Figure 1 Diagram showing ultraviolet portion of solar spectrum.
In Figure 1 The UV portion of the spectrum is divided into UVA, UVB, and UVC. These designations are somewhat arbitrary, but they are convenient divisions for the discussion of the interaction of UV radiation with ozone and biological organisms.
The UVB and UVC radiation represents that portion of the spectrum that is capable of damaging biological organisms and is also that portion absorbed by the ozone layer above the earth. High energy UVC photons (wavelengths shorter than 290 nm) are almost completely absorbed by ozone and very few reach the earth’s surface. This is fortunate since life as we know it would not exist if this were not the case. For example, UVC radiation is emitted from “germicidal” lamps which are used to kill biological organisms. UVB radiation (wavelengths between 290 and 320 nm) is only partially absorbed by the ozone layer and can damage biological organisms while UVA (wavelengths greater than 320 nm) is not absorbed by ozone and generally is not damaging to biological organisms. These relationships will be discussed in more detail in a later section.
% of Total Energy
UV radiation, it should be noted that this represents a very small portion of the total radiation from the sun
that reaches the earth’s surface. Much is filtered out by our atmosphere. Table 1 lists the various regions
of the solar spectrum, indicating the percentage of total solar energy in each region. UV radiation
(represented by UVA, UVB, and UVC which will be defined in a following section) makes up only a little over 8% of the total. Most of the solar radiation is in the visible and infrared.