Some principal characteristics of a twin-rotation-disc visibility meter are investigated with respect to the constancy of total luminance at the observer's eye, to the temporal modulation of the task and veiling light path and to the contrast transmission. By means of an additional veiling light source and an additional neutral density filter in the task light path the performance and applicability of the visibility meter can be improved. The accuracy of the theoretical contrast transmission is limited by residual stray light.
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