عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Daylight is an essential resource that is readily available and unlikely to run out through an unforeseeable future. Lighting affects the appearance of a place, its occupants’ mood and productivity level. Daylighting is chosen to save energy, avoid adverse health effects of over-illumination by artificial lights, and also for aesthetics matters. By careful usage of natural light and the appropriate control of electric light, saving important energies can be achieved. Daylight presence in buildings is vital for people, therefore daylighting should respond to their visual and perceptual needs. Visual comfort is multidimensional; it is not sufficient to simply provide adequate illumination levels. Visual perception is the most developed sense of ours so for its comfort, glare must be controlled and patterns of contrast should be appropriate. Many innovative daylight devices have been invented that have different functions, such as light guiding, light transport and light diffracting systems. Light shelf is a direct light guiding system that is attached to a window. Light guiding systems refract and reflect sunlight to deeper parts of a place. Light shelf is considered as one of the most efficient solutions for the light energy issues. It is a part installed horizontally or with a slope way up a window to control and redistribute incoming sunlight and daylight. Light shelf improves the uniformity of daylight in a room by reflecting light into the building from its upper surface, while it provides solar shading and decreases glare. According to these features and also appropriate price and the quality that does not hinder the vision, it has been made with an eligible technology. Using light shelves decrease energy consumption. There are many kinds of light shelves based on their features, such as dimension, proportion, slope, material, geometry and form (rectangular, curved, etc.), their combination with other devices (such as solar shadings), being installed interior, exterior or both, being single or multiple, static or dynamic and effect of interior spaces (such as ceiling height or slope) and other matters, these variety of typologies makes it hard to choose the best alternative for any particular situation. Researches about light shelves began in the early 1950s. After a while many experts tended to know much about such systems and various studies have been conducted. This paper reviews the publications that discussed light shelves during recent years -about 43 papers and books- then classifies the light shelves and finds out about the exploration of each field. Three categories of research method, research questions and building functions have been surveyed in these researches. 1. Research method has been categorized to make model and test it under actual sky or artificial sky, computer simulation (such as Radiance, Daysim, Diva, etc.), post occupancy evaluation (POE) and evaluation of light shelf productivity in actual situations, and mathematical calculations. 2. Research questions have been categorized into introduction of a new method, comparison light shelf with other devices, light shelf efficiency, light shelf material, types of light shelves, and space proportion effects on light shelf function, new or combinative light shelves. 3. Building functions have been categorized into residential, office, commercial, educational and unknown. The review reveals that 35% of researches are based on computer simulation and this method has been developed and used more in recent years. Data calibration with two or three methods assures the researcher of the results. Making a model stands at the second position and simulation and making a model together is the third one. About 30% of researches were conducted on office buildings and that shows the importance of daylighting in such kind of properties. Educational spaces were the next one. Unfortunately many researches were operated on hypothetical spaces without any specific usage. It was clear that a large amount of researches were based on comparing of light shelves with other appliances and the results show that light shelves have a popularity and good qualification among other daylight technologies. After that surveying different features of light shelves have been tested. To control glare, light shelves can be used in combination with other devices, and to find the optimum case, all variables should be considered. Dynamic light shelves and new combinational devices are at the beginning of their way and it seems fulfilling as the advancement of science introduces and develops new systems. Finally, the use of light shelves is according to illuminate a space which should be integrated with the electric lighting system.
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