Couldn't you use the bleaching effect of UV to estimate exposure? It doesn't have to be an electronic UV sensor, just a spot of calibrated UV-sensitive dye.

That's similar in concept to the old style film badge dosimeters used to measure radiation exposure.

Unlike a film badge, a calibrated dye could be visually interpreted against a colour scale by the user. Neat idea if it works!

You want to avoid sunburn, while getting enough sun every day, so this wouldn't work if I understand your suggestion correctly.

There have been several wearable sensors that measure UV exposure:

https://www.wearshade.com/articles/comparison-of-wearable-uv... https://www.amazon.com/SunSprite-Wearable-Light-Tracker/dp/B...

I have the SunSprite and the June. The June is unreliable, I believe they stopped selling them years ago. The SunSprite worked well and once I'd worn it for a full year I had a good idea of my exposure at various times of year and stopped wearing it. The magnetic clasp on it sucked though, I would often find the sensor had slipped off and stuck to my car door (or anything else made of steel). Not sure if any of the sensors listed in the article are still for sale, but you can probably still find used ones on eBay.

You can also get simple wearable wristbands or tokens or cards that change color under UV exposure:

https://smile.amazon.com/gp/product/B004XMH95K https://smile.amazon.com/gp/product/B08HV91P77 https://smile.amazon.com/Fischuel-Photochromic-Indicator%EF%...

The cards are somewhat calibrated, but any of these technologies require taking into account your personal skin sensitivity.

The technology is out there, you could probably build your own sensor using an Arduino and UVA and UVB sensors. The SunSprite is cool in that it never needs charging since it charges from the Sun.

Cool, I didn't realize anyone else had productized UV sensors. I wish the tech would hit mass market devices.

> The technology is out there, you could probably build your own sensor using an Arduino and UVA and UVB sensors.

Back in 2016 or so, we were able to order UV sensors, but since there was so little knowledge about how to use them on wearable, getting them to work was a challenge.

It was months just to find a lens material that didn't block UV at all, but was also affordable, could be put on a production line, and fit all our consumer use cases (durable, chemical resistant, etc).

The cards are cool, I forgot about them.

It is unfortunate none of the main wearable players, by which I really just mean Apple, have bothered, but the UV sensor on Microsoft Band 2 was responsible for Band 2's not so friendly looking clasp, so I can't say I blame anyone for not wanting to go down that route again.

Edit: FWIW our sensor gave us something, I forget what, but I remember it wasn't what we wanted, and we had to map it to UVI. From what I vaguely recall it was one of those things where we ordered a sensor, it says it did one thing, but the thing it actually did was related but not quite the same, so we had to create a mapping curve of some type.

I came up with the user story and user flow for what we shipped, sun exposure reminders. We were really smart about it, we had logic in there to tell when you briefly went out of the sun, such as going to the bathroom, vs when you spent extended time inside, and we also worked to separate out walks to and from your car VS actually spending time outside.

To take "breaks", I believe we had an accumulator and if you went out of the sun we started a timer and if the timer went off we reset the accumulator but if you went back into the sun the timer was cancelled.

Actually starting the accumulator worked the same way, get out of car, exposure starts, if you didn't have so many minutes of continuous exposure, we never started the accumulator, an example is walking between buildings.

Lots of use case design around what ended up being a couple of dialog boxes for a reminder to put on sun screen!

Parents loved it though. :) Lots of positive feedback from parents who used it to track their family's sunscreen applications.

Edit: From shade

> 5 days of battery on a single charge

Pretty sure if we just ran the UV sensor on band our battery life would've been forever and ever. :-D

If that is a sales page, they need to list power draw of their sensor for various sampling rates, that is the only thing anyone cares about when it comes to integration.

> no current consumer devices exist on market that can track these two numbers

And if there were consumer devices, the next problem would be accuracy. Based on a bunch of reading I did several years ago (so maybe out of date), consumer excercise trackers were very innaccurate in many ways. Exercise misinformation devices.

> And if there were consumer devices, the next problem would be accuracy.

Having worked on Microsoft Band, I can tell you that accuracy is a problem with UV exposure for a number of reasons, none of which involve the sensor itself.

Mostly it is around how people wear it, and was the sensor always facing the sun, people going in and out of the shade, long sleeves, and so forth. We settled on # of minutes of high exposure, I forget what index we considered "high" but basically it if it was above a certain threshold we considered you "in the sun".

The goal was sunscreen application reminders, no way would we have trusted it to tell people they had "enough" sun!

Thanks; I am not surprised. It's hard to imagine how a sensor could be made to work cost-effectively - something that detects whatever ambient solar radiation slips through clothing? Whatever, consumers aren't going to pay for that.

But in fairness, the sensor doesn't work with how people use it. We could make a sensor that straps to user foreheads and requires them to always face the sun. When integration fails, we can point the finger either way, or just say it wasn't a good fit.