when the answer is still actionable.
How much sun exposure per day is safe?: There is no single number, because the ceiling scales with your skin type. Sunburn begins at roughly 2 SED for Fitzpatrick Type I, 2.5 for Type II, 3 for Type III, 4.5 for Type IV, 6 for Type V, and around 10 for Type VI. In practice, that means a Type II person has about 33 minutes of unprotected midday exposure at UV 5 and a Type V person has around 80 minutes at the same UV. Below the burn threshold, UV still accumulates as long-term photoaging and skin cancer risk, so the goal is not to spend your full allowance every day — it is to know where the ceiling is and stay comfortably under it.
What is the best sun tracker app?: It depends which of the four jobs you mean, which is why roundups of 'best sun tracker apps' tend to compare tools that aren't substitutes for each other. For sun position and shade planning, SunCalc and ShadeMap are the strongest and are free on the web. For logged minutes outdoors, Apple Watch's built-in Time in Daylight is already on your wrist and nothing third-party beats it. For a measured dose, a wearable like sun-a-wear or a single-use UV sticker is the only option that reads real UV rather than a forecast. And for knowing how long you can stay out before you burn, you want a UV forecast app that applies your Fitzpatrick skin type — Sunwise on iPhone, iPad, and Apple Watch. If the goal is the opposite — a timed tanning session or enough sun for vitamin D — SunDose and Vitamin D: Sun & UV Tracker are built around those jobs. Pick by the question you're actually asking, not by the star rating.
Is there a sun exposure tracker that works without a wearable?: Yes, with one honest caveat about what 'tracking' can mean without hardware. Your phone can't measure UV — there is no UV sensor in an iPhone, and a phone in a pocket can't see the sky anyway — so any app claiming to passively measure your dose from phone sensors is estimating. What a phone can do well is forecast: pull the UV index for your GPS location, apply your skin type, and tell you the minutes of safe exposure remaining. That covers the decision you can still act on. For the historical half, Apple Watch's Time in Daylight logs your minutes outdoors into the Health app with no extra app at all. Between them you get a ceiling and a log without buying a sensor.
Does Sunwise track my sun exposure?: Sunwise is a UV forecast app rather than a passive exposure logger — it does not run in the background recording where you have been, and it does not write to Apple Health. What it does is the forward-looking half of the problem: it takes the UV index for your GPS location from Apple WeatherKit, applies your Fitzpatrick skin type, and shows how many minutes of safe exposure remain at the current UV, updating as the UV changes through the day. For logged daylight minutes, pair it with Apple Watch's built-in Time in Daylight in the Health app. The two answer different questions and neither replaces the other.

Know the ceiling before you cross it

Sunwise is a personalized UV index and sunburn forecast app for iPhone, iPad, and Apple Watch. Set your Fitzpatrick skin type once and every UV reading turns into the minutes of safe exposure you have left — the forward-looking half of sun exposure tracking, alongside the daylight minutes your Apple Watch already logs. Hourly and 7-day forecasts, Apple Watch complications, and Lock Screen widgets keep it one glance away.