This paper describes the merit of daylighting by comparing the physical and psychological aspects of light and heat radiation. We prepared three rooms: direct lighting with fluorescent lamps; indirect lighting with incandescent lamps; and daylighting alone. We conducted physical measure-ment associated with light and heat, together with subjective experiments in terms of luminous and thermal sensations.The measurement was done in August, 2006, and also in December, 2007. In summer, the air temperature of the room with daylighting alone was lower than two other rooms with electric lighting. On the other hand, in winter, the air temperature of the room with daylight-ing alone was higher than two other rooms. There was no vote indicating either too bright or too dark in the case of daylighting. Most subjects did not feel heat radiation from lighting except daylight in winter. More than 50% of the subjects prefer daylighting to electric lighting.This confirms that daylighting should be retreated as one of the passive strategies because it creates the moderate brightness while at the same time contributes to creating moderate coolness in summer and moderate warmth in winter.
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