Search

An essential impact which can improve the indoor environment and save on power consumption for artificial lighting is utilization of daylight. Optical fiber daylighting technology offers a way to use direct daylight for remote spaces in a building. However, the existing paradigm based on the precise orientation of sunlight concentrator toward the Sun is very costly and difficult to install on the roof of buildings. Here, we explore an alternative approach using mirror-coated lens array and planar waveguide to develop a flat optical fiber daylighting system (optical fiber daylighting panel) with lateral displacement Sun-tracking mechanism. Sunlight collected and reflected by each mirror-coated lens in a rectangular lens array is coupled into a planar waveguide using cone prisms placed at each lens focus. This geometry yields a thin, flat profile for Sunlight concentrator. Our proposed concentrating panel can be achieved with 35 mm thickness while the concentrator's width and length are 500 mm × 500 mm. The commercial optical simulation tool (LightToolsTM) was used to develop the simulation models and analyze the system performance. Simulation results based on the designed system demonstrated an optical efficiency of 51.4% at a concentration ratio of 125. The system can support utilizing a lateral displacement Sun-tracking system, which allows for replacing bulky and robust conventional rotational Sun-tracking systems. This study shows a feasibility of a compact and inexpensive optical fiber daylighting system to be installed on the roof of buildings. [ABSTRACT FROM AUTHOR]

Light pipes can provide daylight and improve lighting conditions in buildings. Knowledge of their optical performance is a prerequisite for their successful integration into buildings. This article presents and analyses the experimental performance and the specific efficiency characteristics of a light pipe as integrated into an experimental test-cell. Extensive measurements are performed for eight continuous months under clear, cloudy and intermediate sky conditions. The spatial and temporal variability of the indoor illuminance is analysed using clustering techniques. It is found that there is an almost exponential relation between the average and the maximum indoor illuminance with the exterior illuminance levels. In parallel, a strong spatial inhomogeneity is observed under all sky conditions. The transmissivity or Daylight Penetration Factor of the light pipe is found to present a strong daily variation during the clear days while it was almost constant under cloudy sky condtions. A clear correlation of the light pipe’s Daylight Penetration Factor is found against the solar azimuh and solar altitude especially under clear sky conditions. [ABSTRACT FROM AUTHOR]

We introduce a way to simultaneously measure the light density, light vector and diffuseness of the light field using a cubic illumination meter based on the spherical harmonics representation of the light field. This approach was applied to six light probe images of natural scenes and four real scenes built in our laboratory, and the results were compared to those obtained using Cuttle’s method. We also demonstrated a way to simultaneously and intuitively visualise the global structure of the light distribution using light tubes and colour coding for the light density, light flow and diffuseness variations through the space. Together with Mury’s work, we have a complete way to describe, measure and visualise the local and global low-order properties of light distributions in three-dimensional spaces. [ABSTRACT FROM AUTHOR]

A coupled system consisting on a heliostat and a matrix of light-pipes inside one road tunnel where the heliostat injects sunlight, is proposed. Its reliability and efficiency from theoretical calculations and a mock-up, is analyzed as a function of tunnel orientation. The heliostat is fixed above the road some meters before the portal gate of the road tunnels. It continuously seeks the correct orientation so that the angle between sun, heliostat and light-pipes in the portal gate, injects of parallel sunrays every moment. Then, these rays are guided through the light-pipes and distributed on the road in the threshold zone with a remarkable improvement of the efficacy of light-pipes and the relevant savings in electrical consumption and number of luminaries. The results of calculations and measurements on mock-up, that show energy savings above 20% in the most favorable tunnel orientations and 14% in arbitrary orientations, as well as a discussion about the most accurate tunnel orientations are analyzed and presented. [ABSTRACT FROM AUTHOR]

Double loaded corridors in educational buildings generally experience a low daylight level, as they do not have enough direct contact with the outdoor environment. The task light level in those corridors is lower than that in reading or office spaces. Double loaded corridors normally depend on artificial light. On the other hand, double loaded corridors need to be lit all the day during the occupation period as one can not specify when different users could use it. This research explores the possibility of using tubular light systems in addition to some architectural solutions to provide double loaded corridors with the required daylight. The research used anidolic, light pipe and ceiling cavity systems in addition to high windows from side offices to improve daylighting in double loaded corridors. The experimental study, which has taken place at JUST, showed that anidolic systems could provide double loaded corridors with sufficient lighting levels. On the other hand, radiance simulations showed that anidolic and some other solution systems can provide corridors with sufficient daylight in lower floors, while light pipes can provide corridors with sufficient daylight in upper floors. [ABSTRACT FROM AUTHOR]

Abstract: Approximately, 20% of the electricity consumed in the world is spent for lighting. More efficient utilization of the sun, as a natural source of light, for lighting would save electricity used for lighting. The aim of this study is to illuminate a windowless room via a light-pipe and dimmable electronic ballasts. Light-pipe is used for the illumination of the space during the daytime. In case of inadequate daylight, artificial lighting is made via dimmable electronic ballasts and fluorescence lamps. Artificial lighting is supervised by a fuzzy logic control system to keep the illumination level at 350lux. When there is a motion in the room, the system works with the message of the motion sensor, which, thereby, enables energy saving. Additionally, dimming the lamps result in conversation of the electrical energy used for illumination. After the experimental studies, 350lux value targeted in the work plane is achieved with ±10lux error. [Copyright &y& Elsevier]

Abstract: Tubular daylight-guidance systems are linear devices that channel daylight into the core of a building. The development, over the last decade, of materials with high specular reflectance has led to a large number of passive zenithal systems; the most commercially successful type of daylight guidance being installed in many parts of the world. The rapid change in technology has not been matched by the development of either reliable and standardised design methods or design criteria against which the systems may be evaluated. This paper presents the results of several surveys of daylight guidance systems in 13 working buildings. These give an indication of the conditions created, which are used as the bases of suggested design criteria. A critical review of existing performance prediction methods notes that these lag far behind comparable methods for electric lighting and conventional glazing. A number of improved methods of prediction, currently under consideration by the CIE Technical Committee TC3-38, are presented and each is tested against measured data from the installation surveys. [Copyright &y& Elsevier]

Abstract: There are now several ways of predicting the illuminance produced for different configurations of light pipe. This study is an overview of two such methods for two slightly different forms of light pipe diffuser. Both models are partly empirical in nature but have been formulated using significantly different techniques. Their outputs are also different in presentation, although both models deal with illuminance predictions (with one of the models offering luminous flux predictions also). The models have also used separately obtained measurements in their formulation and so can be seen as being two independent methods, using similar logic, to achieve similar goals. While the two sets of predictions cannot be compared to each other directly (due to the difference in diffuser in each case), the two models can be presented as an indication as to how modelling procedures of this type can be approached. [Copyright &y& Elsevier]

Abstract: Light pipes are simple means of directing daylight (diffuse and direct light) into interior spaces. Previous work by the authors described the initial work on a luminous flux and illuminance predictive model for straight light pipes, using a basic equation for illuminance distribution as a function of horizontal distance. Further work has now produced a model that uses the cosine law of illuminance to describe the distribution of light from the light pipe diffuser as well as takes into account pipe elbow pieces or bends. The resulting illuminance model can be described as a quartic cosine model. By producing a “luxplot” prediction for any given light pipe application, it is possible to maximise the potential of these daylight providers and design their configuration to suit any given need. As part of this study, wide-ranging illuminance and luminous flux data were collected both for the formulation of this model (as the formula is semi-empirical) and its validation. [Copyright &y& Elsevier]