Stephan: You don't need to worry too much about the UVA component from a skin damage perspective. Both UVA and UVB are attenuated by the atmosphere, just more so for UVB than UVA. Although there's a lot more UVA than UVB, it's the shorter wavelength higher-energy UVB photons that cause most damage. In fact, the 'action spectrum' for skin damage decreases so steeply with wavelength that for high sun elevations, the contribution towards skin damage from UVA wavelengths is only about 5% of that from UVB wavelengths (that fraction does increase at lower sun elevations, but by then the total is in any case much smaller). I might talk about it in a later post.
Thanks Richard. Your detailed explanation of the difference in atmospheric absorption of UVA versus UVB for different elevations of the sun makes sense. It helps me plan and control the right amount of sunshine exposure my skin needs to continue optimizing vitamin D production for preventing skin cancer.
One thing that I don't understand is why UVA is treated so "nonchalantly" for lack of a better word, when it comes to UV awareness and protection.
As you said, UV does not reduce much in the evening.
For one thing in sunscreen, as we know there is little to no indication on most sunscreens how much they protect against UVA.
But also, and this is more in response to what I'm reading here, why in the world does the UV index virtually entirely ignore UVA? How is this index so recklessly misleading?
I used to believe for many years now that at 6-7PM I don't have to wear sunscreen anymore, with the UV index being 1 or 0. When in reality that couldn't be further from the truth because UVA is still very strongly present at that time.
Where does the UV index come from? Is it simple extremely outdated or is there a reason why UVA is (still) virtually not represented in the UV index?
And is there any other way to find out until what time we have to protect ourselves from UVA other than actually buying a UVA meter?
(Thanks again for yet another very insightful post by the way)
Thanks Guys.
Stephan: You don't need to worry too much about the UVA component from a skin damage perspective. Both UVA and UVB are attenuated by the atmosphere, just more so for UVB than UVA. Although there's a lot more UVA than UVB, it's the shorter wavelength higher-energy UVB photons that cause most damage. In fact, the 'action spectrum' for skin damage decreases so steeply with wavelength that for high sun elevations, the contribution towards skin damage from UVA wavelengths is only about 5% of that from UVB wavelengths (that fraction does increase at lower sun elevations, but by then the total is in any case much smaller). I might talk about it in a later post.
Thanks Richard. Your detailed explanation of the difference in atmospheric absorption of UVA versus UVB for different elevations of the sun makes sense. It helps me plan and control the right amount of sunshine exposure my skin needs to continue optimizing vitamin D production for preventing skin cancer.
One thing that I don't understand is why UVA is treated so "nonchalantly" for lack of a better word, when it comes to UV awareness and protection.
As you said, UV does not reduce much in the evening.
For one thing in sunscreen, as we know there is little to no indication on most sunscreens how much they protect against UVA.
But also, and this is more in response to what I'm reading here, why in the world does the UV index virtually entirely ignore UVA? How is this index so recklessly misleading?
I used to believe for many years now that at 6-7PM I don't have to wear sunscreen anymore, with the UV index being 1 or 0. When in reality that couldn't be further from the truth because UVA is still very strongly present at that time.
Where does the UV index come from? Is it simple extremely outdated or is there a reason why UVA is (still) virtually not represented in the UV index?
And is there any other way to find out until what time we have to protect ourselves from UVA other than actually buying a UVA meter?
(Thanks again for yet another very insightful post by the way)
My head is spinning