Thread

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

99 points · 79 comments · evakhoury

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...
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  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).
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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. 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 surprising 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.

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