GB914820A - Improvements in apparatus for colorimetry - Google Patents

Abstract

914,820. Photo-electric colorimetry. EGYESULT IZZOLAMPA ES VILLAMOSSAGI R.T. March 25, 1959 [March 26, 1958], No. 10381/59. Class 40 (3). In an arrangement for measuring the chromaticity of a light source, e.g. a fluorescent lamp 21 (Fig. 9), light from the latter which passes through a slit 22 is collimated by lens 23 and then passes through an interchangeable template 24 and a (metal) interference filter 25 and is then imaged on a photo-electric device 27 by means of lens 26. The interference filter (Fig. 1) which produces monochromatic has a spectral transmission ## as shown in Fig. 2. In the present invention the chromaticity co-ordinates are computed from the response of the photo-electric device which, in the case of the #X# co-ordinate is equal to #S##X#d# where S# is the spectral distribution of the light source. The co-ordinate X#, which over the range considered, varies as shown in Fig. 4, and which may be computed from the tristimulus co-ordinate X = #<SP>780</SP> 880 S##X#d# is utilized in conjunction with the spectral response of the photo-electric device ## (Fig. 3) to produce an apertured template as shown in Fig. 5, or, preferably as in Fig. 6, representative of a function different templates being produced for the co-ordinates #y# and #z#. These templates are then successively positioned at 24 (Fig. 9) and the chromaticity computed from the response of the photo-electric device by using the relationship given above. If desired, three separate interference filters and a template having three apertures corresponding to the different coordinates may be selectively exposed in the same optical path between the lenses 23, 26 (Fig. 10, not shown). By arranging the template 24 (Fig. 9) to produce a sensitivity corresponding to the function #y# and employing a diaphragm (Fig. 11, not shown) having eight adjustments, each corresponding to the transmission of light in beam wavelength bands, the arrangement of the invention may be employed to measure colour rendition.