# A Review of Light Shelf Designs for Daylit Environments
## 2 Overview
### Performance Analysis of Curved Light Shelves
The reason for that is the reduced amount of natural light that is brought into the indoor space via reflection due to the perforation of the light shelf. However, lighting energy consumption is reduced when the results of the previously mentioned cases are compared with that from the case without any shelf. [PERSON] and [PERSON] [61] presented a performance analysis of three anidolic daylighting systems installed in a 6.55 m deep space in Lausanne (Latitude: 46.51\({}^{\circ}\)). One of them was an integrated system as illustrated in Figure 10, which was assessed using simulations for two types of ceiling (flat and slanted). In both cases, the system shows an increase in daylight factors in comparison to a reference facade with conventional double glazing. In the deepest part of the room, the increase in daylight factors was 1.4 times the value of the reference case when there was no external obstruction and 1.7 when an urban environment was simulated. Figure 9: Schematic representation of the cases examined in [56]. Another work dealing with the modification of the ceiling geometry is that of [PERSON] et al. (2018). In this paper, the authors studied the interaction between various ceiling geometries with a light shelf, using experiments with scale models and Radiance simulations in a deep side-lighted space. Various ceiling configurations were tested including curved, chamfered, sloped upward from the window, and sloped downward from the window. The evaluation of the light shelf performance due to modified ceiling geometries is based on the calculation of illuminance levels and the uniformity on the working plane. The scale model used represents a south oriented room in Irbid, Jordan (Latitude: 32.55\({}^{\circ}\)) with dimensions 6 \(\times\) 8 m with a ceiling height of 3.25 m and a window-to-wall Ratio of 40% located). The illuminance levels increased in the rear part of the room by 21-36% and decreased by 20-55% in the front when a curved or chamfered ceiling is used. When changing the ceiling surface reflectance type to specular, a further increase in illuminance levels at the back of the room was observed. This increase is 52% and 30% for curved and chamfered ceilings respectively in comparison with the illuminance values estimated for a flat ceiling. In addition, the illuminance level at the front of the room was reduced by 27% and 30% for curved and chamfered ceilings, respectively. In general, the best ceiling shape in terms of daylight levels and uniformity was curved. Extending his previous work, [PERSON] (2018) examined in this paper the combination of curved ceilings with a number of curved light shelves (Figure 11). The south oriented room used for the simulations was 8 \(\times\) 6 m with ceiling height 3.25 m and window-to-wall Ratio of 35.8%. Both external curved and chamfered exterior light shelves performed better when a curved ceiling is used. In addition, uniformity was improved compared to a horizontal light shelf. Figure 11: Light shelf designs examined in (2018). Figure 10: Schematic representation of an anidic daylighting system as examined in (2018). [PERSON] et al. [64] examined light shelf performance in a meniscus glazing panel. It's thickness and curvature angle were the parameters studied which affected its performance. The results, after a simulation of a South oriented room in Hong Kong, China (Latitude: 22.39\({}^{\circ}\) N) with dimensions of 10 \(\times\) 15 m and a ceiling height of 3 m with window-to-wall Ratio of 52% are as follows. The meniscus glazing panel enhances the illuminance in summer, and reduces it in winter, while the opposite happens with uniformity. An increase in illuminance is observed when the curvature angle ranges from 0\({}^{\circ}\) to 44.3\({}^{\circ}\) at high solar altitudes, and between 44.3\({}^{\circ}\) and 90\({}^{\circ}\) for low solar altitudes.