Detector for measuring optical properties of CRT faceplate - uses halogen light source, optical fibres and photodiodes to detect reflected components in selected frequency bands for grey scale evaluation

摘要

The apparatus (10) for determining the characteristic grey scale factor of bright and dark video screens e.g. TV screens (11) has a light sensor assembly (28) which responds principally to the light reflected from the inner surface of the screen. A halogen light source (17) projects light via a optical fibre (19) and the resultant reflections are transmitted via a bifurcated optical fibre (20) to an evaluation unit (16). After filtering (21,22) the light intensities within a range 450/650 nm and a range 700/800 nm are detected by the photodiodes (18) and compared for derivation of the required factor (36). USE/ADVANTAGE - For measurement before or after completion of tube. Enables precise determination of light characteristic for all types of screen and is of simple construction readily installed on continuous production line. Is largely independent of distance variations between screen and incident beam. Comparison technique minimises errors due to stray light or drift in evaluation circuitry.