New sector-disk method for comparing light intensities.

A method of using two rotating sector disks to attenuate a beam of light by an exact integral factor is described. The method provides a means for measuring intensity ratios or filter transmissions without errors due to detector nonlinearity, provided that the detector obeys Talbot's law, and has a number of advantages over the ordinary sector-disk method used for this purpose. An apparatus for testing whether the detector obeys Talbot's law is also described.