AbstractA heterochromatic brightness or lightness match, established at photopic levels, is not expected to hold at lower adapting luminances. This applies, in particular, to the Purkinje Effect, concerning the red‐blue comparison. The fact that a “blue” stimulus mainly involves the shorter wavelengths favors the interpretation in terms of rod intrusion, coming gradually into play as the eye, pre‐adapted to a photopic level, is becoming adapted to a mesopic or scotopic one. The two experiments described in this paper aim to put into evidence some effects that are likely to be due to postreceptoral mechanisms, and which may confuse the student faced with a practical demonstration of the Purkinje Effect. In particular, we consider the blue lightness enhancement after an abrupt decrease in adapting luminance, and the decay of lightness‐luminance discrepancy of narrow‐band stimuli during the reco