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.
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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