Visibility of targets: Model for calculation

The introduction of the visibility level as a criterion for the obtainable visual information necessitates a metric to allow its quantification. On the basis of Adrian's, Aulhorn's and Blackwell's data a method has been developed to compute the luminance difference thresholds ΔL of visual targets of variable size and positive and negative contrast. Another parameter relevant to ΔL is the observation time to cope with practical viewing conditions in which fixation was found to be restricted to 0.1 to 0.2 s. The effect of age on the threshold contrast and that of disability glare has been incorporated. The numerical description allows the determination of the visibility level VL of objects in the visual field. A practical example of how to obtain VL is presented.