Common Fluorescent Sunlamps are an Inappropriate Substitute for Sunlight¶

Abstract

Fluorescent sunlamps are commonly employed as convenient sources in photobiology experiments. The ability of Kodacel to filter photobiologically irrelevant UVC wavelengths has been described. Yet there still remains a major unaddressed issue--the over representation of UVB in the output. The shortest terrestrial solar wavelengths reaching the surface are approximately 295 nm with the 295-320 nm range comprising approximately 4% of the solar UV irradiance. In Kodacel-filtered sunlamps, 47% of the UV output falls in this range. Consequently, in studies designed to understand skin photobiology after solar exposure, the use of these unfiltered sunlamps may result in misleading, or even incorrect conclusions. To demonstrate the importance of using an accurate representation of the UV portion of sunlight, the ability of different ultraviolet radiation (UVR) sources to induce the expression of a reporter gene was assayed. Unfiltered fluorescent sunlamps (FS lamps) induce optimal chloramphenicol acetyltransferase (CAT) activity at apparently low doses (10-20 J/cm2). Filtering the FS lamps with Kodacel raised the delivered dose for optimal CAT activity to 50-60 mJ/cm2. With the more solar-like UVA-340 lamps somewhat lower levels of CAT activities were induced even though the apparent delivered doses were significantly greater than for either the FS or Kodacel-filtered sunlamp (KFS lamps). When DNA from parallel-treated cells was analyzed for photoproduct formation by a radioimmuneassay, it was shown that the induction of CAT activity correlated with the level of induced photoproduct formation regardless of the source employed.

The hairless mouse in skin research

“…The wavelengths of UVR most effective in causing adverse effects on the skin of hairless mice, including sunburn, photoimmunosuppression, and skin carcinogenesis, are UVB [49-51]. Thus, most photobiology studies that employ hairless mice are carried out using UVR sources that emit UVB or mixed UVB and UVA wavelengths [52]. …”

“…UVR directly induces cyclobutane pyrimidine dimers and (6-4) photoproducts in DNA [50,52]. Exposure to UVB also indirectly induces oxidative DNA damage, in part through the ROS generated by infiltrating inflammatory cells and activated keratinocytes.…”

Sources and measurement of ultraviolet radiation

“…This may pose little problem if the object is to irradiate small areas of skin but for studies where large numbers of experimental animals or plants are to be irradiated, the limited irradiation field is a real problem. Because of this attention has turned to fluorescent lamps as sources of simulated UV [9]. One way to evaluate candidate lamps and decide which is the most appropriate approximation to sunlight is to calculate the percentage relative cumulative erythemal effectiveness (%RCEE) for a number of wavebands and to compare these values with the %RCEE values of a ''standard sun'' [10].…”

The effects of topically applied glycolic acid and salicylic acid on ultraviolet radiation-induced erythema, DNA damage and sunburn cell formation in human skin

“…It has been demonstrated that vehicles can dramatically affect the absorption and deposition of glycolic acid into the skin [6]. Further, the choice of light source has been shown to significantly affect biological responses to UV radiation [43,44]. Therefore, the use of a vehicle (cream) that closely mimics those used in consumer products and an artificial light source that closely duplicates solar radiation (sunlight) are critical factors in designing these types of studies.…”