The purpose of this study was to design spectral power distributions of light sources while considering the color appearance and preservation of artwork under low illuminance by using a “color quality index” called Gx(E). One of the spectral distributions obtained from theoretical calculations was reproduced by using a lighting device with six types of monochromatic LEDs. Subjective evaluation experiments were conducted under various light sources, and the prediction accuracy of Gx(E) was verified.
Theoretical and subjective evaluation of the experiment revealed the following results: (1) The spectral power distribution with the maximum Gx(E) at 10 lx was a narrow band distribution with red (630 nm), green (530 nm), and blue (470 nm), and it was called LED-RGB. (2) The subjective evaluation results corresponded well with Gx(E), so Gx(E) could be used to design spectral power distributions of museum lighting at a low illuminance. (3) The damage coefficient of LED-RGB was the same or smaller than that of fluorescent and halogen lamps.
We concluded that an LED-RGB with 630 nm, 530 nm, and 470 nm had the maximum Gx(E), and it was an advantageous spectral distribution for art appreciation under low illuminance for the aspects of color appearance and damage.
We examined the possibility of further lowering the illuminance in public bath facilities. A questionnaire survey of public bath users was conducted to explore the significance of modern public bath facilities, and users' preferences for brightness were obtained. On the basis of the survey results, a lighting environment with a lower illuminance than before was experimentally constructed and put in place for 21 days in a public bath facility. The results showed that even for an outdoor bath with about 0.5 to 1 lux, users evaluated the brightness as exactly good, and the lighting environment was evaluated to be effective for relaxation and interaction with accompanying persons. We showed the new possibility of designing lighting environments that match the demands of users of public bath facilities.