Le 15/06/2012 14:13, Invisible nous fit lire :
> I looked outside a little while ago, and observed that the sky was blue.
> 
> But when I asked POV-Ray to do some radiosity with a blue sky, the
> entire scene came out blue. Which, logically speaking, isn't surprising.
> If the sky is blue, clearly it's emitting blue light, which would result
> in everything being illuminated blue.
> 
> And yet, when I look outside, the world is /not/ tinged blue. So... WTH?

If the sky is "blue", why do you see a yellow sun ?
What happened to the sky at night so that the moon is white ?

IIRC, the blue of the sky is due to the variant IOR (vs void) of the
atmosphere for the "white" light: the blue is turned more toward the
earth (well, sooner: it might explains a bit the redish-moon eclipse).

It's not like the sky is rgb(0,0,1) (or even rgb(0,0.8,1)) but rather
more alike hsl(240, ??, 1000000) (outside the traditional rgb cube)

or in povray term, more like blue with a very high transmit colour of
white, maybe with a subtle tinct of blue inside... (which cannot be
expressed so far in the current SDL)

Strictly speaking, the sky does not emit light. It's a dispersing media
at best. Faint media, of large dimensions.


Also, do not forget the capability of the eyes to accomodate to various
intensity of light. The white-balance done with camera is needed in
professional production: the light is not always the same.

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