# A Review of Light Shelf Designs for Daylit Environments
## 2 Overview
### Performance Analysis of Static Horizontal Light Shelves
The South oriented space had dimensions of 10 \(\times\) 15 m and a ceiling height of 3 m and was located in Toronto, Canada (Latitude: 43.65\({}^{\circ}\) N). The optimal length and depth of the shelves was calculated based on the following parameters: the window head height, the still height, the height of the light shelf, the wall thickness and the sun position (solar altitude and solar azimuth). The results showed that in the context of analysis, light shelves increased the useful daylight illuminance values mainly in the first 6 m from the windows and provided a more uniform distribution of daylight. This study indicated that narrow full-height windows provide better daylighting compared to shorter but wider windows and, light shelves have no benefits when applied to windows not facing South. Furthermore, the study showed that regardless of the window geometry, light shelves enhance daylighting especially in the front zone and especially for South facades. The maximum level of UDI for cases without light shelves occurred at 3 m, 4 m, 5.5 m and 6 m away from the windows, when window-to-wall Ratio is 25%, 35%, 45% and 55%, respectively. The presence of the light shelf decreases a bit the above-mentioned distances to 2.5 m, 3.5 m, 4 m and 5.5 m. The final design of the light shelves had a height of 2.25 m from the floor with the reflectance set at 80%. [PERSON] and [PERSON] [41] performed a daylight analysis of a deep meeting room equipped with a light shelf using radiance simulations. The room is located in Haifa (Latitude: 32.5\({}^{\circ}\) N). Three systems have been examined: a single window without any external protection, a horizontal light shelf and an anidic concentrator. The dimensions of the simulated light shelf are presented in Figure 6.  
Figure 5: Light shelf dimensions and vertical shade angle as examined in [39]. The results indicate that the light shelf provides a safer approach to the problem of daylight penetration, reducing contrast between areas near the window and those at the back of the room, by sacrificing illuminance levels. The illuminance values beyond the daylight zone that exceeded 300 lx was 1.5-2 times higher when compared with the reference case. In addition, the light shelf had maximum efficiency when the sun shone directly over it, while its effectiveness is reduced at distances more than 6-7 m from the window. The anidolic system was found to increase lighting levels throughout the room for all orientations. [PERSON] et al. [42] performed a series of daylight simulations in Dhaka, Bangladesh (Latitude: 23.8\({}^{\circ}\)) of horizontal combined (exterior and interior) light shelves with a depth of 0.5 m in both directions and an upper surface diffuse reflectance equal to 88%. The analysis parameter was the light self's height from the floor under overcast sky conditions. Figure 7 illustrates the cases that were taken into consideration. Again, as noted in other studies, the average illumination is higher in the case without the use of a light shelf, while the uniformity is better. The daylight levels calculated for the case w/o the light shelf installed were on the average 650 lx, but with uneven distribution. For the cases with the light shelves the max avg. value (478 lx) was observed for the highest configuration (2.75 m above  
Figure 6: Examined light shelf configuration with the main dimensions [41]. Figure 7: Extended lightshelf with equal depths for the internal and external shelf (0.5 m) and variable heights that were examined [42]. the floor level), and the min. at 2 m height. In the deeper areas, the effect of light shelf height on the illumination levels was not as significant due to overcast sky conditions. However, brightest interior ceilings were recorded for a light shelf at a height of 2 m and darkest for a light shelf at a height of 2.5 m. The results indicate that light shelf with a height of 2 m from the floor level together with 3 m high ceilings performed better than other alternatives including a reference case, where no light shelf was present.