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.
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.
In the field of tunnel lighting design, a linear relationship in double logarithmic plots with a slope of minus 0.5 has been widely referred to as the relation between average road surface luminance and the overall uniformity of road surface luminance with keeping object visibility constant. This indicates that if the uniformity of road surface luminance is increased, the average road surface luminance could be lowered while maintaining object visibility at a certain level. Advancements in lighting technology, such as LED, have enabled highly uniform road surface luminance; however, lowering the average road surface luminance is a concern given the increase in elderly drivers. In this study, the relation between average road surface luminance and the uniformity of road surface luminance was investigated for young and elderly observers over a range of low to high uniformity. Our results indicate a non-linear relation in double logarithmic plots, especially in the low road surface luminance and high uniformity region. Furthermore, a marked increase in average road surface luminance is necessary for elderly observers to maintain the same visibility level as that of young observers.
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.
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.
Integrating sphere (IS) is commonly used to measure the total luminous flux emitted from a light source.Although the spatial response inside IS should be theoretically uniform regardless of the location of the IS, due to the dusts and some other causes, the spatial response distribution function (SRDF) of IS is not uniform.This nonuniformity mediates non-uniform distribution of the illuminance.For the light source has a planar configuration such as Organic LED (OLED) panel, this nonuniform SRDF might be affected to the total luminous flux depending on the size of the light source.Moreover, the larger the difference of SRDF inside IS, the larger the measurement errors.In this research, we assume the reflectance of the hemisphere walls to be uniform, and that the difference between two hemispheres were changed.Our simulation results show that the larger the size of the light source, the larger the effects on the total luminous flux.When the reflectance of the lower hemisphere is lower than 90%, the effects of the size are evident.
Luminance-based visibility evaluation methods can enhance lighting design flexibility in near future, in which case edge detection technologies will be essential. We developed an edge detection method by including a normalization algorithm based on neurophysiology and validated it by examining the relationship to subjective evaluation in tunnel spaces. The result showed that the algorithm in this research could estimate the visibility with sufficient accuracy. In the future, this algorithm will need to be combined with the optical mechanism in visual systems and compared with other algorithms with different parameters settings to further validate this method.
Road-projection technology has been developed to improve traffic safety, in which symbols or patterns are projected onto the road surface from a vehicle. The response times of cyclists when a vehicle direction indicator flash with and without road-projection were obtained to verify alerting effects of the road-projection lamp linked to the direction-indicator of the vehicle. When cyclists could not see the direction-indicator lamp flashing on the vehicle or when they were moving by a bicycle, the response times with road-projection were shorter than those without it. Favorable responses were received from participants through the questionnaire used in this study regarding the road projection of the direction-indicator. Even when cyclists were operating smartphones, the response times with road-projection were shorter than without it. However, this suggested that delays caused by operating smartphones were longer than the time saved by road-projection.
Luminance-based visibility evaluation methods can enhance lighting design flexibility in near future, in which case edge detection technologies will be essential. We developed an edge detection method by including a normalization algorithm based on neurophysiology and validated it by examining the relationship to subjective evaluation in tunnel spaces. The result showed that the algorithm in this research could estimate the visibility with sufficient accuracy. In the future, this algorithm will need to be combined with the optical mechanism in visual systems and compared with other algorithms with different parameters settings to further validate this method.
A viral fluid containing coronavirus OC43 was smeared onto plastic surfaces and irradiated with light at wavelengths of 222, 254, and 275 nm emitted by an excimer lamp, an ultraviolet lamp, and a deep ultraviolet LED, respectively. After irradiation at varying durations, the virus on the plastic surface was collected and the viral activity was measured to compare the viral inactivation capabilities of the three wavelengths. We found that the 275-nm light from the deep ultraviolet LED exhibited an inactivating effect greater than or equal to the 254-nm light from the UV lamp that is used as a sterilizing device in general applications. The results demonstrated the potential of deep ultraviolet LED irradiation for general viral infection control and in the ongoing fight against the novel coronavirus, SARS-CoV-2.
The overall lightness of the whole surface of a fabric under non-uniform and uniform lighting conditions was investigated. In the experiment, the perceived lightness of the bright, dark, and whole area of pieces of glossy and matte fabric placed on a pseudo-sine-wave board under different combinations of directional and diffused lights was measured by matching the lightness to a reference grayscale placed in the matching box with a diffused light. The perceived lightness of the bright and dark areas could be expressed with a linear function of the logarithmic luminance of each area for both the glossy and matte fabrics. The perceived overall lightness under the non-uniform lighting conditions with directional light was close to that of the dark area with no significant contribution of the lightness of the bright area. This is consistent with the previous study which showed the elimination of highlights in the lightness judgment. However, contribution of the bright area was not nothing because it raised the perceived lightness value about 1.2 times higher than that of the dark area. On the other hand, the overall lightness under the uniform lighting condition with diffused light only was estimated by the weighing sum of the perceived lightness of bright and dark areas. Further investigation into the effects of spotlight size, its luminance, luminance contrast between the bright and dark areas, and the glossiness of fabric is necessary.
High-power LED floodlights for sports stadiums such as baseball and soccer stadiums have become increasingly popular and have already been installed in many facilities. LED floodlights consist of many LED chips that each have a small and high luminance light-emitting surface. Therefore, when a ball overlaps with the lighting fixture in a player’s visual field, a temporal vision loss due to the afterimage of an intense light-emitting surface, i.e., disability glare, occurs together with an excessive discomfort glare.
We evaluated the spectroscopic performance of an otoscope during otoscopic examinations using a headlight with an LED source. We used the mechanisms and the specifications of the objects measured with the otoscope and so on to evaluate the spectroscopic performance. Experimental equipment was built using the existing otoscope and headlight, and we demonstrated methods of measuring the spectral irradiance of the otoscope. We demonstrated methods of evaluating the spectroscopic performance using the spectral irradiance ratio and chromaticity by the measured spectral irradiance. We measured the spectral irradiance of the otoscope using the measuring methods. We found that the spectral irradiance distribution in the otoscope is greatly affected by the spectral distribution in the headlight source. We evaluated the spectroscopic performance of the otoscope using the evaluation methods. The spectroscopic performances of the reflected light onto the surface of, and the direct and reflected lights in, the otoscope differ and are affected by differences in shape, surface condition, length, and the diameter of the wide mouth. The spectroscopic performance of the direct and reflected lights in the otoscope is affected by differences in the diameter of a narrow mouth and the distance and angle between the otoscope and the headlight.
