Optical equipment was developed to simulate visual display terminals (VDTs) with reversed presentation (bright background and dark characters). The decay time and mean luminance were kept constant, while the oscillating frequency varied. During one experiment subjects had to read text aloud for 60min. Before and after the reading, near point distance, critical flicker fusion frequency (CFF), visual acuity, stereo depth perception, lateral heterophoria and contrast sensitivity were measured. The 30 subjects had then to report their subjective reactions on a questionnaire. The following frequencies were used: 0, 30, 60, 90, 180 Hz. In addition subjects read a normally printed text with a luminance of 75 or 150 cd/m2. The main finding was that of a strong decrease of the CFF after exposure to 30 and 60 Hz. It is suggested that for reversed presentation the refresh rate should be higher than 90 Hz.
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