3. Visibility of visual tasks with and without intrinsic luminances

The definition of recommendations and then standards concerning the ability to perform a visual task has been a constant preoccupation of organizations concerned with lighting. Although these recommendations have been refined over time, for practical reasons they have always been given in terms of illuminance. We may wonder why this distortion of the reality of the visual system, which is sensitive to luminance rather than illuminance, has led to satisfactory results in the majority of cases. This is because, until the 1970s, the majority of visual tasks had no intrinsic luminance. On the contrary, with the widespread use of visualization consoles, the industrial world was invaded by visual tasks with intrinsic luminance, which led in the 1980s to a large number of faulty implementations.

It's easy to illustrate the behavior of a visual task without intrinsic luminance...