This model doesn't take into account time of day, but many do. But those mostly seem to do so incorrectly, as far as I can tell. They tend to use the measure of

This model doesn't take into account time of day, but many do. But those mostly seem to do so incorrectly, as far as I can tell. They tend to use the measure of "UVA/B incident on a horizontal square meter". However humans are not flat horizontal surfaces - and in fact a lot of my exposed skin is more vertical than horizontal. Therefore I think the correct measure should be "UVA/B incident on a meter-diameter sphere" or similar (where absorption from the atmosphere is the only contributor, not merely foreshortening). I was unable to identify numbers for this at all when I looked into it - does anyone know of a model that does this properly? Or just number of how much UVA/B is impacted by this?