Effects of the Uniform Surrounding Luminance On the Luminance Difference Thresholds of Foveal Vision

The physical veiling in the eye arising from stray light falling on the fovea from the surrounding fi eld of view causes a rise in the physiological adapting luminance of the fovea and a rise in the physical luminance of the test stimuli (object and its background). Using a uniform surrounding field with an outer diameter of 33° and with an inner diameter of 3°, the effects, on the luminance difference threshold of foveal vision, of increasing the physiological adapting luminance and of increasing the physical background luminance, caused by physical veiling, have been investigated independently.The results of the experiments show that the rise in the physiological adapting luminance caused by the surrounding field has a decreasing upon the luminance difference threshold as the luminance of the surrounding field increases.The effect of the rise in the physical luminance of the test stimuli determines mainly the luminance difference threshold caused by the surrounding field, provided that the luminance of the surrounding fi eld is above about 100 cd/m2.