Suprathreshold Area Brightness Relationships

Size-brightness relationships have been studied at four intensity levels (0.1, 1.0, 10.0, and 100.0 ml) for five different stimulus sizes (9, 18, 36, 72, and 144 min of visual angle). The test situation was such as to approximate an applied situation where there is little control over physical conditions. At the lower levels apparent brightness was found to increase with increasing area, i.e., the luminance of the larger stimulus was less than that of the smaller when the two were judged to be of equal brightness. At the higher levels, on the other hand, apparent brightness decreased with increasing area for six out of eight observers. These two deviants showed a tendency in the same direction and might have exhibited the same effect if greater intensities had been used.