THE EFFECT OF LIGHT SOURCE COLOR AND INTERIOR COLOR ON THE PERCEPTION OF DIMMING LIGHT IN OFFICE

 Light control systems using motion sensor save energy consumption in office efficiently. It is also known that rapid change of illuminance might cause unpleasantness to workers. To solve this problem several researches studied the relation between workers' perception and the way of dimming of luminaires around workers, however they did not focus the effect of the light source color. Although there are many discussion and doubt, Kruithof curve is a famous theory, that there are pleasant or unpleasant combination of illuminance and color temperature. Here our question arises that workers' perception on the change of illuminance might be influenced by the impression of the combination of illuminance and color temperature before and/or after the fluctuation.<br> Thus, we conducted three experiments in an experimental room, focusing two points. The first was perception of different color temperature in a room with achromatic, that is white wall, and the second was with different color temperature and chromatic wall color. The size of the room is W3.5m x D3.5m x H2.7m. In the achromatic phase, three color temperature, 3000K, 5000K and 6500K were presented by LED luminaires on the ceiling. In the chromatic phase the same three (or two of 3000K and 6500K) color temperature were combined with four wall color, orange, pale orange, blue and pale blue, covering existing white walls with color cloth of 1.5 m height from the floor. In one session of the experiment color temperature and wall color were fixed to one and illuminance was fluctuated several times with different ending level and speed randomly. Starting illuminance was fixed to 750 in this research, and ending illuminance and speed were decided according to the existing research. 20 students participated at every experiments. During the session, participants were doing a task to search about one question with a laptop PC and write down the findings on a paper, and also instructed to fill the questionnaire every time they perceived the change. Dimmed illuminance recovered to the starting level with longer seconds. At the end of the experiment, participants evaluated the pleasantness of the room with each of the all combination of wall color, color temperature and illuminance at the stating/ending time of the change.<br> The results show that with white wall the perception ratio is statistically lower at 5000K than at 6500K. There is some tendancy that the perception ratio is relatively higher when the color of lamp and wall is similar ones, that is, blue wall and 6500 K or orange wall and 3000 K, though this tendency was not found when the color of wall was pale, whitish one.<br> Finally, participants' evaluation of pleasantness on each combination of wall color, color temperature and illuminance before and after the change were compared to the perception ratio of the experiments. It was found that negative subjective impression of the combination before/after the change leads to higher perception and positive impression show the opposite results.