# A Review of Light Shelf Designs for Daylit Environments
## 2 Overview
### Performance Analysis of Flat Tilted Light Shelves  
[PERSON] and [PERSON] [49] examined a number of parameters using simulation: the external light shelf depth varied from 0.3 m to 1.2 m, the internal shelves width varied from 0 m to 1 m, while their slope angle was set equal to 0\({}^{\circ}\), 5\({}^{\circ}\), 10\({}^{\circ}\), 20\({}^{\circ}\) and 30\({}^{\circ}\). The educational space was in Tehran, Iran (Latitude: 35.68\({}^{\circ}\)), with dimensions of 7 \(\times\) 8 m, with 3.5 m ceiling height and a WWR of 50% and all cardinal orientations were simulated. The results showed that for the south orientation, increased light shelf dimensions result in an increase of the area of the work plane with suitable daylight levels while glare was reduced when compared with the space without the light shelf installed. It seems that horizontal external light shelves are more efficient than those that have a slope angle of 30\({}^{\circ}\). For north orientations, the lack of direct sunlight penetration resulted in a poorer daylight performance  
Figure 8: Schematic representation of the cases studies that have been examined in [44].  
of the space when a light shelf is installed. As the light shelves' internal and external depth increased, daylight illuminance decreased while their slope angle did not have any significant impact. The results were nearly identical for the east and west orientations. Generally, the increase of the internal and external light shelf dimensions decreased areas that were over-lit, due to improving the shading of the window. The raise of the tilt angle of the shelf caused an increase in direct sunlight penetration which in turn hindered the daylight performance of the space.  
[PERSON] [50] suggested that the optimum upward slope angle of a light shelf painted white can be calculated using the equation for south oriented spaces:  
\[Slope\ Angle=40^{\circ}-\left(Latitud/2\right) \tag{4}\]  
and 15\({}^{\circ}\) for east and west orientation.  
[PERSON] [51] studied a south oriented typical classroom in Athens, Greece (Latitude: 37.98\({}^{\circ}\)) using simulation. The model used for the simulation was validated by comparing daylight factors estimated by simulation and measurements from an actual classroom. The facade system consists of a light shelf and semi-transparent movable external blinds. The results indicate that the best case in terms of increased daylight illuminance levels and glare reduction is the one with the external light shelf installed at 2 m from the floor, and a depth of 0.80 m \(\pm\) 0.20 m and a tilt angle between 10\({}^{\circ}\) and 20\({}^{\circ}\) with a reflectance equal to 90%. The use of a reflective light shelf to reduce glare problems and redistribute daylight in an educational open-plan studio space was investigated by [PERSON] [52]. In this research, several tilt angles of a light shelf installed on the north facade were examined along with other design parameters, such as the height of the light shelf and the slope of the ceiling. The average value of the daylight factor for the base case was 30.28%. For the sloped ceiling case the avg. value for the daylight factor was 29.24% and the daylighting levels in most points lower than 1 m in the studio were less than 2000 lx. Though sloping the ceiling did not generally make much difference, more even distribution of daylight factor levels across the height of the space was observed. The results indicate that 5\({}^{\circ}\) sloped ceiling together with a slope angle for a light shelf equal to 60\({}^{\circ}\), helped to reduce the illuminance differences between the ceiling and the back wall.