Ultraviolet radiation

The ultraviolet spectrum extends from approximately 10 to 400nm, overlapping x-rays at the shorter wavelengths and running into the violet end of the visible spectrum (Figure 2). The ultraviolet spectrum is further divided into near UV (320-380nm), middle UV (200-320nm) and vacuum UV (10-200nm) by physicists, or into UVA, UVB, UVC OR UVD, by biologists. The UVA extends from 320nm to 400nm and is known as the glass transmission region, the UVB extends from 280nm to 320nm and is known as the erythemal or sunburn region, while the UVC extends from 185nm to 280nm and is known as the bacterial region. The UVB region is best known for the erythemal effects - which stimulate melanin production as a means of protection - sun tanning. The suntan was once popular as a symptom of a healthy lifestyle (Figure 3) but the dangerous effect of ultraviolet in triggering malignant melanoma of the skin is now recognized. The photographer's interest lies in the near ultraviolet, or UVA, region although the researcher should understand the effects of the other regions of ultraviolet. For example, there are two significant biological effects of ultraviolet radiation: germicidal and erythemal. Short wavelength ultraviolet is very effective as an antibacterial agent. Some caution needs to be exercised with "continuous" sources of ultraviolet, as there is a real risk of burning yourself and/or your patient, or of getting conjunctivitis. This is because the eye cannot "see" below 400nm, but the peak of erythemal activity occurs at 297nm (Figure 4); also there is no heat emission from most sources of ultraviolet to warn the photographer of harmful exposure. This is discussed further under "sources of ultraviolet radiation."

Figure 2 (above). The ultraviolet spectrum is divided into near UV (320-380nm), middle UV (200-320nm) and vacuum UV (10-200nm) by physicists, or into UVA, UVB, UVC OR UVD, by biologists.

Figure 3 (left). Sun beds are efficient sources of UVB radiation designed to stimulate melanin production - a tan - the historic symbol of a healthy lifestyle.

Figure 4 (above). The eye cannot "see" below 400nm, but the peak of erythemal activity occurs at 297nm so caution needs to be exercised with "continuous" sources of ultraviolet as there is a real risk of burning yourself and/or your patient, or of getting conjunctivitis.

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Reflected or direct ultraviolet photography >