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Colored lights - color of objects

Colored lights

1) Filters and colored lights

A filter consists of a colored transparent material: light can pass through it, but its color is modified.
A red filter allows to get red light, a blue filter allows to get blue light etc.
More generally, a filter allows to obtain a light whose colore is the same as it.

White light is a mix of colored lights and a filter can only be crossed by one of them. The other colored lights are stopped. For instance, a red filter can be crossed by a red light but blue and yellow lights are stopped.

2) Primary colors

Some new colored lights can be obtained mixing several colored lights: this is the additive color synthesis.
Nevertheless there are three colors that allow to obtain all other colors.
These colors are red, green and blue: they are called primary colors.
If mixing two beams of colored lights that have the same intensities, then you can get the following colors:
- Green and blue give cyan
- Blue and red give magenta
- Green and red give yellow
If these three primary colors are mixed together they form a white light.

This additive synthesis must be distinguished from the soustractive synthesis of colors, that consists of mixing colored materials like paints made of colored pigments that absorb light.

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