Thread

The UV index is not the warm sensation of sunlight on bare skin

99 points · 79 comments · evakhoury

Loading the complete thread in the background. This saved snapshot is available now. Refresh

xattt · 1790112634 · focus · HN ↗
I am curious if anyone else can tell whether it is a high UV day just by looking outside.
There is a certain look to the sky (slightly whiter-bluer) looking against the clouds, and I am not sure if it is because I am directly seeing UV, whether there is some fluorescence, or whether it’s placebo effect.
1. pazimzadeh · 1790113072 · focus · HN ↗
  UV index weighs UVB more heavily than UVA. UVB falls much faster than visible sunlight as the sun gets lower because photons travel through increasingly more ozone and atmosphere. So the higher in the sky the sun is, minus cloud clover, the higher the UV index is.
2. tomasphan · 1790114507 · focus · HN ↗
  I don't think so. If you controlled for temperature and season I bet you wouldn't be able to tell.
3. the__alchemist · 1790115951 · focus · HN ↗
  You can use simple heuristics to get a very good idea.
  1: How high in the sky is the sun? (Many other factors like time of year, time of day, and latitude feed into this) 2: What is the chance for you at a given time of the sun being blocked by clouds, buildings, etc?
4. magarnicle · 1790118263 · focus · HN ↗
  Maybe how different things look with sunglasses on vs off?
5. dlcarrier · 1790143859 · focus · HN ↗
  What your describing sounds a lot like the effect of humidity in the atmosphere. You can't see the humidity itself, but it affects how a smaller percentage of light is scattered, and that you can see, to the point that, when looking out from a high vantage point like a mountain or airplane, on clear dry days you can see further than on clear humid days.
pazimzadeh · 1790112939 · focus · HN ↗
> the sun may still feel pretty intense in the morning or late afternoon, but the risk of sunburn is considerably lower
This is very misleading. By some coincidence I was just looking into this earlier today.
The lower the UV index, the smaller the window is between the amount of time needed to get enough Vitamin D and the time to get burnt (erythema). So the best thing to do is get sunlight mid-day for a shorter amount of time.
UV Radiation: Balancing Risks and Benefits <a href="https://onlinelibrary.wiley.com/doi/10.1111/j.1751-1097.2008.00400.x" rel="nofollow">https://onlinelibrary.wiley.com/doi/10.1111/j.1751-1097.2008...
```
  As the UVI becomes smaller, it becomes more difficult to produce sufficient vitamin D without inducing erythema. For low sun conditions typical of midday in the mid-latitude winter (SZA ∼65°), where R∼1, the skin area exposed must be more than 12% (see Eq. 5) This means that for these low sun conditions it is improbable that sufficient vitamin D can be produced from exposing the hands and face alone, since that area is less than 12% of the full body.

  Figure 6 shows that for full body exposures, there is a wide window between the time for sufficient UV and the time for too much UV. As the fraction of body that is exposed decreases, the window of optimum UV exposure times also decreases. If only hands and face are exposed, there is generally only a small window between receiving insufficient UV for vitamin D production, and too much UV for skin damage (erythema).
```
You would do well to calculate the numbers for your own city, as I did earlier today for mine:
<a href="https://chatgpt.com/share/6ab2f272-a32c-83ea-9fec-49031e4da362" rel="nofollow">https://chatgpt.com/share/6ab2f272-a32c-83ea-9fec-49031e4da3...
1. foota · 1790113245 · focus · HN ↗
  Isn't think only true if getting enough vitamin D is as important to you as cancer?
  1. pazimzadeh · 1790115315 · focus · HN ↗
    Sunlight is associated with lower risk of almost every cancer except skin cancer, and skin cancer is the easiest to detect early.
2. happytoexplain · 1790113256 · focus · HN ↗
  I really appreciate learning this fact, but I can't tell how it makes the quoted sentence misleading. The author is just talking about the disparity between how warm it feels and how fast you will burn. They don't mention vitamin D.
  1. pazimzadeh · 1790113795 · focus · HN ↗
    I know they don’t mention vitamin D, but I think it’s important for people to know the context and not think that late day sunlight automatically = better
    andrewflnr · 1790115316 · focus · HN ↗
    That's good to know as an additional factor to consider, but it's not enough to justify your accusation that the original statement is "misleading".
    You're allowed to just say "cool, here's another important thing to think about it". You don't have to pick a fight.
    pazimzadeh · 1790115467 · focus · HN ↗
    I think the original statement was misleading wrt sunburn for the reason I stated. I think we have different definitions of fight.
    happytoexplain · 1790116724 · focus · HN ↗
    Ohh, I see. I'm not sure it was "very misleading", but I agree somebody trying to decide when to get sunlight for the purposes of vitamin D could easily misapply the lesson from this article.
3. prometheus1992 · 1790114295 · focus · HN ↗
  it really only takes about 5 minutes of exposure to get the vitamin D your body needs. i would happily do it between 7-9AM when the UV is low than doing it at mid day.
  1. an_account · 1790116044 · focus · HN ↗
    You only need 5 minutes at midday in the summer. At 7am, you get essentially no vitamin D.
  2. pazimzadeh · 1790117822 · focus · HN ↗
    What you are saying is exactly the wrong takeaway. Please read the article:
    <a href="https://onlinelibrary.wiley.com/doi/10.1111/j.1751-1097.2008.00400.x" rel="nofollow">https://onlinelibrary.wiley.com/doi/10.1111/j.1751-1097.2008...
    Beneficial UV is UVB, which is low when the sun is low because it can’t get through the ozone and atmosphere as well when the sun is at an angle. Instead, you are getting mostly UVA, which has an easier time passing through the skin and doesn’t stimulate vitamin D production.
4. the__alchemist · 1790115761 · focus · HN ↗
  The statement you quoted is very useful [One of the most useful heuristics], and your statement is misleading. You accumulate damage (Photoaging, cancer risk) dramatically faster at high sun angles (i.e. mid day, close to the summer solstice, closer-to-equatorial latitudes) etc than low ones.
  I am not trying to be negative, but this is very important if you have pale skin. Being outdoors in morning and late afternoon is dramatically less damaging than mid day.
  1. happytoexplain · 1790117021 · focus · HN ↗
    It kind of depends on context.
    If your goal is "hang out in the sun but don't get burned", then morning/evening is better. If your goal is "get exactly as much vitamin D as I need while minimizing UV damage, perhaps using a timer", then it sounds like technically mid-day is better.
    the__alchemist · 1790117410 · focus · HN ↗
    After reading your reply here and the one I was responding to, I think I understand (You spelled out) the disconnect; the post I replied to was about Vitamin-D-Maxxing, which isn't something I had in my cross check. My primary concern is "Which times should we do outdoors things to prevent sun damage [photoaging + caner]" (And/or "Do I need to apply sunscreen before going out now / how long can I stay out)
    pazimzadeh · 1790117529 · focus · HN ↗
    Yes, mid-day for a shorter amount of time is better for optimal Vitamin D. The article I linked above goes into great detail about it, more than the two quotes I pulled out
GuB-42 · 1790113215 · focus · HN ↗
I think I got the worst sunburns when I didn't feel hot at all.
Usually, it involves water, water cools you down, so you don't feel the heat, but it doesn't block UV, so you don't get the warning.
1. koolba · 1790116675 · focus · HN ↗
  Overcast days are the worst offenders for sunburn because the melanin impaired don’t feel the heat of the sun to remind them they are going to roast.
  1. cortesoft · 1790116816 · focus · HN ↗
    I have always heard sunny snow days are the worst, because you feel cold, but the sun is still hitting you, plus reflecting off the snow to hit you twice.
    nephihaha · 1790116968 · focus · HN ↗
    You can get sunburn from light reflecting off water as well, in hot places. Maybe not on its own, but certainly in conjunction with direct sunlight.
  2. nephihaha · 1790116855 · focus · HN ↗
    Depends which part of the world you are in. I've never been sunburnt on an overcast day where I live.
    saltcured · 1790117966 · focus · HN ↗
    One of my worst sunburns was in San Diego on an extremely gray day. I should have known better.
    The right thickness marine layer can make the sky seem dim but it's like one massive UV diffuser from horizon to horizon.
  3. pazimzadeh · 1790119709 · focus · HN ↗
    They are also the worst because you get mostly UVA since UVB has a harder time penetrating through cloud cover
  4. bwnkl · 1790138233 · focus · HN ↗
    I agree that it very much depends on latitude and time of year. In most of Europe, overcast days usually don't present much of a problem for me, but I remember spending a day at the beach in Ecuador under very dense cloud cover and getting one of the worst burns I've ever had
2. nephihaha · 1790116789 · focus · HN ↗
  It depends a lot on the position of the sun in the sky too. It can be warm around sunset and sunrise, but because the sun is so low to the horizon, it is passing through more atmosphere.
  I spent a lot of time out in the sun by the Dead Sea and did not burn at all, since the very low altitude seems to have provided me with extra protection, whereas nearby on the shores of the Red Sea, at sea level, I did burn with similar levels of exposure.
  1. cindyllm · 1790122239 · focus · HN ↗
    [dead]
3. piltdownman · 1790168065 · focus · HN ↗
  Anecdotally from an Irish dermatologist - the majority of her clients under 30 are holiday sunburn casualties from either Iberian waterparks or activities like snorkeling/skin-diving in SEA. The ones over 30 are basically all farmers.
kens · 1790113398 · focus · HN ↗
The details of UV damage are interesting. You can think of DNA as a sequence of four letters: C, G, A, and T. If there are two neighboring T's, UV can move a bond, linking the two T's together (i.e. thymine dimerization). If you're in the sun, each skin cell gets 50-100 of these pairs created per second (which is much higher than I expected). Enzymes fix most of these errors, but sometimes the errors will cause problems during DNA replication and you can end up with mutations.
Details: <a href="https://pdb101.rcsb.org/motm/91" rel="nofollow">https://pdb101.rcsb.org/motm/91
1. pazimzadeh · 1790119654 · focus · HN ↗
  And UVB light can actually promote DNA repair pathways
  Enhancement of UVB-induced DNA damage repair after a chronic low-dose UVB pre-stimulation
  <a href="https://www.sciencedirect.com/science/article/abs/pii/S1568786417301635" rel="nofollow">https://www.sciencedirect.com/science/article/abs/pii/S15687...
Terr_ · 1790113424 · focus · HN ↗
> Sunburn is triggered when your DNA is damaged from light absorption [...] This interferes with protein synthesis and wreaks havoc in your body over time
Not a skin-scientist, but this seems misleading: Sunburn is not caused by some bad DNA floating around, nor damaged cells making making mistakes or pumping out wrong proteins to inflame their neighbors.
Instead, your cells have techniques to measure a variety of risk factors and signals (which does include DNA-molecule weirdness [0]) and when things get too risky the well-behaved ones will self-destruct, to avoid the chance of turning into a cancer.
So the sunburn you see and feel is instead due to cells signalling "something damaged me and I can't be trusted, I'm shutting down, recycle me" to your immune-system, plus the attendant bustle of hazmat-cleanup and increased security-sweeps for cancer-leftovers and other potential causes of the damage.
[0] <a href="https://www.nature.com/articles/newbio241074a0" rel="nofollow">https://www.nature.com/articles/newbio241074a0
1. skullone · 1790114459 · focus · HN ↗
  This whole article shouldn't even exist, and should just point to wikipedia or mayo clinic.
2. EA-3167 · 1790120029 · focus · HN ↗
  DNA is the instruction set for protein synthesis. If your DNA is damaged beyond repair that's an issue, and sure apoptosis is the usual result and not cancer. At the same time however when cells die either from the direct impact of DNA damage or apoptosis they both stop working and spill their contents into the area... including signalling molecules that promote inflammation.
  The sunburn you feel isn't a distress signal from cells warning that they can't be trusted, it's tissue death and an inflammatory reaction triggered by a cytokine response.
  1. Terr_ · 1790214665 · focus · HN ↗
    [delayed]
3. somat · 1790133922 · focus · HN ↗
  Another interesting way to consider it is that a sunburn is a really mild case of radiation sickness.
  Or the other way radiation sickness is the deepest worst sunburn you have ever had.
4. rogerrogerr · 1790134235 · focus · HN ↗
  Our immune system is _so cool_. Seems like every week I learn something new about it.
  1. Terr_ · 1790148268 · focus · HN ↗
    [delayed]
  2. Terr_ · 1790148387 · focus · HN ↗
    [delayed]
skyberrys · 1790113894 · focus · HN ↗
Toasting my DNA is quite a way to put it. It's an informative read, it helps me understand why the noonday sun does feel so intense. Even if it's not hot, the ability to find shade at noon is so poor, it feels inescapable.
avidiax · 1790114317 · focus · HN ↗
Does anyone know how UV indexes reported by weather apps (including forecasts) work?
I've found that some sources report lower UV index on cloudy days, whereas some seem to indicate the same index as a sunny day.
It's not clear if these sources all have a different model for UV, some being more sophisticated or conservative, and whether any of them are backed up by a UV meter.
1. asdff · 1790114532 · focus · HN ↗
  It is a prediction of UV intensity based on specific forecast location, time of day, day of year, prevailing weather, and any anomalies affecting the ozone layer.
  1. ViscountPenguin · 1790116143 · focus · HN ↗
    This depends on the country and the source. Here in Australia BOM UV values are predicted, but cancer council are observed.
    magarnicle · 1790118112 · focus · HN ↗
    Here are the predictions and observations for Australia: <a href="https://www.arpansa.gov.au/our-services/monitoring/ultraviolet-radiation-monitoring/ultraviolet-radiation-index" rel="nofollow">https://www.arpansa.gov.au/our-services/monitoring/ultraviol...
    Gigachad · 1790126169 · focus · HN ↗
    From this it seems like the predictions are actually really accurate.
    asdff · 1790127953 · focus · HN ↗
    What is cancer council?
2. dlcarrier · 1790144142 · focus · HN ↗
  Some phones and watches have UV sensors in them, and you'll usually see a 20%+ drop in live readings when under an overcast layer, compared to direct sunlight, but prediction models can't easily model when clouds will be where, so they either ignore them or use an average affect.
Avicebron · 1790115923 · focus · HN ↗
My mind is so brainrotted I clicked on to this thinking "that's a weird complaint about a package manager"
cryptolobster · 1790115959 · focus · HN ↗
[dead]
nomel · 1790116546 · focus · HN ↗
I don't know about this. I can feel where there are holes in my sunblock (which only block UV) which lets me know where to apply it, and the sensation is not one of heat of the sun, it's different. I'm not sure about the mechanism, but the presence of the sunblock stops the "UV" type sensation. This from the moment I put it on to long after the water component of the sunblock has evaporated. And, the type of sunblock doesn't matter (the drier waterproof kind or various lotion varieties). And, I do notice a difference between the different SPF, along with some "bad" sunblock that I just kept applying but couldn't make the feeling go away (it had apparently separated, everyone was burned).
1. crazygringo · 1790123344 · focus · HN ↗
  Thank you -- I'm exactly the same. You're right, it doesn't feel like heat, it feels like... something else, I have no words for it.
  It usually goes together with bright direct sunlight in the summer, so I think most people don't learn to notice or distinguish it.
  But I find that it's on particular overcast days in the summer, when there is no direct sunlight, that you can feel it intensely without the accompanying sunlight/heat. It reminds me to put on sunblock. But it's not all overcast days -- it's strongest when there's a light cloudy "haze". In contrast, when it's thick clouds approaching thunderstorm, you obviously don't feel it at all.
  So it's that kind of thing that's hard to judge before you go outside, but as soon as you do, you get a clear "oh, I definitely need to go back in and put in sunblock" or "oh, this is fine, no sunblock needed today".
  The best way I can explain it is as kind of an "oppressive" feeling, almost like a kind of pressure on your skin. Like, you can describe heat that way too -- oppressive or like a kind of pressure -- but in this case, you're feeling those things when there is no heat.
  1. phonon · 1790125237 · focus · HN ↗
    "no words for it"
    Actinic?
    <a href="https://www.merriam-webster.com/dictionary/actinic" rel="nofollow">https://www.merriam-webster.com/dictionary/actinic
  2. kgc · 1790133098 · focus · HN ↗
    Also get the pressure feeling, but via eyes.
  3. stogot · 1790136557 · focus · HN ↗
    It is a numb pressure for me
2. taneq · 1790124432 · focus · HN ↗
  I’ve always thought of sunblock as taking the ‘sting’ out of the sunlight. It’s a separate sensation that I can feel even on a cold day.
  This is in Australia where the hole in the ozone layer often results in 10x ‘normal’ UV levels, you can get noticeably burned in a few minutes.
  1. meatmanek · 1790125767 · focus · HN ↗
    > This is in Australia where the hole in the ozone layer often results in 10x ‘normal’ UV levels, you can get noticeably burned in a few minutes.
    By 10x you mean 10% more, and by ozone layer you mean the fact that the southern hemisphere's summer coincides with Earth's perihelion while the northern hemisphere's summer coincides with aphelion.
    <a href="https://www.abc.net.au/news/science/2025-02-04/sun-summer-uv-sunburn-skin-cancer-australia-ozone-layer/104870806" rel="nofollow">https://www.abc.net.au/news/science/2025-02-04/sun-summer-uv...
    esrauch · 1790128267 · focus · HN ↗
    I expect they just meant UV 10, which is 10x the energy of UV 1.
  2. jandrewrogers · 1790128796 · focus · HN ↗
    Australia’s UV is only modestly higher than other places at similar latitude. It is similar to equatorial regions and isn’t remotely close to 10x anywhere. You can experience the same UV index in the tropics.
    Some parts of South America have a UV index twice that of Sydney’s maximum. All of the actually extreme UV index locales are extreme altitude and near equatorial.
    piltdownman · 1790167857 · focus · HN ↗
    The Peruvian Andes has the most extreme UV index in the world due to being 10,000ft+ above sea level and on the most susceptible line of latitude. That being said, even with the atmospheric deficit, the max peak recorded by ground and local meteorological observations was 18. Can't seem to find a citation for 2x Sydneys max (14/15).
    Indeed looking at Oceania; Sydney, Perth, and Auckland all hit 14/15 regularly in the Summer months. Auckland in particular has ~40% more UV than comparable northern latitudes.
    Given the genetics and immigration is heavily skewed in favour of the British and Irish diaspora, it's about 3x the UV Index of what the UK and Ireland see. Dunno where 10x came from.
    jandrewrogers · 1790179744 · focus · HN ↗
    The UV index is >20 in the Andes of the northern Atacama. It is considerably stronger than the tropics thanks to the extreme elevation and ~0% humidity. The global record for UV is at Licancabur on the Chile/Bolivia border with an index of 26-43 (the exact numbers are apparently contested). We only know this because scientists study the unusual lake there. Some other places in the region that few people visit are almost certainly higher based on their geography.
    The highest UV index I can find for Sydney is 14, which is typical of many places in the tropics.
    I've spent time in the 20+ UV of the northern Atacama and it is a different beast. The indirect UV reflected by the soil is strong enough to burn you even if you are not exposed to direct sun. It requires precautions that I never needed in Australia or elsewhere in the tropics.
3. samusiam · 1790127275 · focus · HN ↗
  After you sure that isn't because your skin is moist where sunblock was recently applied, and therefore cooler?
  1. esseph · 1790131452 · focus · HN ↗
    [delayed]
    jrochkind1 · 1790132295 · focus · HN ↗
    Sunblock is not supposed to reflect heat (infrared). It's supposed to reflect UV. Different spectrum. Kind of the whole thing the OP was about. I have no idea if sunblock also reflects infrared though, incidentally.
    <a href="https://care360.basf.com/emea/en/industries/personal-care/core-competencies/all-about-sun/sun-protection/how-do-they-test-a-sunscreen-s-protection-factor" rel="nofollow">https://care360.basf.com/emea/en/industries/personal-care/co...
    dreamcompiler · 1790175198 · focus · HN ↗
    Sunblock mostly absorbs UV (and turns it into heat). Some reflection occurs but it's mostly absorption.
    esseph · 1790181435 · focus · HN ↗
    [delayed]
    dreamcompiler · 1790185349 · focus · HN ↗
    I thought so too but it's not the case. Even the mineral sunscreens mostly absorb.
    <a href="https://cen.acs.org/business/consumer-products/What-in-sunscreen-and-how-does-it-protect-your-skin-from-the-sun-rays/99/i27" rel="nofollow">https://cen.acs.org/business/consumer-products/What-in-sunsc...
    nomel · 1790194493 · focus · HN ↗
    Video with a UV camera is interesting: <a href="https://www.youtube.com/watch?v=E9tEEDpeJoo" rel="nofollow">https://www.youtube.com/watch?v=E9tEEDpeJoo
    Black means absorbed, of course.
    nomel · 1790276573 · focus · HN ↗
    And, omg, you can buy an active version on amazon, for this exact purpose: sunblock coverage check!
    <a href="https://www.amazon.com/s?k=uv+mirror+for+sunscreen+test" rel="nofollow">https://www.amazon.com/s?k=uv+mirror+for+sunscreen+test
herf · 1790117121 · focus · HN ↗
Good post - the UV index is related to how short the "column of air" that the sun traverses to get to your skin - noon is the shortest distance. Scattering is a density function (more air, more scattering), so this is why it looks like cos^p when compared to normal irradiance (cos). It also explains why it is hard to get a sunburn in the temperate winter, since the sun always appears at an angle, it doesn't go directly overhead.
1. saltcured · 1790117864 · focus · HN ↗
  As someone who has gotten sunburned in California winters and even around 7-9 PM in Alaska, I can't relate to your closing idea at all!
2. xdavidliu · 1790159195 · focus · HN ↗
  i'm not an expert but i think you might be conflating uva and uvb. uvb is the one that goes to zero in winter and near sunrise and sunset, is completely blocked by glass, and requires being near solar noon to have maximum effect (i.e. highest when your shadow is shorter than you). It is also the one that is responsible for vitamin D synthesis.
  on the other hand, uva is the one that is still substantial in winter and away from solar noon, goes through glass easily, and can cause sunburns and skin cancer.
YesBox · 1790117164 · focus · HN ↗
I've heard a quick way to determine if the UV index is dangerous is if your shadow is shorter than you. Though location matters too.
I moved from Vermont to Texas and had to purchase an umbrella with UV protection to walk around during the day. The highest the UV index hits in the Vermont's summer is 6. In Texas, it's 11+ !!! 15 minutes and you're toast
1. jandrewrogers · 1790118697 · focus · HN ↗
  In some parts of South America the UV index reaches 15-20 due to near-equatorial latitude and extremely high elevation. It is strong enough that you need protection from indirect UV radiation.
2. pazimzadeh · 1790119810 · focus · HN ↗
  Not quite. Shorter exposure when your shadow is short is better than longer exposure when your shadow is long, in terms of sunburn/vitamin D tradeoff
  <a href="https://onlinelibrary.wiley.com/doi/10.1111/j.1751-1097.2008.00400.x" rel="nofollow">https://onlinelibrary.wiley.com/doi/10.1111/j.1751-1097.2008...
  1. AmazingEveryDay · 1790120946 · focus · HN ↗
    From conclusion of paper, I read the opposite of what you state. "A better strategy would be to expose a larger fraction of the body for a shorter time period, preferably when the sun is lower in the sky to allow a greater margin of error."
    A sun lower in the sky means your shadow is longer. Maybe I'm confused?
    pazimzadeh · 1790121878 · focus · HN ↗
    Good catch, it is kind of confusing as they seem to contradict themselves, and also depends on the season.
    Figure 6 shows that for full body exposures, there is a wide window between the time for sufficient UV and the time for too much UV. As the fraction of body that is exposed decreases, the window of optimum UV exposure times also decreases. If only hands and face are exposed, there is generally only a small window between receiving insufficient UV for vitamin D production, and too much UV for skin damage (erythema). As the UVI becomes smaller, it becomes more difficult to produce sufficient vitamin D without inducing erythema. For low sun conditions typical of midday in the mid-latitude winter (SZA ∼65°), where R∼1, the skin area exposed must be more than 12% (see Eq. 5) This means that for these low sun conditions it is improbable that sufficient vitamin D can be produced from exposing the hands and face alone, since that area is less than 12% of the full body.
    If you are able to expose a lot of your body at a time then yes later in the day is workable (in the summer). In the winter, (depending on your latitude) you still need mid day sun to make any meaningful Vitamin D.
lemming · 1790120455 · focus · HN ↗
I live in New Zealand, and my wife is Spanish so we’ve spent a bunch of time in Spain too. NZ for a combination of reasons has much higher UV than Europe, with the corresponding skin cancer rates. In midsummer the UV is around 150% of what it would be in Europe at the equivalent time of year, but here, especially if it’s windy, it might feel like 20 degrees and you’d quite like to be in the sun, whereas in Spain you’d probably be at 40 degrees and there’s no way you’d want to be out of the shade. The difference is really stark, in general there I can regulate my sun exposure by feel much more than I can here.
DStiego · 1790124906 · focus · HN ↗
For this very reason, I’ve set the watch face on my Apple Watch to always show UV index.
It allows you to gauge whether you should maybe wait under that tree over there while waiting for a friend.
In Australia for example, this is a matter of life and death! There are skin cancel clinics around every corner (no exaggeration).
efavdb · 1790129323 · focus · HN ↗
Strange. I thought a pale person would reflect more light so they’d burn less (obviously contrary to what we see). But apparently the resolution is that the uv is absorbed safely not reflected
Oscalemor · 1790194914 · focus · HN ↗
Makes me think of the nice shade of pink I get from hitting the ski-slopes. Cold, but daunting.

Open on Hacker News to reply ↗

Unofficial Hacker News client; not affiliated with Y Combinator.