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Tinted Lens

THE ELECTROMAGNETIC SPECTRUM
The electromagnetic spectrum is a fast gamut of radiations which include
Cosmic rays, Gamma rays, X-rays, Ultraviolet rays, Visible light, Infrared
rays, Radiowaves and so on. The classification is based on their wavelengths.
In ophthalmic optics, we are concerned with a relatively narrow band of
the electro-magnetic spectrum. The wavelengths in this region are extremely
short and are expressed in nanometers (nm). This is the unit of wavelength
and is one thousand millionth part of a meter or one millionth part of a
millimeter.

Fig. 7.1: Electromagnetic spectrum
The visible spectrum gives rise to the sensation of light. It extends from
about 380 nm to 780 nm. Various wavebands within this region are
associated with different colour sensations. For example, a light of 650 nm
gives rise to the sensation of red, 480 nm describes a blue light, and 580 nm
describes a light having yellow hue.
The radiations emitted by most sources of light and heat, whether
natural or artificial, not only include all the wavelengths of the visible
spectrum but also extend into the neighboring region, i.e., the ultraviolet
and infrared. Although, not perceived as light, these radiations are capable