In order to study the appearance of colors under mesopic vision in response to changes in the spectral distribution of light sources, we have validated our previously proposed model of color recognition characteristics based on the opponent color response function. First, we developed a wavelength tunable light that provides light sources with various spectral distributions. Next, we generated four white light sources with different spectral distributions using this tunable light and conducted an experiment to evaluate the change in color appearance under mesopic vision. Finally, the experimental results were compared with predictions made using the color recognition characteristic model based on the opponent color response. The predictions were in close agreement with the experimental results, indicating the effectiveness of the model.

In typical measurements of total luminous flux using an integrating sphere, non-uniformity of the spatial response distribution function (SRDF) inside the sphere can cause measurement errors. It is important to analyze the SRDF in order to evaluate any potential uncertainty of the integrating sphere measurements. If the SRDF can be quantified, it may be possible to reduce the measurement errors. Our findings in this study showed that when the light distribution of the test light sources are different, a difference in the total luminous flux measurement occurs due to the difference in the internal SRDF of the integrating sphere. We also found that it is possible to quantify the effect of SRDF on the total luminous flux measurement by examining the opening angle of the luminous intensity distribution of the light source.

With the rapid spread of the novel coronavirus (COVID-19) infection, the early establishment of safe and low-cost virus inactivation technology has become an urgent issue. We have developed a mobile ultraviolet (UV) irradiation device that uses a low-pressure mercury discharge lamp made of quartz glass with a total length of 1,000 mm. This device emits light at an emission peak of 254 nm and is designed for efficient and cost-effective virus inactivation in unmanned environments, such as conference rooms and private rooms in commercial facilities. To assess the effectiveness of our device, we used the private rooms of commercial facilities of various sizes as model rooms (S-room; 2,001 mm (W)×2,166 mm (D)×2,500 mm (H), M-room; 1,989 mm (W)×4,042 mm (D)×2,500 mm (H), L-room; 3,172 mm (W)×7,889 mm (D)×2,700 mm (H)). We temporarily installed an UV irradiation device in each room and irradiated the rooms with UV radiation for 7 min in the S-room and 10 min in the M-room. Due to the size of the L-room, the UV irradiation was performed from two places. After UV irradiation at one place for 15 min, the device was moved and re-irradiated for 15 min. To evaluate the bactericidal effect of our developed UV irradiation device on various surfaces within the room, such as walls, floors, and ceilings, we measured the inactivation rate of E. coli and verified the device's performance. The results showed the inactivation rate of E. coli was 99.90% or more, except in areas where direct UV irradiation was obstructed by furniture. In addition, even in areas where direct light from the UV irradiation device did not reach, such as furniture, we observed a decrease in the survival rate of E. coli due to reflection from the walls. On the basis of the above verification results, we confirmed that the developed device efficiently inactivates bacteria and viruses within rooms used by an unspecified number of people, such as conference rooms and commercial facilities, in a short amount of time.

This study proposes the installation of pendant lighting at a low position in a shared work space to alleviate any sense of awkwardness among strangers. First, the extent to which embarrassment around others could be reduced was investigated by installing pendant lighting at eye level. Next, conditions to reduce both the discomfort around others and discomfort from the lighting while varying the height and intensity of the light source were examined. The results showed that, considering the workability, it was appropriate to install the light with a brightness of 2500 cd/m² and a desk-top height of 26 cm. This new lighting method was then applied to a real university common study space. The finding showed that, although it was difficult to feel any effect of the lighting at first, many users felt that it eased their discomfort around others and made their work easier after spending more time in the environment.

A lighting design was implemented around the seawall in Kesennuma City, which took into account the surrounding illuminance and the sense of continuity between the sea and the city. The road surface illuminance and the luminance distribution of the entire field of view were measured from the inside of the seawall toward a hill, and the visibility of landscape elements related to evacuation was evaluated. In addition, a survey was conducted after setting the lighting environment at a low illuminance level, and a lighting method considering the balance of landscape elements in the field of view at the time of a natural disaster was examined. The results highlight the importance of creating light that matches the terrain; emphasizing slopes and stairs, reflecting the surface of the water, and aiding people in recognising the evacuation route, while suppressing the luminance of the entire field of view.