Tips on how to quantify time spent outdoors and/or sunlight?

I have a skin condition (psoriasis) and am considering starting to quantify the number and total surface of the spots on my skin in order to relate these to several factors of my life (stress, weight, activity, sleep, etc). Another factor that is suggested to influence this condition is sunlight, and I do have the idea it might be an important factor.

I am therefore considering quantifying how much time I spend outdoors and/or how much sunlight I caught each day. The first thing that came to mind was to use a self-questionnaire, but I’m not sure how valid this measurement would be. Estimating the time spent outside could introduce bias, but also how I was dressed during my time spent outside and therefore how much skin was exposed to sunlight.

Another option I am considering is using the Life Cycle app that tracks your position using GPS and quantifies how much time you spend on the road, at home, at work etc. However, for some reason it doesn’t register my runs (ca 5 km) and just says I were at home, so I can’t fully rely on it.

Does anyone have any suggestions on how to quantify these aspects? Thanks for your thoughts!


One post-factum way to calculate this exposure could be the following:

  1. Get access to a dataset containing hourly entries for the weather, starting with sunrise and ending at sunset - for each day of the year and for your specific location on earth during that hour
  2. From datatset in #1, remove entries when sun where sun wasn’t shining
  3. From dataset in #1, remove the hourly entries for those hours of the day when you are certain to be indoors (e.g. in the office, at the gym etc, commuting, eating) over the course of the year

What remains is a list of hourly entries when the sun was shining at your location, and when you were possibly exposed to the sun. From this, you can further remove / leave entries based on your knowledge of being indoors or not but this will vary much more day-to-day.

This is more a post-factum approach that could be done without the GPS tracking you mentioned (or the confidentiality issues!) If you are more interested in an up-to-date monitoring approach, you could combine the dataset above with GPS tracking and calculate it that way.

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Have you considered this?


That’s quite interesting Gary, I haven’t seen that one before but it looks like it could be really useful for my plan. Unfortunately it doesn’t ship outside of the United States according to the website (I live in the Netherlands), but I contacted the company just in case. Thanks for the tip!

Update: Actually, the company itself doesn’t ship outside the US but through I just ordered it. I think I’ll combine a self-questionnaire and this tracker for now but if the tracker works adequately it should do the job.

Thanks Sergio, that actually might work. I haven’t found a weather site that shares the type of needed weather data, but maybe I’ll run across one later, I’ll give it another thorough look.

BTW, I found that using questionnaires for recalling time spent outdoors is actually quite common (link with example), although most questionnaires ask for a recall over a much longer time period than one day. I’ll give both another look and will see what appears to be both reliable and feasible. Thanks again!

You might want to check out dMinder. I use it to track my sun exposure and estimate vitamin D levels:


Herman - are you going to be at QS17 - if so let’s consider a how-to session on sun exposure, vitamin D, and related topics…

I’ve used the Sunsprite and rather liked it for helping me with seasonal depression. I’ve had my eye on this cheap bracelet that tracks UV exposure during the day. There is no way to get data out, though and I don’t know how reliable the sensor is.

There’s a company called LYS that says they’ll have a tracker out this fall with a feature set pretty similar to Sunsprite, but with the added ability to track color temperature. They are more concerned with circadian rhythms, than limiting exposure, though.

Definitely let us know what you think about the Sunsprite!


I’ve considered going to QS17 Gary, but have social obligations elsewhere that weekend. A session on sun exposure and vitamin D would be very interesting though!

The Sunsprite tracker I ordered will arrive around march 7th, since overseas shipping will take a while. I’m very interested to see how it works and what data comes out. I’ve pretty much planned how to track my other variables (just considering some questionnaires for subjective measures like stress and fatigue) and am planning to measure data for at least a year. I found out there’s actually a medical tool to calculate the severeness of my skin disorder (the PASI) and will measure it once per week, so in one year I should have 52 data-points to calculate a prediction model on, if that’s sufficient. I’ll make sure to share my findings around here by then, I’ll probably write a blog or an article on it.

Thanks again for sharing your ideas, also for Sergio, Bob and Steven (that LYS sounds nice also btw)!

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Weather Underground is a pretty good source for reliable archived weather data including the hourlies. Otherwise, try your national weather service. They usually publlish weather data going back several years as well.

I have a daily question to estimate my sun yesterday. You probably want more specific than that. And you probably want to track allergens too including foods, plants, chemical exposure including washing powders, cleaning products…