Effectiveness of adjustable light shelf to improve luminous environment of reading space in libraries considering sky conditions of Dhaka

Abstract

Efficiency in university libraries is considered more important than at any ordinary library.As an important place for students to read and study, the quality of lighting in the reading space of university library has a great influence on the visual and learning efficiency of students. A common phenomenon in the reading space of libraries are students more tend to draw the curtain when the weather is sunnier than usual, and turn on the artificial lighting, resulting in greater waste of energy. The natural lighting design of reading space in libraries not only affects the physical and mental health of readers, but also concerns the energy consumption of the libraries. The capital city Dhaka is one of the mega cities of the world. Most of the public and private university libraries in Dhaka lack the standard illumination and glare free uniform lighting in the reading spaces.

Light shelves have been discussed in numerous studies as suitable solutions for controlling daylight in side-lit spaces. The light in a library must be adequate for the users to see a particular task, usually reading a book or the text on a computer screen. Studies show, in a tropical location, such as Bangladesh, the introduction of light shelf at any height produces an overall reduction of illumination on the work plane throughout the interior space; however, light shelf can be an effective element to enhance the quality of daylight in tropical buildings, if designed and located properly. This research aims to identify the effectiveness of adjustable light shelf for university library windows to ensure standard daylighting for reading activities throughout the year, and during different seasons considering regional and climatic context of Dhaka. At first, the literature review was conducted to get the fundamental knowledge, in order to select the angles of light shelves for the simulation study. Then field survey was done to figure out the problem in the reading space of the university libraries and a case reading space was selected.Then dynamic annual Climate Based Daylighting Modelling (CBDM) method was used to evaluate the performances of different light shelf angles throughout the year and during different seasons considering all weather sky luminance models (i.e. DAYSIM). Finally, the results were compared to find out most effective angle of light shelf in a reading space of a library throughout the year and during different seasons in context of Dhaka.

Results indicate that, angular light shelves in the south façade windows increases the uniformity of illuminane in the reading space of a library. The adjustable light shelves are effective in creating a uniform luminous environment in reading space of a library under overcast sky condition as Dhaka. An optimum angle of 30° light shelf provides better luminous environment throughout the year in a reading space in context of Dhaka. On the other hand, for different seasons of the year, different angles of light shelves were found, as 25° for 20th March,20° for 21st June, 30° for 22nd September and 35° for 21st December through dynamic daylight simulation of a reading space in a university library in the context of Dhaka. It is expected that the findings of this research will help the architects and the designers to design effective library building windows with angular light shelves in terms of daylighting the reading spaces.