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Abstract
It is known that temporal modulation of the source illuminating a scene can affect visual performance. Nevertheless, there is a lack of evidence showing this in a natural setting with a simple, natural task. We devised a simple test of visual function using a pencil and paper visual search technique − identifying low-contrast printed numbers on the sheet of paper. We measured the effect of the temporal modulation of the fluorescent lighting upon visual performance on this task. We constructed two office environments lit with both tubular and compact fluorescent lamps, completely identical except for the lamp ballasting. Office A equipped with electronic ballasts, producing a light emission mainly modulated at 60 kHz having a modulation percentage of 3 percent for 100 Hz component; office B equipped with magnetic ballasts, producing a temporally modulated light which fundamental component—100 Hz frequency—has a modulation percentage of 32 percent).
Fifty students aged 20 to 22 years performed the same simple visual search tasks (errors were not allowed) under two lighting conditions. This permits evaluation of visual performance by analysis of a single dependent variable, the time taken to complete the task. An analysis of variance (considering only the complete data of 39 subjects) shows that the “modulation” factor is statistically significant (F(1,37) = 10.21, p < 0.00285). At the end of the session, the observers performed a subjective appraisal of the lighting, by means of a simple questionnaire for each lighting condition. A within-subject ANOVA shows that mean values for each factor in both offices are indistinguishable within a statistical significance level of 5 percent. These results confirm the hypothesis that the observers, even though they cannot visually discriminate between the two light modulation conditions, show significantly higher visual performance when performing the task in low modulation condition. Additionally it was suggested that the method would be capable of identifying the more sensitive individuals in the group.