Luminance and stimulus purify of VDT display color in terms of readability

A study was undertaken to investigate the relations among luminance, stimulus purity, and Visual Display Terminal (VDT) display color readability, and to clarify the relation between readability and color impression. Four levels of stimulus purity for orange, five levels for green, and five for purple blue, and white and black were examined by a paired comparison method and a questionnaire regarding impression observed for the colors under two levels of illuminance and three levels of luminance. Questionnaire replies indicated that each color had an optimal stimulus purity, in terms of readability, which was from 0.2 to 0.5, independently from illuminance and luminance. Men's readability scores for higher stimulus purities than the optimal value, did not notably decrease, while women's scores were severely lower than the optimal value. In case of short dominant wavelength, readability was higher under low luminance than under other luminances. By applying the Semantic Differential method to answers to the questionnaire, “Conspicuous factor” and “Uncomfortable factor” were extracted, which were closely related to color readability.