BASIC CONCEPTS OF RADIATION - Environmental UV Radiation: Impact on Ecosystems and Human Health and Predictive Models - page 6

electrons. Examples of ionizing radiation include: X rays and gamma rays. Non-ionizing
radiation includes optical radiation (ultraviolet, visible and infrared radiation) and radio-
frequency radiation. The optical spectrum is frequently broken into smaller spectral
bands. The band definitions depend upon whether one is interested in optical
engineering, meteorological optics, photobiology or some other technical area. The
division of ultraviolet spectrum by optical engineers could be divided by the
transmission characteristics of soft glass materials (330-400 nm), quartz optics (middle
ultraviolet: 180-320 nm) and the absence of transmission in quartz and air (far
ultraviolet or vacuum ultraviolet at wavelengths below 180 nm). From the standpoint of
meteorological optics, the bands are defined relative to the transmission of water bands
in the infrared and ozone in the ultraviolet. However, from the standpoint of the
photobiologist, the absorbance and transmission bands of proteins and water are critical.
Thus, it is important always to define what is meant by terms such as “near ultraviolet”
or far “ultraviolet. When considering photobiological effects, it is useful to employ the
convention of the International Commission on Illumination (CIE) for spectral bands.
The CIE has designated 315 to 400 nm as UV-A, 280 to 315 nm as UV-B, and
100-280 nm as UV-C (CIE, 1987). Light (visible radiation) overlaps the UV-A and
IR-A extending from 380 nm to at least 780 nm. 1 [IR-A extends from 770 nm to 1400
nm; IR-B, from 1400 to 3000 nm; and IR-C from 3000 nm to 1 mm.] The CIE
photobiological bands are summarized in Table 1.

Table 1 . CIE Photobiological Spectral Bands

CIE Spectral
Band Designation

Wavelength Interval Characteristics

UV-C 100 nm - 280 nm Superficial absorption in tissue; significant protein

absorption, particularly at 250-280 nm

UV-B 280 nm - 315 nm Penetrates, still actinic, most photocarcinogenic

UV-A 315 nm - 400 nm Deeper penetration, less absorption; single photons

generally do not interact except in photodynamic role

Light (visible) 380 nm - 780 nm Photopic (day) and Scotopic (night) vision

IR-A 780 nm - 1400 nm Deeply penetrating, water transmits

IR-B 1400 nm - 3000 nm

(1.4 µm - 3.0 µm)

Water strongly absorbs, very slight penetration—generally
to less than ~ 1 mm

IR-C 3 µm - 1,000 µm

(1 mm or 300 GHz)

Very superficial absorption, generally less than 0.1 mm