Reusable ultraviolet monitors: design, characteristics, and efficacy.

Reusable ultraviolet dosimetry badges have been developed that provide a visual indication of daily cumulative ultraviolet (UV) exposure. These two-sided, tapelike devices measure UV radiation emitted by sunlight or an artificial UV light source exposure by means of a photochromic aziridine color change reaction that is UV-integrating but optically reversible. UV radiation falling on the exposure side of the badge generates a color change that can be seen from the opposite or readout side. End points are indicated by a visual match of the photochromic with a surrounding reference. This paper describes the construction, component characteristics, and clinical testing of two versions of a new photochromic dosimeter that selectively responds to either UVB (280-320 nm) radiation or UVA (320-400 nm) radiation of the solar spectrum. One version of this monitor, sensitive only to the mid-range UVB, has a peak sensitivity to 300 nm and has four end point markers revealing color changes corresponding to 0.4, 0.8, 2.2, and 6.5 times the minimal erythema dose of an average Caucasian. A second version, sensitive only to UVA, has a peak sensitivity at 355 nm and can monitor exposures ranging from 0.8 to 10 joules/cm2. Outdoor efficacy testing has shown that the UVB monitor is an effective predictor of UV dose-related 24-hour erythema response induced by sunlight. Following a measurement, these monitors can be rezeroed by exposing the readout side to sunlight for a few minutes. They can be reused for eight to ten times. The limitation of the sunlight-calibrated UVB monitor tag is its failure to predict erythema response produced by artificial UVB sources such as FS40 sunlamps.