Abstract: Four experiments are reporfed in which natural daylight and threeartificial sources were compared as to their visual effects under equalilluminance in a diffuse lighting environment. The criteria used were discrimi-nations of size, contrast, probability for accuracy of detection and visual fatiguemeasurements. The results indicated that natural daylight shoed better visualeffects than artificial light sources, while there is no significant difference forincandescent, fluorescent and high pressure mercury lamps. It is concluded thatin prescribing illumination standards a unified value should be specified fordifferent light sources.

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