Visual Performance
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Visual Performance/Visual Efficiency

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, productivity, etc.

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.

Figure 3 Improvement in Visual Efficiency for Various Tasks