Physics Question #312

Andrew Hickey, a 13 year old male from the Internet asks on December 19, 1997,

Why do wet objects shine?

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The answer

Brian Funt answered on December 19, 1997

The glare is the colour of the light from the light bulb or sun and not the colour of the object. So the light coming from a wet object has a portion with the colour of the object and a portion with the colour of the white light. The white part is what makes it look shiny.

A wet object often has glare, because the water reflects a lot of the light hitting it. Some of the light of course goes through the water to the object and then back out through the water into the air and to your eye. When the object is dry, all the light hits the object and then comes directly back to your eye. When then object is wet, you see the light bouncing off the water as a shiny glare. There are other effects other than 'shine' that wetness will create. The main one is that the object's colours will look purer. For example a pale blue will look a deeper blue colour. Another term for a 'pure' colour is to say that it is a 'saturated' colour. The reason that the colours become more pure/saturated is a bit more complicated than the shiny glare. It has to do with what is called internal reflection within the water layer. The internal reflection means that the light first comes through the water, hits the object and then goes back into the water. However, some of the light won't leave the water, but will instead be reflected back down to the object again. This can happen several times. If the object is bluish, then the light bouncing off the object will be bluish. When it then hits the object a second time after having been reflected back by the water, it will be blue light hitting the blue object, which will result in even bluer light.

This increase in colour purity/saturation is the reason that you usually get photographs with a glossy finish. The gloss acts like the water and makes the colours look richer.

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