Total UV output of lamps
The following table lists time to accumulate the dose of 50 J/m2 of UV irradiation for each lamp used in this study. Irradiances are listed in UVA, UVB and UVC ranges. Total irradiance is also included. (For further details, see the main article.) Please also note the data of Active UVHeat measured at a distance of 1.5 meters, that was not listed in the original study.
The calculation of dose is based on Erythema Reference Action Spectrum as specified in joint ISO/CIE standard ISO 17166:1999 / CIE S 007/E-1998.
ICNIRP (International Commission on Non-Ionizing Radiation Protection) has issued a recommendation1) with a limit of 30 J/m2 for 8 hour exposure to eye or skin. The limit is set as a "desirable goal" for the most sensitive, non-pathologic, skin phototypes known as “melano-compromised”. It is further stated: "The limits represent conditions under which it is expected that nearly all individuals may be repeatedly exposed without acute adverse effects and, based upon best available evidence, without noticeable risk of delayed effects."
Due to the fact that the said limit is set according to a kind of "worst case scenario" - and the fact that a more lenient daily limit of 50 J/m2 has been adopted in the finnish legislation - the time to obtain 50 J/m2 dose is listed in the following table. This would broadly represent the sensitivity of skin types II or III (darker and/or tanned), which are less sensitive and are probably most common among the general public wordwide.
It should be noted, that the previously often used, but no longer recommended reference MED is 200 J/m2. (MED = Minimal Erythemal Dose, the dose that would cause first symptoms of sun burn, i.e. reddening of skin.)
The recommended daily exposure limit is listed here to enable reptile keepers to evaluate the possible risks caused by extended exposure to the unshielded light from their terrarium lamps. One can immediately see, that in comparison to natural sunlight, the lamps are still quite weak. New data obtained recently also suggest, that the sun's measurement here may show too low values, because the sensitivity of the spectroradiometer have had to be reduced to accommodate the strong irradiation from the sun. A measurement on May 31 1997 at noon by the Radiation and Nuclear Safety Authority of Finland (Lasse Ylianttila, pers. comm.) gives approximately 60% higher D3 Yield Index and only 7.3 minutes to reach 50 J/m2 dose. The measurement was done with a different device, so a direct comparison is not valid. It should be further noted, that the said recommendation is not intended to limit people's exposure to natural sunlight. Its main concern are artificial UV sources.
While with most lamps the time to reach doses considered risky to human eyes or sensitive skin is fairly long, with some of the lamps the recommended limit is reached in less than an hour. It is conceivable, that such a time period is accumulated within a close distance from the terrarium lamp e.g. during cleaning procedures or maintenance. Also if lamps are installed in such a configuration that the light can enter unfiltered in the human living area, unconditioned people, like small children, might be at risk.
With this new data available, anything that was said in section "Health hazard of UV irradiation" as a warning in conjunction with Active UVHeat, will apply to other high output lamps as well.
With this in mind, when any high output lamp is utilised, adquate shielding is important. The terrarium should also have a shaded area available to all animals at all times, to allow them to photoregulate at will.
There is a valid argument, that the reptiles whose natural habitat is in subtropics or even desert, are naturally acclimatized to the strong UV irradiation from the sun and therefore the caucasian human limits should not apply to them. On the other hand, the very same pigment (or any other type of protection) that enable the animal to thrive in such conditions, will simultaneously decrease the capability of the skin of such animal to photosynthesise 7-DHC to Previtamin D3 and thus reduce the amount of vitamin D3 available to that animal. It would therefore require far stronger UVB irradiation to photosynthesise required amount of vitamin D3 in its skin - which would again be more harmful by the same factor. In this sense, exceedingly high UV content may not be desirable in all cases. Especially when the UV source is not associated with heat, as is the case with "cold" fluorescent lamps, the unnatural condition may hinder animals' capability to regulate its exposure.
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