A comparison of the UV-B irradiance of low-intensity, full-spectrum lamps with natural sunlight
James C. Ball, PhD
There are significant risks to humans exposed to lamps that emit high intensity UV-B radiation because light in this wavelength range can cause sunburns (Armstrong et al., 1985; Berger and Urbach, 1982), cataract formation (Silney, 1983), and has been associated with the development of skin cancer (Freeman et al., 1988; Henriksen et al., 1989). For these reasons manufacturers are reluctant to sell lamp sources that emit significant amounts of UV-B light to the general public. This has led me and others to question how much UV-B radiation is actually emitted by full-spectrum lamps. Gehrmann (1987;1994) has measured the UV-B light output of a variety of commercial lamp sources and has indeed found that one of the most commonly used full-spectrum lamps (e.g. Vita-Lite®; Duro-Test) emits very little UV-B light.
There is very little experimental data on the metabolic or behavioral requirements for natural sunlight or full-spectrum light in maintaining captive reptiles and amphibians. Gehrmann et al. (1991) observed that neither vitamin D3 supplementation nor exposure to UV-B light effected the growth of the heliophilic western fence lizard (Sceloporus occidentalis). Roberts and Gehrmann (1990) compared the growth of bearded lizards (Pogona vitticeps) exposed to either plant lights (Gro-Lux®) or full-spectrum lights (Vita-Lite®). Both groups were also exposed to a black light. There were no significant differences in growth between the two groups suggesting that subtle adaptive physiological and behavioral responses were not dependent on full-spectrum light. The design of this experiment, however, did not allow for a conclusion regarding the effect of UV-B radiation since both groups were exposed to a black light. There is a report suggesting that green iguanas (Iguana iguana) cannot metabolize exogenous sources of vitamin D3 normally (Bernard et. al., 1991). These iguanas initially showed clinical signs of metabolic bone disease, but no new bone fractures were observed after exposure to an experimental UV-B emitting lamp (Sylvania 2096, 15 watt fluorescent lamp), suggesting that iguanas require UV-B light. In addition, anecdotal reports from veterinarians treating green iguanas for metabolic bone disease suggest that full-spectrum lamps are critical for the health of these lizards (Myers, 1994).
The relative intensity of UV-B radiation from different commercial lamps has been systematically studied (Gehrmann, 1987). The purpose of this paper is to compare the UV-B light output of those lamps studied by Gehrmann (1987) with the UV-B light intensity of sunlight from a variety of locations and latitudes.
Results and Discussion
The data in Table 1 shows that the most commonly used lamps do a poor job of simulating the UV-B light intensity of natural sunlight. The only lamps that come close to the intensity of natural sunlight are sunlamps, which are sometimes used to treat psoriasis. The practical interpretation of Table 1 for the maintenance of reptiles and amphibians will ultimately depend on experiments elucidating the time-integrated exposure of UV-B light necessary for the health of captive reptiles and amphibians. For example, is five minutes of equatorial sunlight sufficient for a particular species to prevent metabolic bone disease or to stimulate breeding? The answer to these questions remains until appropriate experiments are carried out. In the mean time, Table 1 can be used as a relative guide to the use of low-intensity, full-spectrum lamps in the care of reptiles and amphibians.
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Table 1. UV-B Irradiance[a]
from sunlight and commercial lamps[b]
[a] UV-B light is defined
here to be light between 290-315 nm.
Ball, James. 1995. A Comparison of the UV-B Irradiance of Low-Intensity, Full-Spectrum Lamps With Natural Sunlight. Originally published in the Bulletin of the Chicago Herpetological Society, 30(4):69-71. Reprinted here by request of the author.
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