In recent years daylight harvesting has been one of the promising systems to reduce lighting energy consumptions. Usually in this system the lighting environment is taken into consideration by securing the horizontal surface illuminance on the desktop using photosensors on the ceiling, however, it has become clear in some studies that the quality of the lighting environment does not always link with the desktop illuminance, and luminance distribution at the occupant's eye or vertical illuminances are more important for evaluating the lighting qualities. Therefore, in this research, we aim to develop a new method for daylight harvesting systems by measuring ceiling and window luminance using simple photosensors. The goal of this system is to secure appropriate spatial brightness in the office space and to improve energy efficiency performance at the same time. In this paper simple formulae for estimating spatial brightness in offices with windows were obtained.
The purpose of this study is to verify whether the spatial brightness of the real space can be reproduced using the high-luminance large screen display. Firstly, we conducted the subjective experiment in the real space. Next, the linear scaling images to present on the high-luminance large screen display were made from luminance and chromaticity data measured in the real space. The maximum value presentable by the display was 1,200cd/m2, therefore, luminance above 1,200cd/m2 were blown out. Then, the subjective experiment was conducted using those images displayed on the large screen display. The spatial brightness was memorized and answered by adjusting the luminance inside the reference space, called “adjustment box”, so that the brightness in the box became the same as the one in the real space. From comparing the logarithmic values of the brightness evaluation of the real space and the one of the linear scaling images on the display, we found that the spatial brightness evaluation on the display roughly matched to the one of the real space. It was also suggested that there is a possibility that the effects of windows on the spatial brightness evaluation may be different between the real space and the two-dimensional display.
This study aims to verify the relationship between the spatial brightness evaluation and average luminance on a moving gaze point tracking by targeting offices with different luminance distributions. Subjects wearing eye-tracking devices evaluate the spatial brightness of the various light environments displayed on a large screen display. In the results, the tendency for gazing at the window is found to be high as compared to the other parts. The average luminance is calculated by integrating the time on the path of the moving gaze point. Furthermore, we analyse the relationship between the average luminance of each part of the light environment on the display and the brightness evaluation value. The average luminance considering the movement of the gaze point at the time of brightness evaluation has higher explanatory power,0.305, for the spatial brightness than the average luminance,0.259, in the entire visual field area. In contrast, the explanatory power of brightness evaluation was not improved drastically, even considering the gazing time and luminance. In future, the relationship between the evaluation of the spatial brightness and the gaze point/gaze time can be analysed by considering the absolute value of the luminance of the window surface and the luminance ratio with the surroundings.
In recent years, both the quality of the light environment and the reduction of lighting energy are required in offices. To realize these requirements, it is effective to reduce the illumination of background area where occupants are absent while keeping the brightness of the task area where occupants are present. In this study, we conducted a subjective evaluation of spatial brightness in a non-uniform lighting environment based on the European standard and in a uniform lighting environment. In the experiment, the satisfaction of the whole lighting environment was taken as a superordinate concept, and the absolute level of brightness, visibility, the appropriateness of brightness, and non-uniformity were evaluated as factors explaining the satisfaction. As a result, in the non-uniform lighting environment in conformity of the European standard, while visibility and absolute brightness levels around desktops were highly evaluated, the level of satisfaction with light environment was low.
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