Colour and Vision

Color and vision

The ordinary light is composed of electromagnetic radiation of varying wavelength. On the basis of wavelength of light, the electromagnetic radiation can be divided into three types which are as follows:

Range of wave length of light (˚A) Part of time
1000 – 4000 Ultraviolet
4000 – 7500 Visible part (White light)
7500 – 1000000 Infra – red

Since our eyes are sensitive only to the electromagnetic radiation of wavelengths 4000 – 7500 ˚A., it is this region which produces a definite color in a particular substance. The UV radiation (wave length more than 7500 A) are not visible to human eyes.

When white light falls on a substance the color is obtained in different ways as:
• When the white light is reflected completely the substance will appear white.
• When the white light is absorbed completely the substance will appear black.
• When all the wavelengths of white light is absorbed except one single narrow bond which is reflected. Then the color of the substance will correspond to the color of the reflected band of light.
• When only a single bond of white light is absorbed the substance will have the complimentary color of the absorbed band of the light e.g. If the color absorbed lies in the range 4000 – 4350˚A. Then the color absorbed is violet and so the complementary color obtained will be yellow green.