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In this section:

The Optics Book

Describing Colors
Types of media

9. Interferences & difraction
10. Polarization
11. Quantic Optics

# Colors

The different colors which we see are actually just mixtures of a few colors.  Colors can be mixed by addition (which involves the primary colors) or by subtraction (which involves the secondary colors).  The concept of color addition and subtraction may be difficult to understand because it conflicts with experience from paints.  Therefore it is important to keep in mind that the colors we talk about in physics are of a pure form whereas the paints which we use in the real world are not pure.

 Colors Credits: Karen Wu

The primary colors used in color addition are Red, Green, and Blue.  The combination of the primary colors forms white.  The color white is seen when an object reflects all color.  Red and Green mix to form yellow, Green and Blue mix to form Cyan, and Red and Blue mix to form Magenta.  The colors formed from the primary colors are known as the Secondary colors.

The color television uses the concept of color addition.  The television has millions of tiny little dots, called pixels.  Colors are seen when electron beams shine on these pixels, causing them to glow either red, green, or blue.  We see different colors on the screen depending on how the various amounts of the colored pixels are adding together.

 Secondary Colors Credits: Karen Wu

The secondary colors are Cyan, Magenta, and Yellow.  When these three are mixed together, they form black.  Color by subtraction involves the absorption of some colors and the reflection of the colors which weren’t absorbed.  The colors that are reflected, are the ones which we see.

Colors can be absorbed through the use of such things as dyes, pigments, or filters.  The color of the clothes that we wear is seen because of color subtraction.  For example, if your friend is wearing a yellow shirt, you see it as yellow because of color subtraction.  The white light hits the shirt, and the dye of the shirt absorbs the blue part of the spectrum and reflects the red and green.  You then add the red and green together and see the color yellow.