Traceable calibration of ultraviolet meters used with broadband, extended sources

Abstract

A calibration system has been developed to provide increased accuracy in the measurement of the irradiance responsivity appropriate for UV meters used with broadband, extended sources of the type employed in phototherapy. The single wavelength responsivity of the test meter is obtained in the wavelength range 250-400 nm by intercomparison with a transfer standard meter in a narrow, monochromatic beam. Traceability to primary standard irradiance scales is provided via the National Measurement System with a best uncertainty of 7% (at 95% confidence). The effective responsivity of the test meter, when used with broadband extended sources, is calculated using the measured spectral and angular response of the meter and tabulated data on the spectral and spatial characteristics of the source radiance. The uncertainty in the effective responsivity, independent of the source variability, is estimated to be 10% (at 95% confidence). The advantages of this calibration system over existing approaches are discussed.

Occupational Exposure to Solar Ultraviolet Radiation of Polish Outdoor Workers: Risk Estimation Method and Criterion

“…A spectral mismatch correction factor (F) minimized the error in measuring erythemal radiant exposure resulting from a spectral mismatch between irradiance distribution of a standard halogen lamp and solar radiation [18,19]: (2) where l = wave length, S sun (l) = spectral power distribution of solar radiation for terrestrial solar spectral irradiance (AM1.5 reference spectrum), S std (l) = spectral power distribution of a standard lamp, S dos (l) = relative spectral responsivity of a dosimeter, S ery (l) = CIE erythemal reference action spectrum. …”

Calibration of broadband ultraviolet detectors by measurement of spectral irradiance responsivity

“…13 However, we were able to do this with considerably lower mesurement uncertainties than those presented earlier. Commercial UVA and UVB detectors were characterized with the setup.…”

“…Even the concept of irradiance responsivity, often given in units ͓A͑W cm −2 ͒ −1 ͔ or ͓V͑W cm −2 ͒ −1 ͔, may be confusing. The measurement may be carried out with either a monochromator-based setup 12,13 or with a tunable laser. If the detector is used in measurements of light sources with different spectral shapes than that of the source that was used in the calibration of the detector, systematic measurement errors of significant magnitude are introduced.…”

Guidelines on the measurement of ultraviolet radiation levels in ultraviolet phototherapy: report issued by the British Association of Dermatologists and British Photodermatology Group 2015

“…A dose measurement accuracy of 10% is generally considered adequate for clinical phototherapy . In treatment cabins, for example, patient positioning and the nonuniformity of irradiation of the skin due to its curvature may be > 15% .…”

“…However, a meter may provide a reproducible reading without the reading being accurate in terms of the absolute dose (in J cm −2 ). Indeed, it is difficult in practice to calibrate a field UV meter with an accuracy much better than 10% . The UV meter calibration uncertainties quoted by those U.K. laboratories operating to the standard ISO 17025 are typically of the order of 10% and are therefore adequate for most clinical UV dosimetry .…”