Figure 5. Graph shows the contrast threshold of the human visual system at close inspection (30-cm) and normal viewing (60-cm) distances. The curves correspond to the logarithmic averages, <L>, of four typical luminance ranges shown in Figure 4. The curves are based on the theoretical fits of Barten (9) to the data of van Meeteren and Vos (10) with the angular size of the object limited to 1°, the solid angle subtended by the fovea.