COLOR PERCEPTION

COLOR VISION

Light from the sun is actually made up of different colors combined to form white light.

blue and green are absorbed	white light = mixture of colors

red reflected	apple appears red
Apple appears red because its surface absorbs blue and green light but reflects red

Color is a part of the human vision system. When the image of the red apple is focused at the back of the eye, it affects red sensitive cells to a greater extent. The color is then identified as red. There are also color receptor cells (cones) that are particularly sensitive to the other primary colors of light. All other colors affect these receptors to varying degrees so that we are able to discern a great range of different color mixtures.

COLOR

SPECTRUM

White Light

	Prism	Color Spectrum

A prism can be used to show that white light is really a bunch of mixed colors. Although the spectrum shows that white light contains a continuous range of colors, colors from just three areas of the spectrum could be mixed to form any other color.

These three colors of light are from parts of the spectrum that are

red,

green

and blue.

Different colors of light have different wavelengths.

SPECTRUM

The wavelength of color light is measured in nanometers.

	red
	orange
	yellow
	green
	blue
	violet

The numbers shown here are the number of nanometers between each wave of light.

How small is the distance between each wave of light? Well there are one billion nanometers in one meter. So the waves of light are extremely small, but they make all the difference in the colors that we see.

It is this difference in wavelengths of light that the human eye detects as different colors.

Note: Colors such as magenta that are not in the spectrum produced by a prism can be produced by mixing colored illumination from two or more parts of the spectrum. A pinkish-purple light that looks like magenta can be made by mixing red light and blue light.


Magenta	Orange dims to Brown

When we see a shade of brown on a television screen, it is actually a very dark shade of orange.

Spectrum colors overlap, and we see the mixed colors between. That is why we do not see a color such as magenta. It takes a mixture of red illumination and blue illumination to make magenta illumination, but red and blue are on opposite sides of the spectrum.