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Optical Radiation
time:2016/8/10  View times:594

Optical Radiation 

The electromagnetic spectrum has three bands of what is termed optical radiation: UV encompasses wavelengths from 100 nm to 380 nm; visible light comprises radiation between 380 nm and 780 nm; and infrared (IR) consists of wavelengths from 780 nm to 10,000 nm (Figure 1). These can all be further divided into sub-bands. Within the UV spectrum there is UVA (315 nm to 380 nm), UVB (280 nm to 315 nm), and UVC (100 nm to 280 nm)*; the IR spectrum contains IRA (780 nm to 1,400 nm), IRB (1,400 nm to 3,000 nm), and IRC (3,000 nm to 10,000 nm); and the visible light spectrum can be generally classified as short- (blue), medium- (green), and long-wavelength (red) light.

Visible light, like all electromagnetic radiation, has energy; the amount of photon energy is a function of wavelength, with shorter wavelengths being most energetic. Thus, blue-violet light is the highest-energy band of the visible spectrum.

Light Absorption in the Eye Visual perception occurs when light strikes the retina, an intricate structure of highly specialized cells that form the innermost layer of the globe. Before reaching the retina, incoming light must penetrate the ocular media, the transparent tissues and fluids that lie between the front of the eye and the retina. The ocular media—consisting of the cornea, aqueous humor, lens, and vitreous humor—either absorb or transmit light, depending on its wavelength. 

Figure 1. The electromagnetic spectrum and optical radiation

Almost all of the UV that reaches the eye is absorbed by the cornea or the crystalline lens, so that in adult eyes only 1% to 2% of incoming UV is transmitted to the retina.3 The cornea and crystalline lens also block IR above 980 nm; and the vitreous absorbs the IR above 1400 nm that is not absorbed by the lens. The net result of light filtering by the ocular media is that the retina is exposed almost exclusively to the visible portion of the solar spectrum (Figure 2).

Figure 2. Absorption and transmission of solar radiation in the

eye. The cornea and crystalline lens filter out UVB and most

UVA, so that the most energetic light reaching the retina is short

wavelength blue-violet light.

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