Filter radiometry based on direct utilization of trap detectors

A new design for a filter radiometer based on a trap detector, a set of temperature-controlled filters, and a precision aperture is described. This filter radiometer can be used to realize high-accuracy scales for illuminance, luminous intensity, and spectral irradiance. The new filter radiometer is an improved version of our earlier designs. It has been improved in such a way that the filter can be easily and reliably changed. This makes it more suitable for spectral irradiance measurements, where lamps usually have to be measured at several wavelengths. The results of the characterization of the filter radiometer equipped with a lambda filter using two different methods are presented. The results are in agreement at the level of 0.3%.