Comparison of Brightness Judgment of Space between Observer within and Observer Looking into Space

To compare brightness judgment, we conducted two experiments. In the first one, the observer evaluated the brightness of a space while within it (“observer's space”) by determining the illuminance of another room which gives an impression of equal brightness to that of the “observer's space”. In the second one, the observer evaluated the brightness of a space while looking into it through a small window (“observing space”). We also examined the influence of the lightness of the interior wall of the space and the existence of white paper upon brightness judgment in both situations. Results showed that the brightness of the “observer's space” was judged higher than that of the “observing space”. White walls were evaluated as brighter than black walls in both the “observer's space” and the “observing space” while illuminance of the space was kept constant. A space was judged brighter with a piece of white paper than without it especially in the “observing space”, which indicates the effect of white paper is eminent in the condition.