Effect of intermittent light on the readability of printed matter under conditions of decreasing contrast.

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Abstract
The effect of intermittent light on the recognition of printed matter was studied by applying the effect of enhanced brightness (Bartley effect) for the improvment of visibility under conditions of low brightness contrast. A reading chart with gradually decreasing contrast was read under steady and flicker illumination with 4 different light-dark ratios (aperture size of the episcotister: 90[degree], 180[degree], 270[degree], and 345[degree]) and 2 flicker frequencies (9 and 15 c.p.s.). The luminous reflectance of the chart varied from 33.2 ft.-L (Line 1) to 5.6 ft.-L (Line 50). The number of lines read under each condition served as index of readability and, in a broader sense, as index of visibility under low brightness contrast. It was found that the effect of flicker light was to lower the number of lines read, especially at low levels of illumination.
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