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Exposures to UV radiation from solaria and sunlight have potentially damaging and beneficial effects that are not yet fully quantified. Here we compare weighted UV irradiances relevant to erythema (sunburn) and vitamin-D production from 2 phototherapy units and 2 commercial solaria with those under clear-skies in summer and winter at Lauder New Zealand (45°S). We find that weighted irradiances from one solarium are an order-of-magnitude greater than for summer sunlight whereas the others are comparable with summer sunlight, and an order-of-magnitude greater than winter sunlight. For most solaria, UV-A irradiances far exceed those in sunlight, constituting a potentially serious health risk. The calculated vitamin D benefit to erythema risk ratios for the solaria are comparable to, or greater than for with summer sunlight, and significantly greater for one of the phototherapy booths (the predominantly UV-B booth). Exposure times to maintain sufficient vitamin-D without inducing erythema are extremely short for the latter solarium, whereas for the others they are comparable to, or less than, those for summer sunlight. For winter sunlight, deduced exposure times for vitamin-D sufficiency are impractically long. In conclusion, the solaria tested should be capable of helping to maintain vitamin-D sufficiency. However there is an attendant risk of erythema; and exposure times are sensitive to the choice of action spectrum. For all solaria the spectrum differs greatly from sunlight with unnaturally high irradiances at some wavelengths, which could have adverse health effects. Their use is not advocated as a way of ensuring vitamin-D sufficiency.

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