Optical radiometry covers a wide range of characterizations on optical radiation and serves as the basis of modern optical metrology along with photometry. It directly underpins the realization of candela, one of the seven SI base units. With the increasing high accuracy demands in high temperature scale validation, earth observing equipment calibration, and the solar photovoltaics, semiconductor lighting and laser performance evaluation, the classic blackbody and lamp based standards can no longer provide the desired traceability.
The cryogenic radiometers can achieve the highest accuracy in the measurement of light and detectors. Using a self-developed absolute cryogenic radiometer with an uncertainty lower than 0.05%, NIM is now able to establish a significantly improved traceability to radiometry and photometry, with the wide-range wavelength tunable laser and standard photo-detectors being the intermedia. The uncertainty of the spectral irradiance responsivity from visible to near infrared was dramatically reduced to about 1/5 of that of the traditional traceability. The national measurement capacity in the whole optical metrology area will benefit from these achievements.