Reading for precise information Nature of Light and Color

We know the world through our senses: sight, hearing, touch, taste, and smell. Each sense responds to particular stimulus, and the sensations we experience give us information about our surroundings. Sight is the most important of the senses. Through sight we perceive the shape, size, and color of objects, also their distance, motions, and relationships to each other. Light is the stimulus for the sense of sight - the raw material of vision.

To understand the fascinating story of light, let us explore its nature, its behavior in lenses and prisms, and then its uses in science and art.

Nature. Electromagnetic waves carry energy in all directions through the universe. All objects receive, absorb, and radiate these waves which can be pictured as electric and magnetic fields vibrating at right angles to each other and also to the direction in which the wave is travelling. Light is one form of electromagnetic wave. All electromagnetic waves travel in space at the same speed - the speed of light.

Electromagnetic waves show a continuous range of frequencies and wavelengths. Frequency is the number of wave crests passing a point in one second. Electromagnetic wave frequencies run from about one per second to over a trillion per second. For light, the frequencies are four to eight hundred trillion waves per second. The higher the frequency, the shorter the wavelength.

Visible light is that portion of the electromagnetic spectrum that normally stimulates the sense of sight. Electromagnetic waves exhibit a continuous range of frequencies and wavelengths. In the visible part of the spectrum these frequencies and wavelengths are what we see as colors. The wavelengths of light range from 3,500 A to 7,500 Å. The wavelengths of infrared rays (7,500 Å - 10,000,000 Å), longer than light rays, are not detected by the eye, and do not appreciably affect ordinary photographic film. They are also called heat or thermal rays and give us the sensation of warmth.

Light behavior includes transmission, absorption, reflection, refraction, scattering, diffraction, interference and polarization. Transmission, absorption and reflection account for all the light energy when light strikes an object. In the course of transmission, light may be scattered, refracted or polarized. It can also be polarized by reflection. The light that is not transmitted or reflected is absorbed and its energy contributes to the heat energy of the molecules of the absorbing material. The modification of light through these processes is responsible for all that we see.

Reflection is of two kinds - diffuse and regular. Diffuse reflection is the kind by which we ordinarily see objects. It gives us information about their shape, size, color and texture. Regular reflection is mirror-like. We don't see the surface of the mirror; instead, we see objects that are reflected in it. When light strikes a mirror at an angle, it is reflected at the same angle. In diffuse reflection, light leaves at many different angles. The degree of surface roughness determines the proportion of diffuse and regular reflection that occurs. Reflection from a smooth, polished surface like a mirror is mostly regular, while diffuse reflection takes place at surfaces that are rough compared with the wavelength of light. Since the wavelength of light is very small (about 5,000 Å), most reflection is diffuse.