Energy and Buildings 116 (2016) 190–205 Contents lists available at ScienceDirect Energy and Buildings j ourna l ho me pa g e: www.elsevier.com/locate/enbuild Evaluating daylight performance of light shelves combined with external blinds in south-facing classrooms in Athens, Greece Aik. Meresi ∗ Hellenic Open University, Greece a r t i c l e i n f o Article history: Received 10 April 2015 Received in revised form 28 November 2015 Accepted 8 January 2016 Available online 9 January 2016 Keywords: Daylight Classrooms Light shelf Shading devices Visual comfort Greece a b s t r a c t The contribution of daylight to energy efficient building design and to the creation of a pleasant environ- ment that provides visual comfort to its users has been a subject of study for years. This paper addresses the way in which daylight can be efficiently used in a typical classroom in Athens, Greece, by improving its distribution in the space and providing shade. Based on the conclusions drawn from the literature review, the system that is chosen for study consists of a light shelf (for shading and light redirection) and semi-transparent movable external blinds (for more shading, adjusted to the occupants’ needs), which are mounted on the glazing of a south-facing classroom. The experimental study consists of six stages, all performed in Radiance software. The individual results and conclusions lead to the definition of the optimum characteristics of the system, including the light shelf’s width, mounting height, inclination and reflection index, which upgrade the daylight performance in the space under study. © 2016 Elsevier B.V. All rights reserved. 1. Introduction The study of daylighting in school buildings has been a subject of interest for many years. In fact, daylight has played a crucial role in the design of educational spaces, perhaps more than in the design of any other building type [1,2]. Studies have shown that good daylight in schools is able to create a pleasant environment [3], enhance academic performance [4,5], promote better health [3] and provide significant energy savings [6], especially when com- bined with daylight responsive control systems [7]. For all of these reasons, the importance of daylight in schools is internationally recognized today and daylight use is a crucial design parameter for architects. The assessment criteria for daylighting in schools are mainly qualitative. Although the proposed lighting levels are different in every country [1,8], 300 lx and 2% Daylight Factor (DF) are some common minimum standards for schools. In Greece, the Hellenic School Buildings Organization SA promotes qualitative criteria over quantitative: uniformity of daylight distribution, exploitation of diffuse light from the sky, glare avoidance and, if possible, use of a daylight responsive control system [9]. The uniformity of daylight distribution in a space is of great importance not only because it affects glare but also because researchers argue that it is related to ∗ Correspondence to: Archelaou 14, 60200 Litochoro, Greece. E-mail address: katmeresi@yahoo.gr the probability of occupants switching on artificial lights [10]. In fact, people find a room brighter when it is uniformly daylit even if the amount of light is less [11] because, according to Hunt [10], the appearance of a space is governed by its darkest parts and their contrast to the lightest parts. In Greece, little research has been done in this field. A relevant study [12] combined both objective observations and subjective reporting by the occupants in twenty classrooms in three different Greek towns to identify the side effects of daylight use and sunlight penetration in classrooms, such as the annoying presence of sun- light on the desks and the extensive use of curtains. Some of the most important conclusions of this study are as follows: - There were no correctly designed shading devices in any of the schools studied. - Except for cases with external obstacles, the incoming light was sufficient but was not well distributed (poor illuminance unifor- mity). - In dense urban environments, the blocks of flats opposite the classrooms significantly lowered the internal daylight levels. - On sunny days, when curtains were used to prevent heat gain and/or glare, the daylight levels fell so far that electric lights were needed. - Sunlight falling on the desks or on the blackboard was disturbing for the majority of the students, and those that were disturbed pulled the curtains to avoid the sun. http://dx.doi.org/10.1016/j.enbuild.2016.01.009 0378-7788/© 2016 Elsevier B.V. All rights reserved.