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A shadow is caused by an object blocking light so that it doesn't reach a surface. The area in shadow appears black because there is no light falling on it -- it appears dark.

In fact, most shadows aren't totally black, because light usually bounces around the obstruction off other objects (indirect lighting). You can also get coloured shadows where there are multiple light sources of different colours. e.g. in a nightclub or disco. Translucent objects may cast coloured shadows, e.g. stained glass in a church, where only some of the light has been blocked by the window.

Outside on a sunny day, shadows may appear black because your eyes have compensated for the bright light and can't make out the detail. But if you walk into the shadow your eyes will adjust to the light, and you'll see that the shadow isn't black at all, it's just darker than in the direct sunlight.

On a bright day with a blue sky, you may also see that areas in shadow (especially white objects in shadow) appear to have a blue tint. This is because although the shadow is not directly lit by the sun, it is lit indirectly by the blue sky above. It may not be very obvious, because your eyes and brain are adept at adjusting to changes in brightness and colour, but a camera will see it clearly. If you take a picture in shadow on a sunny day it comes out looking quite cold and blue. This is why many cameras have a 'shade' mode that alters the colours to remove the blue colour cast.

To make your own coloured shadows, try experimenting with two or more torches with different coloured plastic over the bulbs. Place objects on a piece of white A4 paper (in a dark room), and move the torches around and note the effects. An example of a coloured shadow can be seen here: http://www.Flickr.com/photos/sevennine/442923580/

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17y ago

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