The subjective appraisal of the permissible luminance of the light source reflecting on the papers

Reduction of reflected glare on such visual tasks as works on printed papers in an office is one of the most important factors of office lighting designs.Conventional evaluating method based on the contrast of printed characters to thebackground paper is complicated for practical lighting design works.Experimental studies have been carried out to find out a practical design guide of permissible luminance limits of reflected light source related to the illuminance on a paper.As objects for visual tasks, printed papers in six reflectance combinations of characters and papers by white, gray and black were adopted.Authors adopted the total feeling levels of the permissible reflection including the legibility of the characters as the criteria.The results are:(1) As far as the experimental condition using 40W fluorescent lamp lightng fittings, reflection of light source is permissible for a wood free paper and a mechanical printing paper.(2) In the most general case of black characters on a white art paper, the practical guide of the permissible luminance for 500 lx illuminance design would be 1800cd/m2 for uniform luminance light source, 4500cd/m2 for non-uniform luminance light source, in terms of category “Agreeable”.