Electromagnetic Spectral Ranges of Interest in Photochemistry

The photochemically active region of the electromagnetic spectrum has been divided into five sub bands the vacuum-UV (VUV), UV-C, UV-B, UV-A and VIS (Fig. 3-8). The subdivision of the UV spectral domain is mainly due to phenomenological reasons (Fig. 3-9) that are related to physical, biological or medicinal effects. The UV-B region is usually defined between X of 280 nm and 315 nm (van- 

Loon and Duffy, 2000, McCluney, 1994), or sometimes between X of 280 nm and 320 nm (Sonnemann, 1992). Other authors define it between X of 290 nm and 320 nm because no solar radiation between 280 nm and 290 nm can penetrate through the atmosphere to reach the ground level (Moore, 1996). 

Absorption of UV-C radiation by cellular constituents of organisms may lead to severe cell mutations and cell death. Therefore, this wavelength band is often called the germicidal range. It is used in UV disinfection processes to inactivate bacteria, viruses and other microorganisms (cf Chapter 9). At the Earths surface sunlight contains no VUV and UV-C radiation because of their efficient absorp- 

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