# A Review of Light Shelf Designs for Daylit Environments
## 2 Overview
### Performance Analysis of Static Horizontal Light Shelves
In addition, there was a significant increase of the work-plane illuminance values ranging between 300-900 lx by 60% compared with the unshaded case. A study conducted by [PERSON] et al. (2014) evaluated the performance of various interior light shelves initially using scale models in Raleigh, North Carolina, USA (Latitude: 35.7\({}^{\circ}\) N). The data collected from the measurements were used to validate simulations performed on yearly basis using DAYSIM. The parameters examined were the depth of the light shelf, the ceiling height and, interior partitions typical of North American office building settings, in a multi-storey office building. The examined interior lengths of the shelf ranged from 0.6 m to 3.6 m with a step of 0.6 m while the height and interior kept the same. In the same manner the ceiling height was studied varying from 2.75 m to 3.65 m with 0.3 m step and the interior light shelf was set at 0.6 m. The results revealed that although light shelves generally enhance daylight in areas away from the opening, their performance is dependent on the cleststory area, and the ceiling height. Adding partitions that are either parallel or perpendicular to the South-facing window results in a major decrease of the illuminance values especially in areas away from the window. Among the six cases, the light shelf with 1.2 m depth performed better when compared with the alternatives, but an interior depth of 1.85 m appeared to be the optimal solution providing more shading by blocking direct sunlight. The increase of the ceiling illuminance resulted in an increase of daylight penetration deeper inside the space. [PERSON] and [PERSON] (2014) assessed the daylight performance of several interior light shelf configurations using side by side measurements of illuminance in two scale models which represent spaces 8.4 m long, 8.4 m wide and 2.7 m high in Johor, Malaysia (Latitude: 1.33\({}^{\circ}\) N) with a window-to-wall Ratio of 70.4% and glazing transmittances of 25%, 50%, and 75%. Single, double and triple light shelves made of aluminum (reflectance 51.29%) were evaluated with a depth of 0.3 m and 0.6 m (reflectance 51.29%) and variable cleststory heights (0.3 m and 0.45 m) under various sky conditions, as illustrated in Figure 4.0 The internal light shelves were able to improve uniformity by as much as 30-90% under intermediate sky without direct sunlight when compared with the base case (without light shelf). The results proved that internal light shelves were not only effective to reduce the extremely high illuminances at the area near to window, but were also able to increase illuminances at the deeper area of the room and this occurs even for overcast conditions. According to the findings, the most effective performance was achieved in low zenithal angles. These results are contradictory to the results presented by [PERSON] (2014) whose main findings suggested a reduction in illuminance levels under overcast sky conditions. [PERSON] and [PERSON] (2014) proposed a methodology for determining the best light shelf arrangement using the simulation of a typical office unit for six latitudes for three different office heights using CIE Standard overcast sky. Indoor illuminance values were correlated with various light shelf sizes and positions and as a result, a set of curves were created. These curves (CUN-OKAY) can be used to estimate a proper light shelf for a specific location. [PERSON] and [PERSON] (2014) used both illuminance measurements in scale rooms in Chennai, India (Latitude: 13.08\({}^{\circ}\) N) and simulations to test the impact of two types of light shelves (specular and diffuse) and their tilt angles on the daylight distribution. Measurements showed that when a horizontal light shelf (aluminum or mirror glass) was used, there was an increase of about 21% in illuminance levels. Surprisingly, the simulation studies showed that in 30% of the examined cases, the light shelves increased the illuminance near the window reducing illuminance uniformity. [PERSON] et al.