A new UKAS accredited calibration system for ultraviolet radiometers

A system has been designed to provide traceable calibration of ultraviolet (UV) radiometers used with broadband and extended sources of the type commonly employed in clinical phototherapy and photobiology research. Traceability requires both an unbroken chain of steps to the primary standard held by a national laboratory and the checking of those steps by an accreditation body. The system described is traceable to the cryogenic radiometer at the National Physical laboratory (NPL) and is accredited by the United Kingdom Accreditation Service (UKAS). The best expanded uncertainty that can be obtained for single wavelength irradiance responsivities is 7% (at 95% confidence) in the wavelength range 250-400 nm. The measured meter characteristics are used along with tabulated data on the spectral properties of the source and, if required, the action spectrum of the radiation to calculate an appropriate calibration for the meter.