The main visual functions and their dependence on lighting 1
The main visual functions are: visual acuity, contrast sensitivity, speed of discrimination, as well as the stability of clear vision, color discrimination, light and dark adaptation, accommodation, critical frequency of flicker, etc.
Visual acuity is the maximum ability of the eye to distinguish the smallest details of an object (points, dashes, circles) as separate from each other. It is determined by the smallest angle at which two adjacent points are visible as separate. It is conventionally believed that visual acuity is equal to unity if the resolution angle is 1 minute, which corresponds to the conditions for examining a 1.45 mm-sized part at a distance of 5 meters. With an increase in illumination to 100–150 lux, it increases rapidly, with a further increase this growth slows down.
Contrast sensitivity – the ability of the eye to distinguish the minimum difference in brightness between the object (part) and the background or two adjacent surfaces. The dependence of contrast sensitivity on the lighting conditions of the object in question and the brightness to which the eye has adapted perfectly has been established. Optimum working surfaces of the luminance of several hundred cd / m 2 (≈500), and of the investigated objects is much higher. It is extremely important to correlate the brightness of the object and the background in the work of the surgeon. If the working surface reflects no more than 30–40% of the incident light, then the contrast sensitivity is highest when the illumination is 1000–2500 lux.
The speed of discrimination or the speed of visual perception is the smallest time required to distinguish between parts of an object. It increases markedly with an increase in illumination to 100–150 lux, then its growth slows down (but does not end) to 1000 lux and higher.
All three of these functions are closely interrelated and determine the integral function of the visual analyzer. They are also used in hygienic regulation of lighting.