Hello Michael,
> This is probably because sunlight travels through a thicker layer of
> atmosphere, when it is 'lower' than in summer. The more atmosphere light
> passes through, the more it filters out UV.
>
> Michel van Dijk
Well, after some googling+reading, I did come across information to the
effect that UV content is affected by seasonal change and zenithal angle.
So, the more perpendicular the sun relative to the earth surface, the more
penetrating the UV radiation. And vice-versa. The only thing I wonder, now,
is when was D50 measured? I mean, in which season of the year? I'm probably
doing my measurements in the wrong time of the year to ever hope to reach
any agreement with the D50 published CIE data -- Murphy's law.
It will be interesting to see how different will the 400 to 450 nm range of
my spectral distribution change with seasons.
Color. It is never ending.
Roger Breton
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