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Old Jun 3rd 2009, 12:23 PM   #1
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Reflected light and color

Hello, I'm not sure if this is the right place as it's not quite a technical question, but I hope you guys can help me.

I have a question about a certain situation involving reflection of light and how it effects color, and it requires somewhat of an 'artistic' eye. I had a little debate about it with some friends:

Let's say we're looking at a still lake at midday, and we have a ball floating in it. Whatever it's local, actual color is, it's upper part exposed to the sun will obviously be warmer in color. But what about the reflected light in the shadow area? Is it cooler because of the blue sky (as a secondary light source) bouncing back from the water to the ball, or will it be warm because the main light source (the sun rays) is reflected?

If it were just a ball sitting on blue ground the answer would of course be the former - the blue is reflected on it from the ground. So I guess another way to put it is to ask whether the water acting as a mirror not having an actual color would change things or not?



Thanks.
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Old Jun 3rd 2009, 04:17 PM   #2
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What do you mean by the terms "warm" and "cool" light?

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Old Jun 4th 2009, 03:18 AM   #3
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I'm talking about color temperature, e.g. blue is cool and orange is warm.
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Old Jun 4th 2009, 03:56 AM   #4
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From the link you have provided the terms ''warm'" etc. are mentioned in quotes and hence do not really correspond to these terms in physics. Like a "cool" dude isn't really cool.
Light is electromagnetic radiation. When you sit in front of a campfire, you 'feel' the heat and 'see' light radiated by it. In fact even the radiated heat you feel is electromagnetic radiation in the infra red region (you may have heard of infra red lamps used for heating) which our eyes can't see but our skin can feel. The distinction between light and heat in this context is thus made by the human body.

Nature knows no such distinctions.
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Old Jun 4th 2009, 01:42 PM   #5
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Let me clarify - I didn't mean heat. What I meant was regarding the color of the light. The temperature of color as learnt by artists, and what we all learnt about the color wheel in kindergarten. How different objects reflect light onto each other and such.

In other words, to simplify matter - would the reflected light from the sun reach the lower part of the ball, or would the scattered light of the sky reflect onto it?
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Old Jun 4th 2009, 11:45 PM   #6
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From the figure the sun's rays are perpendicular to the ball (it must be noon) and these rays will go back straight up. The rays hitting the water near the ball will also go straight up and will not hit the lower side of the ball. Rays scattered by the sky (Rayleigh scattering) will be reflected in the water and these can strike the lower side of the ball. The water also can scatter light directly (Raman Scattering) .Light from such scattering can also fall on the lower side of the ball.
At times other than midday especially towards evening light from the sun can reflect directly from the water onto the lower surface of the ball.
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