The efficacy of photochemical interaction per incident quantum and the photobiological effects per unit radiant exposure typically vary widely with wavelength. The number of altered molecules produced relative to the number of absorbed photons is referred to as the ‘quantum yield’ ( Phillips, 1983). A wavelength of 10 nm corresponds to a photon energy of 124 eV, and 400 nm to an energy of 3.1 eV ( WHO, 1979). The photon energy is generally expressed in terms of electron volts (eV). In any photochemical interaction, the energy of the individual photon is important, since this must be sufficient to alter a molecular bond.

The German Industrial Standard (DIN 5031) defines UVA as radiation between 315 and 380 nm ( Mutzhas, 1986).įrom the viewpoint of photochemistry and photobiology, interactions of optical radiation with matter are considered to occur when one photon interacts with one molecule to produce a photochemically altered molecule or two dissociated molecules ( Phillips, 1983 Smith, 1989). The reader should also be alerted to the fact that the CIE nomenclature is not always followed rigorously and that some authors introduce slight variations for example, distinguishing between UVB and UVA at 320 rather than 315 nm (frequently used in the USA) and defining UVC as 200–280 nm ( Moseley, 1988). It is important to recognize that these spectral band designations are merely short-hand notations and cannot be considered to designate fine dividing lines below which an effect is present and above which it does not occur. Visible light is the region between 400 nm and 780 nm. Some spectral designations are based on uses, e.g., ‘germicidal’ and ‘black-light’ regions.įor the purposes of this monograph, the photobiological designations of the Commission Internationale de l'Eclairage (CIE, International Commission on Illumination) are the most relevant and are used throughout to define the approximate spectral regions in which certain biological absorption properties and biological interaction mechanisms may dominate ( Commission Internationale de l'Eclairage, 1987). Meteorological scientists typically define optical spectral regions on the basis of atmospheric windows. In one optical convention, shown in Figure 1, UVR is divided into vacuum UV, extending from 10 to 180 nm middle UV, from 180 nm to 300 nm and near UV, from 300 nm to 380 or 400 nm. For example, in optics, it is convenient to separate the spectrum into different bands on the basis of the transmission and absorption properties of optical materials (e.g., glass and quartz).

It is important to recognize that no single convention is uniquely ‘correct’ but that each may be useful for a particular branch of science and technology. The optical radiation spectrum is generally considered to fall between 10 nm and 1 mm, and several different conventions have been developed to describe different bands within this spectrum. Electromagnetic spectrum with enlargement of ultraviolet (UN) region

Acdc band radiant energy examples