From the viewpoint of conservation, ICOM recommends illuminants of 50 lx（2900 K）or 150-180 lx（4000 K） for museum lighting. However, they are rather dark, compared to everyday lighting about 200-1000 lx. Moreover, previous studies that examined the impression of artworks with regard to lightening reported that paintings were rated as more beautiful under bright illumination. To confirm this finding, we extensively investigated the effect of lightening on the impression of paintings in three experiments. In Experiment 1, observers rated paintings as more beautiful under a bright condition（1350 lx） than darker ones（50 or 150 lx）.In Experiment 2, little or no effect of color temperature was found. In Experiment 3, in which observers had enough time to adapt to lightening, no effect of lightening was found. This result disagreed with Experiment 1 or the previous studies. It is therefore suggested that observers rate paintings as more beautiful under bright illumination when they insufficiently adapt to the illumination. In addition, we confirmed horror and weirdness of artworks were felt strongly under lower illuminance or higher color temperature.