1) Filters and colored lights
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
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
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
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
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.