5 replies to this topic

[mike_ag]

I have always thought UVA levels were way higher at midday (11am-3pm), like this chart seems to confirm : 

http://www.ijdvl.com...198_12512_4.jpg

 

But then I read that : 

 

" They are present with relatively equal intensity during all daylight hours throughout the year " 

source : http://www.skincance...ion/uva-and-uvb

 

I'm confused ...

Edited by mike_ag, 15 June 2016 - 10:42 AM.

[Darryl]

UVA intensity also varies by time of day and season, but the variation is less pronounced than for UVB. However the attenuation by atmospheric dust & aerosols is dwarfed by the angle of the surface to the incident sunlight.

 

Here's a sunny day in Beirut (34° N).

 

 

Here's the seasonal variation on a horizontal surface in Beirut.

 

Edited by Darryl, 15 June 2016 - 12:37 PM.

[mike_ag]

Interesting thanks ! 

 

So around 8-15 times more UVA at midday than at 4PM in your city, if I understand correctly. 

 

is there a website who offers for every city worldwide ? 

 

 

 

Edited by mike_ag, 15 June 2016 - 12:50 PM.

[Logic]

Look up Tiron here for an interesting read on 100% protection from UVA. (and B IIRC)

Edited by Logic, 15 June 2016 - 08:01 PM.

[aconita]

You don't need a chart for every city, eventually just a chart for every latitude, dusts and aerosols will vary anyway on almost a daily basis.

 

But what really matters is that those pattern you see for Beirut would be basically the same everywhere else, just the values will change but not the take home message: radiations are stronger by far between 10AM and 2PM (legal hour might slightly shift that, like 11AM-3PM) in those 4 months across the summer solstice.

[Cloomis]

Ooo! I covered this in detail in my latest blog post.

 

Basically, UVA, with it's longer wavelength, is less attenuated going through atmosphere, so UVA is less reduced in winter, morning, and afternoon than UVB.

 

More here: https://www.unaging....lth-and-beauty/