Protecting Workers from Ultraviolet Radiation - icnirp

2. Characteristics of UVR
2.1 Basic Concepts
Protecting Workers from Ultraviolet Radiation
Ultraviolet radiation, like visible radiation (light) and infrared radiation, is radiant energy.
Together, these forms of radiant energy are referred to as “optical radiation.” Light and other
forms of optical radiation are distinguished from each other by their wavelength (the distance
between crests in the wave that carries the energy). In the optical spectrum, wavelengths are
normally quantified in terms of nanometers (1 nm = 10 –9 m) in the UVR and visible spectrum
and in terms of micrometers (1 µm = 10 -6 m) in the infrared spectrum. Light is of shorter
wavelengths than infrared and UVR is of shorter wavelengths than light. Figure 1 shows the
spectral band designations by wavelength for the optical spectrum. In describing the biological
effects of optical radiation, the spectrum is frequently divided into seven photobiological spectral
bands (CIE 1999). The ultraviolet spectral bands are: UVC (100-280 nm), UVB (280-315 nm),
and UVA (315-400 nm). The Sun and artificial light sources emit radiant energy within the
optical spectrum, comprising the ultraviolet, visible and infrared (Figure 1).
Figure 1. The electromagnetic spectrum and the wavelength bands.
The measurement of optical radiation is referred to as “radiometry.” There are a number of
radiometric terms that are used. The “radiant power” in watts (W) describes the rate of energy
output of an optical source (rather than the photometric quantity of luminous flux in lumens
weighted for the sensitivity of the eye that describes the output of a visible lamp designed for
lighting). For a pulsed optical source such as a flashlamp, the “radiant energy” in joules (J)
describes the output where one joule is equivalent to one watt delivered over 1 second or 1 wattsecond.
Two dosimetric quantities quantify human exposure to UVR: “irradiance” and “radiant
exposure.” The irradiance is the rate of surface exposure in watts per square meter (W m -2 ) and
the radiant exposure is the radiant energy per unit area accumulated over a time interval in joules
per square meter (J m -2 ).
2.2 Solar Radiation
Sunlight has played a critical role in the development of life on Earth. The infrared and visible
regions of the solar radiation comprise 95 % of the total radiation reaching the Earth’s surface.
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