A circular transparency which duplicates the decay characteristic of a P-7 phosphor is carried by a rotating annulus. The density gradient of the transparency is such that the luminance of a given point on an illuminated screen in front of which it is rotated decreases with respect to time in the same manner as the luminance of a phosphor after excitation. The annulus is rotated at different speeds by a synchronous motor through a system of change gears and a friction drive. The spectral characteristic of the phosphor is duplicated as closely as possible by the use of an appropriate Wratten color filter. Variations in over-all brightness of the presentation are obtained with polaroids and neutral density filters. A wide range of contrasts between the "target" and background is achieved by using a small piece of Cellophane cut in the desired shape to represent the target. This is located between the polarizer and the analyzer. Variations of luminance of the target and background are obtainable independently by appropriate changes in the relative orientations of the optical axis of the Cellophane and the axes of polarization of polarizer and analyzer.

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