These results verify that CFLs may emit low levels of UVR. While our lamp sampling was intentionally biased toward covered or shielding lamps, our findings clearly indicate that among these types of CFLs, there is a great deal of variation in the actual level of biologically effective UVR emitted and the resulting exposure hazard. Assuming 8 h of exposure per day, the dose of total UV ranged from 0.1 to 625 mJ cm−2 day−1, while the UVB dose ranged from 0.01 to 15 mJ cm−2 day−1.
This variability is in part a result of differences in the composition of the outer coverings. We found bulbs with plastic outer coverings at both ends of our range of UV emission, with glass enclosed and bare compact fluorescent bulbs mixed in between. Common window glass blocks UVC, UVB and some UVA2, whereas very pure quartz-type glasses are essentially UV transparent. Likewise, clear plastics such as polycarbonate are effectively opaque to UV, while acrylics may be highly transparent to UV. Some types of coverings may be composed of materials that yellow with use. We did not attempt to evaluate such spectral degradation as a function of lamp ageing or potential lot or batch variation within any individual lamp product.
Our results did not clearly indicate that covered bulbs consistently pose lower UV hazards than uncovered bulbs, in contrast to Khazova and O’Hagan’s report (11
). There were several covered bulbs among our sampling with higher irradiance and effective irradiance than the limited number of uncovered bulbs we examined, particularly the uncovered n:vision Daylight ( and ).
In general, however, the light bulbs emitted very low levels of UVR. This degree of UVR exposure is not expected to cause erythema, which is often used as a general index of UV hazard, in normal individuals with intact skin repair processes. However, these same repair mechanisms are deficient or impaired in photosensitive individuals. Similarly, accumulation of very low level photocarcinogenic exposure, as represented by our NMSC hazard weighting, is obviously of greater consequence in XP patients with known propensity to skin cancers. The question thus remains as to whether or not this level of UVR is clinically significant for photosensitive patients.
There are only a handful of studies that have evaluated the effects of UVR in doses as low as those measured here. In 2000, Runger et al.
exposed Epstein–Barr virus-transformed lymphoblasts to varying doses of UVR. They found that a single dose of 3 mJ cm−2
of UVB (280–320 nm) could elicit DNA damage in normal donor cells and inhibit growth and stimulate apoptosis in XP donor cells (19
). However, they irradiated monolayers of cells in culture, which lack the protection of skin and connective tissue that humans possess. These layers both attenuate and spectrally modify incoming radiation, which affords some protection to the underlying cells. Moreover, transformed lymphoblasts do not necessarily behave like normal cells in vitro
, further complicating any direct comparison. Thus, while the data are suggestive of risk to photosensitive patients, it is difficult to extrapolate the extent of the danger.
A more direct comparison was made by De Gruijl et al.
, who irradiated albino hairless mice with broad-spectrum UVR (~280–360) on a daily basis. A range of doses was tested, the lowest of which was 5.7 mJ cm−2
. The primary endpoint was tumor formation, which approached 100% regardless of the dose of UVR administered. Of note, the amount of time needed to reach this prevalence increased as the dose decreased (20
Kaidbey et al.
performed similar experiments with humans, looking at the primary endpoint of erythema after 5 days of repeated exposure to UVR. He determined spectrum-specific threshold doses, at which little to no erythema developed; for UVA (320–410 nm), this dose was 3.8 J cm−2
, for UVB (270–320) it was 4.7 mJ cm−2
and for UVC it was 6.5 mJ cm−2
). These results provide a rough estimate of the upper limit of acceptable UV exposure; however, they might underestimate the risk to photosensitive patients for a number of reasons. First, these experiments were performed on healthy subjects, and it is possible that lupus patients and certainly XP patients would have reacted more intensely. Second, the subjects were only followed for 5 days, whereas the average patient is exposed to bulbs for many years. It is conceivable that erythema would have developed at these doses if the exposure was sustained for longer. It is also difficult to make a direct comparison between these results and the irradiance measured in this study. The spectroradiometer used here is far more sensitive than the broadband radiometer used in the Kaidbey study. Moreover, the source they used to irradiate with UVB extended into the UVA range, which might have influenced the results.
It is also important to recognize that although the level of UV emitted from bulbs is much lower than that of the sun, patients spend considerably more time exposed to lamps than they do outdoors. This has the potential to lead to significant cumulative damage. Damage is able to accumulate when the skin does not have adequate time to recover from the initial insult, which usually takes 24–48 h (22
). Thus, if someone is exposed to fluorescent lights on a daily basis, the damage may build and eventually result in clinically apparent changes. Several studies have substantiated this principle by demonstrating that even suberythemal doses of UVR can elicit erythema if applied to the skin chronically (21
). Moreover, repeated exposure to suberythemal doses of UVR within short enough time frames sensitizes the skin, causing the minimal erythema dose to decrease in a time-dependent manner (21
Collectively, these studies indicate that the risk of chronic exacerbation of photosensitivity from frequent exposure to CFLs is not negligible. Moreover, the action spectra used indicate significant variability in terms of the bulbs’ erythemal, NMSC and general S(λ) UV hazard. Until further studies are performed to determine what dose of UVR is safe in photosensitive patients, it would be prudent for these individuals to protect themselves by using bulbs with the lowest UV emission and effective irradiance. Unfortunately, given the variability of UV hazard from covered CFLs, and the lack of distinguishing package labeling (, lower) it is challenging for photosensitive patients to know which bulbs are safest. We would therefore encourage physicians to refer to , and when making recommendations to patients.
We urge responsible lamp manufacturers to provide alternative UV-safe bulbs that are clearly marked with an internationally recognizable symbol, as proposed in , consisting of the letters “UV” set inside a circle bisected by a diagonal slash. Aside from providing much needed information to photosensitive patients, the use of such a symbol, coincident with the development of relevant consensus standards, has other applications to general lighting. These broader applications include protection of artwork in homes or museums, prevention of color fading of products and packaging in retail environments and in UV-sensitive manufacturing processes.
Proposed symbol to mark UV shielded compact fluorescent lamps. The internationally recognized format of this symbol will permit the unambiguous selection of lamps that are encapsulated with effective UV blocking materials.
Until lamp manufacturers provide improved UV hazard label information, individuals that are particularly vulnerable may prefer to use appropriate personal UV meters, as recommended by the XP society, to actually implement this precaution.