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COMMENTS
On SCHEER Preliminary Opinion on
Biological effects of UVC radiation relevant to health with particular
reference to UVC lamps
Submitted by Ekaterina Mirkova
Specific comments
3. DEFINITION AND USE OF UVC DEVICES
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3.1 Definition of UVR and physical properties
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Paragraphs 5 – 7, page 15
World Health Organization Public Health and the Environment
Geneva ,2006 Environmental Burden of Disease Series, No. 13. Solar Ultraviolet
Radiation. Global burden of disease from solar ultraviolet radiation
Definition of the risk factor
Ultraviolet radiation is part of the spectrum of electromagnetic radiation emitted by the sun. It
is arbitrarily divided into three bands of different wavelength although the exact wavelength
at which the divisions are made differ for different disciplines (5). The divisions first
proposed by the Second International Congress on Light in 1932 were as follows:
UVA 400-315nm
UVB 315-280nm
UVC 280-100nm
However, environmental and dermatological photobiologists commonly use slightly different
divisions, more closely associated with the biological effect of the different wavelengths. That
is:
UVA 400-320nm
UVB 320-290nm
UVC 290-200nm
UVC is totally absorbed by atmospheric ozone, has minimal penetration to the surface of the
Earth and thus has little effect on human health. 90% or more of UVB is absorbed by
atmospheric ozone, while UVA passes through the atmosphere with little change. Thus,
the solar ultraviolet radiation of importance to human health consists of UVA and UVB.
While UVA penetrates the human skin more deeply than UVB, action spectra for biological
responses indicate that it is radiation in the UVB range that is absorbed by DNA – subsequent
damage to DNA appears to be a key factor in the initiation of the carcinogenic process in skin
The effect of solar radiation on human health depends on the amount and type of radiation
impinging on the body. This in turn depends on, firstly, the concentration of atmospheric
ozone that is available to absorb ultraviolet radiation, particularly UVB. Next, the amount and
spectral structure of radiation reaching the body is dependent on the angle at which the sun’s
rays pass through the atmosphere – at low latitudes (closer to the equator) there is more
intense solar UVR with a greater proportion of shorter wavelengths, related to the low angle
of incidence of the incoming radiation. This strongly influences biological activity.
Increasing altitude increases UVR intensity by decreasing the air mass through which solar
radiation must pass. Similarly, time of day and season as well as presence of clouds, dust,
haze and various organic compounds can alter the intensity of incident solar radiation.
Variations in cloud cover usually reduce ground level UVR, although this effect is highly
variable, depending on the characteristics of the cloud itself. Indeed, cloud cover can result in
increased ground level UVR if both direct sunlight and light scattered from clouds, reach the
earth’s surface..
INTERNATIONAL COMMISSION ON NON‐IONIZING RADIATION PROTECTION
ICNIRP PUBLICATION. ICNIRP STATEMENT ON PROTECTION OF WORKERS AGAINST
ULTRAVIOLET RADIATION
PUBLISHED IN: HEALTH PHYSICS 99(1):66‐87; 2010
BACKGROUND
UVR comprises the shorter wavelengths, highest photon energy, of the part of the spectrum
that is classified as optical radiation. The spectrum of UVR extends between ionizing soft x
rays and visible radiation.
Effects of UVR share some aspects of effects of ionizing radiation, e.g., a direct photon effect
upon DNA. The UVR spectrum is frequently divided into three photobiological spectral bands
(CIE 1987) (Fig. 1).
Fig. 1. The ultraviolet spectrum and the wavelength bands.
The Commission International de L’Eclairage (CIE) designated UVR spectral bands are UVC (100–280 nm), UV-B (280–315 nm), and UV-A (315–400 nm). Terrestrial solar UVR
consists mainly of UV-A and UV-B radiation. Only artificial light sources emit radiant energy
within the UV-C spectral band. The dosimetry of UVR exposure of the eye and skin requires
the use of several radiometric quantities and units. The irradiance (W m_2) is the surface
exposure dose rate in watts per
square meter, and the radiant exposure (J m_2) is the accumulated radiant energy per unit area
in joules per square meter.
The radiant power (W) is the rate of energy output of an optical source (W _ J s_1). The
related photometric quantity luminous flux (lm) describes the rate of energy output of a light
source weighted for the sensitivity of the eye, thus related to the visual perception associated
with a defined radiant power. For a pulsed light source such as a flash lamp, the “radiant
energy” in joules (J) describes the energy output, 1 J corresponding to 1 watt delivered
over 1 s or 1 watt-second.