why doesn't sunlight look "warmer" than incandescent

[electricpete]

I was playing with the dimmer switch in my house. When I turn it very low the white light turns toward yellow and then orangish before it goes out. I think about my Plank's curve and it makes some sense. Perhaps at full current / full temperature the peak is near the center of the visible band and we get all frequencies giving whitish light. As temperatue of the filament decreases the peak goes to longer wavelengths and most of the energy shifts toward the red. So far so good. Makes sense to me. (sound right to you?).

But now what about the sun. I read the sun is around 6000C and lightbulb filament around 3000C. So sunlight should have a peak even more toward the bluish end of the spectrum than a lightbulb, but if anything I perceive the opposite.. sunlight seems a little bit yellow compared to a lightbulb.

So what gives. Is attenuation of the high frequencies part of it? If so does sunlight look less yellow and more blue in outer space?

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[ogi]

Maybe thats why the sky is blue.

 

[eyec]

there is no atmosphere in a lightbulb - unles you make your own using candles and maybe some wine and soft music

 

[IRstuff]

The answer, at least, in my mind, is you ;-)

Color perception is a subjective thing, compounded by the fact that the eye/brain processing can modify the color balance. Supposedly, your color perception includes the ability to strip out a certain amount of color bias, such as when the sun is low in the sky, colors are perceived without a reddish/orange bias. Therefore, when the sun is viewed in a blue sky, your brain removes some blue from the sun, pushing it back towards yellow.

If you use something like unpolished alumina or barium sulfate or any other "white" reflectance standard and view the reflection of sunlight on it with a neutral background, you'll get white. Don't use office paper, since they contain "brighteners" to force whiteness under office lighting.

Conversely, you could try to view your halogen source under the same sky conditions as when you perceive a yellow sun and see what that gets you.

Note that the sun usually looks quite white when reflected from cumulus clouds or directly, under partly cloudy conditions. My white venetian blinds look white in sunlight.

TTFN

 

[electricpete]

Why is the sky blue - I think I know that one. The blue end of the spectrum interacts with the atmosphere much more and therefore blue light fron the sun is more likely to be reflected towards us by the atmosphere.

irstuff mentioned differences with sun high in sky and on the horizon. When on the horizon surely it is more toward yellow/orange, right? In that case are we again talking about more attenuation due to traveling through more atmosphere and possibly water vapor?

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[eyec]

don't forget dust & dirt particles in the atmosphere