Personal solar UV Exposure Measurements Employing Modified Polysulphone with an Extended Dynamic Range†¶

Ultraviolet radiation thin film dosimetry: A review of properties and applications

Spectroradiometry, radiometry, and dosimetry are employed for the measurement of ultraviolet radiation (UVR) irradiance and non-ionizing exposure. Different types of UVR dosimeter have been developed for measuring personal and environmental UVR exposures since film dosimetry was pioneered in the 1970s. An important type of dosimeter is the thin film variant, which contains materials that undergo changes in optical absorbance when exposed to UVR. These changes can be measured at a specific wavelength using a spectrophotometer. Thin film dosimeters allow UVR exposure measurements on humans at various body sites during daily activities, as well as on plants, animals, and any sites of interest when utilized in a field environment. This review examines the properties and applications of five types of thin film UVR dosimeter that have different dynamic exposure limits and spectral responses. Polysulphone, with a spectral response approximating the human erythema action spectrum, was one of the first materials employed in thin film form for the measurement of UVR exposures up to 1 day, and up to 6 days with an extended dynamic range filter. Polyphenylene oxide has been characterized and employed for personal UVR exposure measurements up to approximately four summer days and has also been used for long-term underwater UVR exposures. Phenothiazine and 8-methoxypsoralen have been reported as suitable for the measurement of longer wavelength UVA exposures. Finally, polyvinyl chloride with an extended dynamic exposure range of over 3 weeks has been shown to have predominantly a spectral response in the UVB and extending up to 340 nm.

Optical Attenuators Extend Dynamic Range but Alter Angular Response of Planar Ultraviolet-C Dosimeters

Effective ultraviolet-C (UV-C) decontamination protocols of N95 respirators require validation that the entire N95 surface receives sufficient dose. Photochromic indicators (PCIs) can accurately measure UV-C dose on nonplanar surfaces, but often saturate below doses required to decontaminate porous, multilayered textiles like N95s. Here, we investigate the use of optical attenuators to extend PCI dynamic range while maintaining a near-ideal angular response-critical for accurate measurements of uncollimated UV-C. We show analytically that tuning attenuator refractive index, attenuation coefficient, and thickness can extend dynamic range, but compromises angular response unless the attenuator is an ideal diffuser. To investigate this tradeoff empirically, we stack PCIs behind model specular (floated borosilicate) and diffuse (polytetrafluoroethylene) attenuators, characterize the angular response, and evaluate on-N95 UV-C measurement accuracy within a decontamination system. Both attenuators increase PCI dynamic range >4×, but simultaneously introduce angle-dependent transmittance, which causes location-dependent underestimation of UV-C dose. PCI-borosilicate and PCI-polytetrafluoroethylene stacks underreport true on-N95 dose by (1) 14.7% and 3.6%, respectively, when near-normal to the source lamp array, and (2) 40.8% and 19.8%, respectively, in a steeply sloped location. Overall, we demonstrate that while planar attenuators can increase PCI dynamic range, verifying near-ideal angular response is critical for accurate UV-C measurements.