Chapter 27 COLOR

Selective Reflection Different Materials have different natural frequencies for absorbing and emitting electromagnetic radiation. Most materials will absorb light of certain frequencies and reflect the rest. If a material absorbs most of the visible frequencies but reflects red light, the material appears to be red.

If the material reflects all visible frequencies, it will appear the same color as the color of the light that shines on it.

Selective Transmission The color of a transparent object depends on the color of the light it transmits.

Blue Glass

Mixing Colored Light Brightness frequency

By adding various amounts of Red, Green and Blue light, we can produce any color of the spectrum. See Fig. 27.10 pg. 521 Green, Blue and Red are called additive primary colors. Red+Green = Yellow Red+Blue = Magenta Green+Blue=Cyan

Red Blue Cyan yellow Green White Green yellow Cyan Red Blue

Mixing colored pigments, such as paints, does not work the same way as mixing light.

This is because the paint is composed of tiny solid particles that produce their color by selective absorption and reflection. Mixing them together just causes absorption of most of the light illuminating the pigments, which results in a dull neutral color.

Any of the primary colors can be produced by a subtraction of any two of cyan, magenta, or yellow. These are the SUBTRACTIVE PRIMARIES Transparencies

Complimentary Colors Recall that: Red + Blue = Magenta Red + Green = Yellow Blue + Green = Cyan Then: Magenta + Green = White Yellow + Blue = White Cyan +Red = White

We say that Magenta and Green are complimentary colors. When two colors added together produce white, they are complimentary colors.

Why the sky is blue N2 O2 Nitrogen and Oxygen molecules in our atmosphere scatter mostly UV and blue light. We only see the scattered blue light.

Why Sunsets Are Red Red, Orange and yellow light are transmitted further into the atmosphere than violet and blue. The sun appears redder as sunset approaches. As the layers of atmosphere get thicker, only the red survives while more of the shorter wavelengths get scattered.

Red, Orange and yellow light are transmitted further into the atmosphere than violet and blue. As the layers of atmosphere get thicker, only the red survives while more of the shorter wavelengths get scattered. The sun appears redder as sunset approaches.

Why Clouds are White H H O All wavelengths are scattered equally by small and large water vapor molecules resulting in a white cloud. H H O

Why Water is Greenish Blue Water molecules resonate in the infrared and slightly in the red. 30m Green and blue penetrate to the greatest depths.

Color and Vision End of Chapter 27