The brightness enhancement of flickering light was measured as a function of illuminance, wavelength and target size. Data obtained with stimuli of seven different wavelengths show that the spectral composition has virtually no effect upon this Brücke-Bartley effect. When the illuminance was decreased the frequency at which the enhancement was found to be maximal, decreased too. In addition to the brightness gain the apparent hue shift was determined too. This shift might be explained by the Bezold-Brücke phenomenon and a possible phase shift between the different colour signals. Von Békésy's model of a neural unit accounts for some of the details when the target size is decreased below 30 min of arc. © 1969.