Show HN: I built a daily sunlight tracker
lumehealth.ioI kept trying to explain how important outdoor light is and how most people aren’t getting enough. Eventually I figured that showing is more effective than telling.
So we built a free app that uses your Apple Watch or iPhone to automatically track your light exposure throughout the day.
It tells you if you’re getting enough, shows you how consistent you are, and rewards habits that support hormone balance.
It's in beta on TestFlight, let me know what you think!
>how most people aren’t getting enough
What are you basing this on? What counts as 'enough'? And how are you tracking light exposure?
"In the Fall of 2023, Apple introduced a new metric called “Time in Daylight” as part of watchOS 10 with Apple Watch Series SE (second generation) and Apple Watch Series 6 or later. This metric uses the ambient light sensor in Apple Watch and an associated algorithm to estimate how much time is spent in daylight and maximum intensity (lux) in 5-minute increments."
https://appleheartandmovementstudy.bwh.harvard.edu/summer-da...
Couldn't find any direct source from Apple tho
There are countless studies that billions of people are Vitamin D deficient. Our bodies are designed to get most of that from the sun. Lots of people never even leave their house on a given day.
https://pmc.ncbi.nlm.nih.gov/articles/PMC3068797/
I should've been more specific. The study you link states that 'To prevent vitamin D deficiency, one should spend 15 to 20 minutes daily in the sunshine with 40% of the skin surface exposed.'. The screenshot on lume health shows a goal of 120 minutes.
Moreover, sun exposure is not by definition 'healthy'. Spending two hours in the sun at noon in the middle of summer does more harm than good.
> Nonsmokers who avoided sun exposure had a life expectancy similar to smokers in the highest sun exposure group, indicating that avoidance of sun exposure is a risk factor for death of a similar magnitude as smoking.
https://pubmed.ncbi.nlm.nih.gov/26992108/
The study seems to be incredibly flawed.
> Women with active sun exposure habits were mainly at a lower risk of cardiovascular disease (CVD) and noncancer/non-CVD death
Not surprised there because people who spend more time outdoors will typically be participating in physical activity at the same time, while people who avoid sun exposure will typically be seated while participating in sedentary activities.
If we want to see if sun exposure is the sole reason for longevity, we will have to force the subjects to sit on a couch outside.
Claiming that not getting sunlight is the same as smoking is pure garbage.
> Claiming that not getting sunlight is the same as smoking is pure garbage.
So you're throwing out a whole study because it didn't cover a specific confounding variable you thought of, than stating a claim with no evidence backing it up?
That's pure garbage.
They specifically call this out in the abstract.
> We obtained detailed information at baseline on their sun exposure habits and potential confounders.
https://pubmed.ncbi.nlm.nih.gov/24697969/
> The study you link states that 'To prevent vitamin D deficiency, one should spend 15 to 20 minutes daily in the sunshine with 40% of the skin surface exposed.'. The screenshot on lume health shows a goal of 120 minutes.
Linearly it follows that if one wears clothes that cover more than 40% of lit skin, then the duration would be adjusted to match the total skin-area/time.
If one start with 1.85 m^2 body surface area, 40% of that is .72 m^2. If clothing covers 50% of a human and the human's shape and hair occludes half of that remaining, you have .46 m^2 available for sunlight. .72 m^2 * 20 is 14.4 m^2/min. divided by .46 m^2 it seems that 31.3 min would be the daily amount.
This seems much less than lume health's goal of 120 min. Otoh, given there is less opportunity for get to 14.4 m^2/min daily (I'm looking outside at a nice rainstorm), maybe the 120 min has some catchup factor?
Yes, you get your sun in the morning and/or in the evening. This is standard.
Morning and evening sun are excellent due to the high levels of Near-IR and IR. However, it is devoid of UVB needed for vitamin D synthesis. You need morning, evening, and midday sun.
I think this mostly has been debunked in the last 15 years, except in the unscientific health influencer space
https://pubmed.ncbi.nlm.nih.gov/39017376/
Really the conclusion of that paper, that people are not vitamin D deficient, ought to be that people are sunlight deficient. This is why studies that involve supplementation of vitamin D frequently show no effect. Vitamin D is only one of many many ways in which light affects biology.
The paragraph near the end about babies needing fortified milk because breast milk is insufficient in vitamin D is laughable. It seems pretty obvious that babies are one of the most, if not the most, sunlight deficient demographics.
Where is the data here? That article simply declares that there is a global epidemic of vitamin D deficiency and I followed the citation it gives to back that up, which is this: https://www.sciencedirect.com/science/article/pii/S000291652.... Except this citation is also not a study. It's an opinion piece that just declares people are vitamin D deficient without doing any measurements of how much vitamin D anyway has circulating in their blood. It appears to be a narrative review, not a study.
I'm not saying the claim is for sure wrong, but at some point, to make this claim, someone has to have actually measured vitamin D levels in some broadly representative sample of humans and you could post that instead of whatever came up first in Google Scholar when search for "vitamin D deficiency."
This paper has a chart (figure 2) of the disease incidence prevention by serum vitamin D levels above the baseline of 25 ng/ml.
https://www.researchgate.net/publication/276034276_Vitamin_D...
Nice! An Android version would also be appreciated :)
Working on it! Thanks for the feedback.
Looks cool!
A couple questions:
(1) Are you supposed to join the waitlist to use this ("Get Early Access"), or can you just start using via TestFlight ("Download Today")? I see two different links on this page.
(2) How does this app measure the amount of light received by the Apple Watch? Does the Watch have such sensors and expose such APIs?
Thanks (1) You can join the waitlist for our hormone tracking device, the app is available for download today on TestFlight. Eventually the app will be used to show you the connection to your hormone balance (like cortisol etc.) and your light exposure. They are very tightly linked! (2) there is a light sensor in the display of the Apple Watch that automatically tracks it. It works ~80% of the time, but struggles if you have a big jacket
Most people have their phone in a pocket or purse or similar while outdoors. Wouldn't this require the phone to be out and exposed to light in order to work correctly? So not only are you trying to get people to change habits of getting outside, you're also requiring they change habits with the devices as well. Good luck with that, and I mean that with more sincerity than snark but not no snark.
The light sensor is in the Apple Watch display (behind the screen) it's what it uses to adjust the screen brightness. So if it's exposed to the sun it will count it automatically
Looks beautiful! Here are some thoughts:
- Having a dark theme seems logical for an app focused circadian rhythms, would be nice to have a dark appearance
- Not being able to switch between days by swiping felt quite annoying: the Home page requires two taps to change to another day, and the Progress page needs one — but it could’ve been a swipe. And the calendar on the Day page can’t be swiped down, only closed by tapping on the (x).
I hadn’t even realized that Apple had rolled out Time in Daylight — Apple Health hasn’t promoted or highlighted it like it does for other new Categories, and even then, the visualization still feels lacking.
I have been trying to get more consistent morning natural light exposure lately, so this is perfect timing!
Thanks so much!
Appreciate the feedback. Will add those updates to our list of things to change (lots of improvements to make).
Glad to hear you're getting more consistent morning light, it's imo one of the most powerful things you can do for your health.
> I hadn’t even realized that Apple had rolled out Time in Daylight
Unfortunately, it is not the most accurate. If you wear full sleeved clothing which cover your Apple Watch, it will report wrong numbers.
Yeah unfortunately you have to have the screen exposed for a few minutes each time you go outside.
I spoke to the team at Apple, they said as long as you have a couple of minutes in the sunlight while you're on a walk it will then use sensor fusion to count the rest of the time outside.
Why everything these days it's an app /rant
Pretty cool! I’m working in this space right now with architects and building owners. The science has advanced unto a certain knowing of melatonin secretion getting in the way of mental alertness under poor artificial illumination.
Hit me up if you’re interested in learning more or how I can move your office space towards a renovation on the build owners dime: joseph@ledcompliant.con
Thanks! Reaching out.
Hormone optimization is just the newest way of calling someone the f slur since it’s not cool anymore.. f slur, soy, cuck, incel, now I also have to worry about how much sun I get if I want to avoid bullying. Give me a break
ummmmmm, if you dont have some kind of tan lines, you are not getting enough sunlight the app is pre loaded at birth .......though,I get it, as there is a significant demographic who will only trust there (beloved) device, and will benifit from the prompt, perhaps, perhaps not, as there is no possible way to break out all of the inumerable ways that human phisiology has adapted to ambient conditions on our planet, into seperate apps, so.....
I get what you're saying.
The product we're working on in the background is a wearable hormone monitor that actually shows you at the molecular level how much sunlight impacts your hormones - we've found this to be the most powerful lever for behavior change. But in the meantime, we have been using the saying "you can't improve what you can't measure" to help people get more sunlight.
I'm with metalman on this.