Full Title

Photometry, e.g. photographic exposure meter (spectrophotometry G01J3/00; specially adapted for radiation pyrometry G01J5/00 ) > by comparison with reference light or electric value > intensity of the measured or reference value being varied to equalise their effects at the detectors, e.g. by varying incidence angle > using a variable element in the light-path, e.g. filter, polarising means (G01J1/34 takes precedence) > using electric radiation detectors