It is widely known that light exposure during the daytime, onset of sleep, and during sleep affects the circadian rhythm and the quality of sleep.However, the indices of light environment such as illuminance and color temperature used in such discussions are based on the visual characteristics in a bright place such as daytime with the eyes open.That is, in order to appropriately grasp the light environment during sleep with the eyes closed, it is necessary to know how to perceive brightness when the eyes are closed and the light transmittance of the eyelids.

　However, in the previous research, the lighting environment was very different from the lighting environment in daily life, such as extremely low illuminance and evaluation with only one eye.Therefore, in this study, we adopted an experimental method using a lighting device that increases or decreases the illuminance according to the opening and closing of both eyes under the condition that the entire face (both eyes) is illuminated relatively brightly (illuminance 100 lx).A total of 33 subjects were asked to adjust the brightness of the light by themselves so that the perceived brightness when the eyes were open and when the eyes were closed matched. Calculated.

　The results revealed that the light transmittance of the eyelids was several to ten times higher than the light transmittance in previous studies.In other words, the perceived brightness of illumination with closed eyes may be significantly higher than previously thought.In addition, it was found that the color of the light source makes a big difference, and red light feels brighter, while blue light feels darker.

　The results of this research are expected to contribute to research on lighting suitable for sleep in various situations such as naps, late-night traffic, and disaster shelters, as well as when falling asleep.

Paper information:[Color Research and Application] Perception of brightness when the eyes are closed