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Abstract: In this experiment four types of lighting sources with differentcolour rendering properties are used in turn to illuminate two kindsof visual task separately. The visual acuity under each condition has been measured andcalculated. It is found that raising the colour rendering index of thelighting source could increase the visual discrimination effect in reco-gnizing the black signs against coloured background; while decreasingit in recognizing the coloured signs against grey background. These eff-ects are mainly the results of the function of luminance contrast betweenthe details and the corresponding backgrounds under different lightingsources. The results agree with the relationship of V=f(c) which isbased on the visual performance of human observers. Besides, it showsthat the coloured details against grey background are better definedthan the black detail against coloured background in visual discrimin-ation, and the colour contrast plays an important role in advancingvisual acuity. It is proved that the high pressure sodium lamp (HPSL)is one of the best lighting sources for the former sign pattern in raisingvisual acuity and saving electric energy in spite of. its lower colourrendering property.

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