Visual performance or visual
efficiency is the ratio of performance under less than ideal illumination to that
under ideal illumination. Performance may be time taken to carry out a given task,
The effect of illuminance on visual
performance is shown in Figure 3, which has the following points:
(i) Increasing the illuminance on the task
produces an increase in performance following a law of diminishing returns.
(ii) The illuminance at which performance
levels off is dependent on the visual difficulty of the task, i.e. the more
difficult the task, the higher the illuminance at which performance saturates.
(iii) Although increasing illuminance
increases task performance, it is not possible to bring a difficult visual task to the
same level of performance as an easy task simply by increasing the illuminance.