A color saturation threshold meter has been designed in which a gradually changeable mixture of white and colored light is produced. The variability of the mixture is produced by means of double refraction. A ray of white light is split into two beams; one traversing a color filter. The two rays are then reunited so that a homogeneous mixture of white and colored light is obtained. Polarization of the two rays involved permits a measurable change in the ratio of luminances of both lights between limits of zero and infinity. The instrument works satisfactorily in its present state. Yet, it could be rendered more useful by the following two devices which can easily be installed: (1) Instead of colored filters, interference filters producing an approach to spectrally homogeneous light can be installed. (2) Application of neutral density filters of proper dimensions would provide constancy of the mixture’s luminance throughout the measuring range; a condition which is only approximated for a limited range in the present instrument.
HEINZ HABER and HORST FLECK, "A Color Saturation Threshold Meter," J. Opt. Soc. Am. 40, 459-461 (1950)