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National Radiation Laboratory |
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Publications
Information Sheet No. 10
May 1999
This publication can be downloaded as a PDF (41 kB)
Ultraviolet Radiation
Introduction
Ultraviolet (UV) radiation is a form of electromagnetic radiation with wavelengths between the blue region of the visible spectrum and the x-ray region.
The International Commission on Illumination (CIE) has divided the wavelengths between 400 and 100 nanometres (nm) into 3 regions:
| Region | Wavelength |
|---|---|
| UVA (near UV) | 315-400 nm |
| UVB (middle UV) | 280-315 nm |
| UVC (far UV) | 100-280 nm |
For wavelengths below about 180 nm ultraviolet is strongly absorbed in both air and water, and this wavelength region is referred to as the vacuum UV.
Ultraviolet sources and applications
The most common exposure to UV radiation, for most people, is from the sun. The sun emits a wide range of electromagnetic radiation, most of which is absorbed in the atmosphere. However, some UVB and most UVA does reach the earth’s surface.
UV radiation is produced generally either by the heating of a material to incandescence or by the excitation of a gas discharge. The emission spectrum of gas discharge tubes, eg, mercury vapour lamps, is a line spectrum at low gas pressures but the lines broaden and form a continuum at medium and high gas pressures. Low pressure mercury discharge lamps producing most of the radiation at 254 nm are commonly used for germicidal purposes.
Electric arc welding is a common source of UV radiation. The arc operates by the passage of a large current across an air gap between two electrodes.
"Black-light" fluorescent lamps are commonly used to produce fluorescence in many substances. These lamps are usually low pressure mercury arcs which have the inner wall of the lamp coated with a phosphor (cerium-activated calcium phosphate). The phosphor emits in a broad band around 365 nm.
Biological effects
The biological effects of exposure to ultraviolet radiation are dependent on the wavelength range of the radiation. As the penetration of the radiation is small, effects are mainly limited to the surface of the eyes and unprotected skin.
(a) Effects on eyes
The principal effect of excessive UV exposure is kerato-conjunctivitis which is known colloquially as "arc-eye", "welder’s flash" and "snow blindness". The symptoms are pain, discomfort similar to that resulting from grit in the eyes, an aversion to bright light, and the cornea and conjunctiva show inflammatory changes. The severity of kerato-conjunctivitis depends on the duration, intensity and wavelength of the ultraviolet radiation exposure, with the symptoms tending to disappear after about 36 hours. The maximum effect on the cornea for a given exposure is produced at a wavelength of about 270 nm, while UVA is about 1000 times less effective at producing a response.
UVA (black-light) radiation penetrates beyond the cornea but its absorption in the aqueous humour and in the lens itself produces a harmless transient fluorescence during exposure. Absorption of UVA in the lens probably contributes to its progressive yellowing with increasing age and may be a factor in producing cataracts.
(b) Effects on skin
The effects on the skin of excessive exposure will be familiar to most people as sunburn. The erythema (redness) caused by dilation of blood vessels under the skin is produced mainly by radiation of wavelengths shorter than 315 nm (ie, UVB), the wavelength of maximum sensitivity being about 297 nm. As with kerato-conjunctivitis, the severity of effect depends on the duration and intensity of the exposure and also on the skin pigmentation of the individual. Exposure promotes tanning and thickening of the skin, both of which responses increase protection. Chronic effects of repeated exposures to solar radiation include premature skin aging and skin cancer. As with erythema the most important wavelengths appear to be those below 315 nm.
Ozone production
Short wavelength UV (principally at wavelengths less than 220 nm) produces ozone by photochemical reaction with oxygen in air. The hazards from ozone from intense short wavelength sources may be avoided by ensuring adequate ventilation.
Protection and recommended limits
There is no New Zealand standard or legislation prescribing maximum permissible exposures to ultraviolet radiation. The National Radiation Laboratory assesses and advises on hazards to health presented by ultraviolet sources. The advice is based on guidelines published by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). These guidelines are based on experimental data on the effectiveness of different wavelengths of UV at producing photokeratitis and erythema. Compliance with them will protect the average individual from acute effects. Recommendations for protection from solar UV can be obtained from local Cancer Society groups or the NRL.
For further information, contact:
National Radiation Laboratory
P O Box 25099
Christchurch
New Zealand
- Phone:
- + 64 3 366 5059
- Fax:
- + 64 3 366 1156
- Internet:
- http://www.nrl.moh.govt.nz