Description
Class G01J : MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRA-RED, VISIBLE OR ULTRA-VIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
Subclass 1/28: Photometry, e.g. photographic exposure meter (spectrophotometry G01J 3/00; specially adapted for radiation pyrometry G01J 5/00) by comparison with reference light or electric value intensity of the measured or reference value being varied to equalise their effects at the detector, e.g. by varying incidence angle using variation of intensity or distance of source (G01J 1/34 takes precedence)