A new apparatus with high radiation energy between 320-460 nm: physical description and dermatological applications

A new apparatus (UVASUN 5000) is presented with high radiation energy between 320-460 nm. The measurable energy below 320 nm was shown to be many orders of magnitude too low to produce erythema. The radiator is a specially developed source for high UV-A intensity, housing a quartz bulb with a mixture of argon, mercury and metal-halides. At a skin-target distance of 0.2 m the size of the irradiated area is 0.35 X 0.35 m, and the measured mean UV-A intensity is about 1400 W . m-2 (140 mW . cm-2). The UV-A energy in the range of 320-400 nm is about 84% of the total radiation energy. Effects of very high doses of UV-A on human skin were studied. Following single UV-A applications the minimal tanning dose UV-A (MTD) and the immediate pigment darkening (IPD) dose of UV-A were established. The calculated IPD threshold time was 1.8 min at 0.2 m. Repeated exposure to this UV-A delivering system yields long lasting dark brown skin pigmentation without any clinical or histological signs of "sunburn" (UV-B) damage, epidermal hyperplasia or thickening of the stratum corneum. The instrument was also successfully used for photo-patch testing and reproduction of skin lesions of polymorphous light eruption. Minimal therapeutic results were seen in the phototherapy of vitiligo and inflammatory acne.