Calibration procedure for UV-365 integrated irradiance measurements
George P. Eppeldauer, Thomas C. Larason, Robert E. Vest, Uwe Arp, Howard W. Yoon
Since the CIE standardized rectangular-shape spectral response function for the 320 nm to 400 nm wavelength range can be realized only with large spectral mismatch, the realized UV-A meters have different response functions resulting in large errors in broadband UV measurements. Instead of using the rectangular-shape CIE functions, a reference UV 365-nm LED source and a calibration procedure are standardized here for uniform broadband UV measurement. The requirement from the calibration procedure is to obtain invariance in the measured output signal for variations in both the peak and the spectral width of the source and the spectral-shape of the meter response. From the signal, measured using the spectrally calibrated source and meter, both the integrated irradiance (from the UV-365 reference irradiance source) and the integrated responsivity of the reference irradiance meter can be determined. Test UV meters can be substituted for the reference UV meter. From the obtained calibration factor and the integrated response of the reference meter, the integrated response of the test meter can be determined. When the calibrated test meter measures the signal from a field UV source, the integrated irradiance from the field source can be determined. The measurement uncertainty obtained using the reference UV source and the broadband UV calibration procedure, was 5 % (k=2).