STUDY ON THE RELATIONSHIP BETWEEN ILLUMINANCE AND CONTRAST OF TARGET AND BACKGROUND FOR VISUALLY CHALLENGED PEOPLE

Abstract

 In this study, the authors have sought under laboratory conditions to evaluate visually challenged subjects and their preferred level of brightness using three categories: those which are i) barely visible ii) easily visible iii) too bright to be visible.
 On the visual targets, four types of achromatic-color lines at 7.5 cm in width were placed one by one on A4-size backgrounds of different achromatic colors; these were designate N9 and N3. The lines were combined with the backgrounds in a total of seven ways to create a combination of luminance contrasts. These visual targets were displayed on a vertical wall facing the experimental apparatus at a visual distance of 1m.
 The subjects evaluated each illuminance value with three types of criteria: barely visible, easily visible and too bright to be visible. As a result of this research, the authors determined that the relationship between illuminance and contrast for visually challenged people, is as follows;
 (1) The result of illuminance was not affected of visual acuity and impact of eye disease of visually challenged subjects.
 (2) The illuminance of visually challenged subjects varied in individuals and was larger than the young. Also, the data of "barely visible" evaluation in increasing in brightness was higher than decreasing.
 (3) A percentage of 28 to 35 of visually challenged subjects evaluated "too bright to be visible" under 1000lx.
 (4) The ratio illuminance of "easily visible" in the background N9 was 29 to 120 times higher than "barely visible" in increasing in brightness, and the ratio illuminance of "easily visible" was 12 to 62 times higher than "barely visible" in decreasing in brightness. The ratio of "easily visible" in the background N3 was 46 to 90 times higher than "barely visible" in increasing in brightness, and the ratio illuminance of "easily visible" than "barely visible" was 24 to 42 times in decreasing in brightness. Therefore, these numbers of ratio in decreasing in brightness were about a half of the increasing conditions.
 (5) The illuminance of "easy visible" of visually challenged subjects was 0.6 to 1.7 times higher than that of the young subjects, and the illuminance of "barely visible" of visually challenged subjects was 15 to 82 times higher than that of the young subjects.
 (6) The authors showed the percentile values of the illuminances of visually challenged subjects.
 (7) Using the percentile values of illuminance, the authors showed the figures and the regression equation by the relationship between the illuminance and luminance contrast of "proper illuminance range" and "optimum illuminance range".
 (8) The comparison of the illuminances in positive and reverse contrasts, it was reversed at the specific conditions.