New traceability chain for spectral irradiance measurement at LNE-Cnam

Abstract

LNE-Cnam has changed its traceability chain for measuring the spectral irradiance of a light source. This facility allows calibration of spectral irradiance of a standard lamp based on a comparison with a High Temperature BlackBody (HTBB). The reference spectral irradiance is determined by measuring the temperature of the HTBB with a filter radiometer calibrated against our radiant flux reference. This traceability scheme differs from the one used in our former setup, which was mainly based on the International Temperature Scale, ITS-90. Both principles are used in National Measurement Institutes. Our facility uses well known methods [1] adapted to our best capabilities as well as a particular development in optical arrangement and filter radiometer calibration. Thanks to this new measurement setup, our spectral irradiance reference is now traceable to radiometric reference, that is our cryogenic radiometer [2]. We have extended our measurement capability to cover the spectral range from 250 nm to 2500 nm. We have simplified the process by reducing the number of benches (3 in 1) and the number of operations, and we have designed a compact measuring setup through the use of a rotating integrative sphere. This allows us to reduce by at least a factor two our measurement uncertainties over almost the entire spectral range. With this new measurement facility, France participates in the ongoing CCPR k1.a key comparison. This is a key comparison of the Consultative Committee of Photometry and Radiometry for Spectral irradiance from 250 nm to 2500 nm of tungsten halogen lamps. This communication shows the method used, and its validation.