# A Review of Light Shelf Designs for Daylit Environments
## 2 Overview
### Performance Analysis of Curved Light Shelves  
We consider as advanced light shelves all shelves that either guide direct sunlight in the interior of a space or concentrate and redistribute diffuse daylight. In almost all cases highly reflective surfaces when used with static shelves have a more complicated geometrical form (i.e., anidolic), while the cases of dynamic shelves (i.e., sun tracking light shelves) need a control strategy to adjust their position in relation to the clecestory window. Thus, their operation is based on their rotation according either to the sun's position and aiming point on the ceiling [53] or to the lighting energy achieved [54]. In May 1996, [PERSON] et al. [55] proposed a highly reflective curved light shelf with a small inlet aperture capable of redirecting sunlight into depths of 9 m from the window wall. Scale model results proved that illuminance uniformity improved more than a typical diffusing hemisphere skylight. The system was installed in real scale where a number of visitors were polled for their opinion on visual comfort issues. The results were satisfactory. [PERSON] et al. [56] tested a number of light-shelf designs together with light pipes. This work was a continuation of a previous research [57]. In total, four systems were tested in Los Angeles (Latitude: 34\({}^{\circ}\) N) for south and east/west orientations. The light shelf designs that were tested are presented in Figure 9. The systems were designed using ray-tracing techniques and daylight measurements in scale models and then their behavior was simulated using the DOE 2.1E building energy analysis software. The room used for the study had a clecestory window of 0.5 m height while the room itself was 3 m high. Four light shelf designs were used: (a) a horizontal static exterior and interior (depth 1.1 m in total) whose upper surface had been painted white, (b) a single level curved light shelf with side reflectors whose surfaces had been covered with a specular reflector film, (c) a bi-level and, (d) a multi-level light shelf. The curved (b, c, d) configurations consisted of a segmented surface to redirect sunlight with changing solar altitudes. The inclination of each segment was computed by considering window orientation and site latitude, to ensure an optimal angle for redirection into the space. These segments were coated with a highly reflective thin film (reflectance 88%) that could produce two types of reflection: specular and narrow spread. The aperture area for the single level light shelf was 2.8% of the floor area and a working surface illuminance over 200 lx was achieved throughout a year from 10:30 to 13:30 at a distance of 8.4 m from the window under clear sky conditions. The bi-level light shelf has an aperture area more than twice that of the single level and achieves even higher illuminance levels than the base case. Overall, light shelf designs can increase interior daylight levels in a zone of between 4.6 and 9.1 m away from the window wall under clear skies with a rather small aperture area. Follow up studies were presented, further developing the aforesaid prototypes to improve daylighting performance at more oblique solar angles to the window [58; 59]. [PERSON] et al. [60] proposed perforated light shelves aiming at minimizing the effect of wind pressure when they are installed in high rise buildings. An actual-scale testbed was used to evaluate the performance in terms of lighting energy savings. The perforated light shelf was produced by punching holes of various shapes into the reflectors' surface. The parameters examined were the vent ratio which is defined as the ratio of the perforated area to the entire area of the shelf and the tilt angle of the shelf. The results show that increasing the vent ratio from 29.5% to 35.3% there is an increase of lighting energy consumption from 20.6% to 48.3% respectively, in comparison with the results from a case with a non-perforated light shelf.