Basic Optical Principles
Electromagnetic Spectrum and Visual Spectrum

Cosmic Rays	Wavelengths Less Than One Nanometer
Gamma Rays
X-Rays
Ultraviolet
Visible Light	Approx. 360-750 nm
Infrared
Hertzian Rays (Radar)
Radio & Television Rays
Long Electrical Oscillations	Wavelengths Measured in Thousands of Kilometers

Visible light is a form of radiant energy and is part of an overall spectrum of energy called the electromagnetic spectrum. As illustrated above, the scope of the electromagnetic spectrum is enormous. It ranges from extremely short waves such as cosmic rays measuring less than one nanometer (one billionth of a meter) in length, to radio and T.V. waves whose wave lengths measure in the thousands of kilometers. That portion of the electromagnetic spectrum to which the photosensitive receptors of the retina respond lies about in the middle of the spectrum and we call it visible light. As demonstrated above, visible light occupies only a very small portion of the overall spectrum of radiant energy. In optics we are concerned not only with the visible spectrum but also with those wave lengths immediately surrounding it which constitute ultraviolet and infrared radiation or �invisible light.� The chart on the next page amplifies the visual spectrum.

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Short Ultraviolet	200-295 nm
Long Ultraviloet	296-400nm
Visible Spectrum	390-750nm
Short Infrared	750-400 nm
Long Infrared	1400-2000nm

Waves of the visual spectrum are measured in billionths of a meter. As mentioned earlier, this unit of measurement is called a nanometer (nm). The range of the visible spectrum and its immediate surroundings is indicated above.

Color	Wavelength
Violet	380 nm
Blue	460 nm
Green	510 nm
Yellow	560 nm
Orange	610 nm
Red	650 nm

The visual spectrum can be further broken down into the various colors which are the components of �white light.�