Characterization and calibration of broadband ultraviolet radiometers

Abstract

The band responsivities of radiometers for measuring ultraviolet irradiance or dosage in the UVA, UVB and UVC spectral regions are source-dependent and require spectrally weighted measurements for calibration. Currently, however, many industrial users lack knowledge of this and may use a radiometer originally calibrated using one particular type of source to measure UV radiation from a source of a different type. Worse still, when this radiometer is later sent for recalibration, the calibration laboratory could use a source of a third type. This problem results in considerable discrepancies, as high as 20 % to 50 %, in the calibration of UV radiometers, and consequent errors in actual measurements. Efforts are being made by the International Commission on Illumination (CIE) to standardize the calibration method and industrial uses of UV radiometers. This paper reviews the measurement principles of broadband radiometers and examines, both theoretically and experimentally, the effects of spectral distribution on the responsivities of several commonly used UV sources. The analysis agrees well with the experimental results. The methods of characterization and calibration of these radiometers are also discussed in detail.