# A Review of Light Shelf Designs for Daylit Environments
## 3 Discussion  
Daylight exploitation can increase performance and users' satisfaction of a building. However, to effectively use natural light, greater consideration is required, as every building is a unique structure and requires a different design approach. Architectural shading/daylighting systems can deliver daylight and possibly can reduce energy consumption in buildings. Is it possible to compare different light shelf designs with each other? Although the answer could be positive, in practice, such a direct comparison is problematic on the component's level. As already mentioned, most of the building standards are oriented in the performance based approach, where specific targets for the whole building are set. Consequently, the estimation of the light shelf's performance for either daylighting or energy consumption must always be performed in relation to the space in which they are placed. In practice, design teams use \"rules of thumb\" for the design of light shelves, an approach that can adversely affect their performance. Of course, a simulation analysis could lead to an optimal solution given that there is a budget for this. Since the light shelves are integrated into the facade, they are subject to the building code restrictions as far as their dimensions are concerned. In many cases, light shelves are actually part of the building structure, making the determination of their cost effectiveness difficult. According to our review results, there is no paper which investigates the cost optimal analysis for the light shelves. For the determination of cost-effectiveness, a life cycle analysis is needed where all costs related to the light shelf (initial, installation, operation, maintenance and disposal) are evaluated over its economic life. Conventional external flat light shelves can cost approximately \(\sim\)100 $ per m\({}^{2}\)[72]. Depending on the geometric form of the light shelf and the finish of the upper surface, costs can vary widely. In general, light shelves are not standard products since external light shelves are designed as part of the building facade. However internal ones are today available in prefabricated modules [73; 74; 75; 76].  
This paper provides an overview of the research realized on light shelves over the last 34 years examining forty papers which address the daylight impacts of light shelves in the built environment. In the majority (92%) of the cases reviewed, a south oriented open-plan office space having depth ranging from 5 m to 9 m was considered with ceiling heights between 2.7 and 3.5 m and window-to-wall Ratio between 10% and 100% under climates with high sunlight availability. In a small percentage (18%) of the cases, there was an assessment of the light shelf performance in a full-scale mockup since computer simulations or experiments with scale models are considered as accurate and cost-effective approaches. However, the simulation results should be viewed with caution especially when a geometrically and optically complicated design is used as these require validation against scale model  
Figure 15: Operation principle of the VARLA system presented in [71].  
measurements. Horizontal shelves are assessed more frequently with 37% of the cases are dealt with curved forms. The majority (82%) of the systems examined in this review were static and it seems that the analysis of their dynamic behavior is quite limited.