Traceable calibration of ultraviolet meters used with broadband, extended sources

A calibration system has been developed to provide increased accuracy in th e 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 wavele ngth range 250-400 nm by intercomparison with a transfer standard meter in a narrow, monochromatic beam. Traceability to primary standard irradiance s cales is provided via the National Measurement System with a best uncertain ty of 7% (at 95% confidence). The effective responsivity of the test meter, when used with broadband extended sources, is calculated using the measure d spectral and angular response of the meter and tabulated data on the spec tral and spatial characteristics of the source radiance. The uncertainty in the effective responsivity, independent of the source variability, is esti mated to be 10% (at 95% confidence). The advantages of this calibration sys tem over existing approaches are discussed.