Pupillary light reflex, receptive field mechanism and correction for retinal position for the assessment of visual discomfort

Light sources causing annoyance or pain produce discomfort glare. Traditional glare metrics fail for non-uniform luminaires. As an alternative, visual discomfort is determined by a model incorporating the centre–surround receptive field mechanism, the pupillary light reflex and a correction for retinal position. The pupil area, controlled by the pupillary light reflex, regulates the retinal illuminance. A centre–surround receptive field, described by a difference of Gaussians, represents the visual signal. A correction according to the Guth position index accounts for the reduction in brightness perception when a light source is moved away from the line of sight. The model is analysed with a forced choice paired comparison experiment involving 17 non-uniform rear projected stimuli with different spatial frequencies and luminance steps. A coefficient of determination of 0.68 between the subjective assessment and the model is obtained. A paired comparison office luminaire experiment and a magnitude estimation experiment involving diffusor luminaires validate the model resulting in a coefficient of determination of 0.86 and 0.81, respectively. By including the pupillary light reflex, receptive field mechanism and a correction for retinal position, the more physiologically justified model is a promising alternative to current, often empirical, glare metrics, especially for non-uniform luminaires.