[gArGOyLe^]

If theres a blue object and a yellow light shines on it.. What will it appear like? green?

Also are there any special rules? What colored object turns what color at night when bathed in artificial colored light?

here is a quote from http://www.angelfire.com/ar/rogerart/color6.html :

[phox3z]

I don't think it would...
Yellow light is made up of green and blue light (I think). The blue light would reflect of the blue object and you'd see it as... Blue!!!

Street lamps don't give off red light so anything red looks black...

correct me if I'm wrong.
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[Novacaptain]

what Foxes said...
here's a diagram of how i would imagine it. But this would be in an ideal physical model. In truth you'd probably never seee this happen. Because there would be some specular bounce-off of green too. Besides this, there's ambient light that could add an extra color to the system ( that is if you're able to get perfectly yellow light).


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[Ian Jones]

Yeah, what those guys said sounds pretty logical. Perhaps the shadow of a blue object under a yellow light may having a radiosty effect, so that the yellow of the light and the bluish shadow (Blue because of the object reflecting ambient blue into its own shadow, thats radiosity) may mix a teeny bit in the shadow and perhaps on the soft edges of the shadow. This may or may not be an optical illusion though... I'm not really sure. Just throwing an idea into the discussion.

If the blue object were reflective (all objects reflect light in some way or another) and particularily smooth and shiny then you would get a very clear and crisp highlight which would in fact be a reflection of the light source. Any highlight is a reflection of a lightsource, we tend to think of shading an object in terms of how light or dark its local colour is under the light source. What you should really be taking into consideration is that an object is a slave of its environment and lightsource/s and should be considered as part of the whole system rather than on its own. The word 'highlight' is a bit misleading. The blurriest reflection seems to be generally called a highlight on a diffuse surface, but when we start talking about a shiny chrome sphere we start calling it a reflection instead of a highlight. See my point?

So wheres the line between the two terms? I think all should be considered like a physical simulation of light and therefore a reflection or raytracing process of thought... thinking about the environment and lightsource just like phox3z and gArGOyLe^ did and considering it in a scientific way. This would of course be far more appropriate if you were going for a realistic image and is by no means the only way of approaching art. Maybe you could try an impressionistic approach to solving the problem, if that were your style.

I tried to make sense of that, but maybe I jarbled it up a bit. I have trouble getting my words across.

[Frog]

What you may not realise is that we often look at coloured lightsources, and our brain tends to adjust for this. So even under a yellow lightsource our brain will still perceive an object as blue by mentally shifting the white point. Typical household lights give off a very yellow/orange light, but we filter it out and still somehow see things in their natural colours. You can see this very clearly when you are outside and looking in to a house, the windows glow orange when the lights are on. A camera loaded with daylight balanced film will also reveal just how tinted the lightsource is.

Antoher thing to note is that the colour of the sun changes during the course of the day, it is white at it's zenith but nearer the horizon the light becomes increasingly red. The weather conditions also have a very strong effect on the colour of shadows, with blue skies producing very strong blues, while overcast skies neutralise colours.

Impressionist painters were excellent at depicting the colour of light, particularly Monet. They used shadows with colours that looked exaggerated but were in fact quite accurate to reflect the fill light from the sky or from foliage etc. The best way to begin to understand all of this is to observe reality as it is presented to you everyday, try to see how the world around you reacts to light.
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[IO_Error]

Wait a second here....

Red and Green Light would combine to make yellow, not Blue and Green.
Imagine the spectrum created by a prism, or a rainbow, and where your 3 additive primaries fall. RED - Orange - Yellow - GREEN - aqua - BLUE - violet.. I realize color names are quite arbitrary, and I have no images to illustrate, but try it in photoshop. Go to your Color tab, RGB mode, and push the R and G sliders all the way up.

-Happy Pixel Pushing!
-IO_error

[Blind Tree Frog]

[gArGOyLe^]

Thanks for the replies everyone.

I was just wondering because I had a tiny blue chair.. and when there were electricity outages and we were in candle light.. it always used to appear greenish.. not blue at all.. i'm not sure why :-/

then when I go outside at night and I try to observe colors and stuff it was pretty hard to correctly identify the colors sometimes..

The whole physics thing is very use ful.. thanks for the diagrams.. a great reminder of my high school physics classes ..

The post about radiosity and the texture and reflectiveness of color was great too..

I did not consciously realize that the brain shifts the white point.. I obsered that this morning.. very cool .. impressionist paintings are great for color study.. that painting with the hay stacks where the warm light is giving bluish cool shadows really helped understanding some things!

oh.. REd and green make yellow.. so... if red hits red and green hit a blue object.. what would get reflected? both of them? eek.. I guess more green.. because thats what I think I saw