# A Review of Light Shelf Designs for Daylit Environments
## 4 Conclusions
using a light shelf that is 0.6 m wide with a tilt angle equal to 30\({}^{\circ}\) upwards for buildings in Korea achieved savings for both lighting and cooling. They suggest that during winter the light shelf should be removed to save energy. It seems that the equation (4) proposed by [PERSON] [50] give results compatible with those found by [PERSON]'s work [51] while diverging slightly from those of [PERSON] and [PERSON] [46]. * It seems that the shape of the ceiling can affect the distribution of illuminance. When chamfered ceiling is used, the illuminance levels increased in the rear part of the room by 21-36% and decreased by 20-55% in the front. If specular ceiling is used a further increase in illuminance levels occur [39; 52]. Changing ceiling surface reflectance type to specular further increased illuminance levels in the back of the room was observed. In addition, the external curved and chamfered exterior light shelves performed better when a curved ceiling is used [54]. * Dynamic control of mirrored light shelves can offer some benefits since they can redirect sunlight into a specific area on the ceiling. The results suggest that small window-to-floor ratio achieve the largest percentage increase in daylight illuminance in the deeper part of the space. Motorized designs achieved an increase in lighting energy savings in comparison with a static mirror light shelf from 8-22% [42; 51; 53; 62; 70]. As already mentioned, a light shelf is one of the simplest daylighting systems. Regardless of its ease of installation, it should be designed to suit specific demands, and this can pose a difficulty since it requires specific knowledge. Despite the research already made, there is little information on how light shelves can be best practically used. We believe that further research is needed with light shelves installed in real buildings where post-occupancy evaluations can be realized together with measurements. In a full-scale system, all possible inaccuracies of the reflective surface together with the deterioration of its reflective properties over time could be assessed. Of course, real scale testing is accurate but is also expensive and consequently simulation is used instead. This is a challenge that we need to address. The material used at a light shelf's upper surface must sustain a very high reflectance value over time. Metal mirrors are available today offering several advantages since they have the formability needed for curved light shelves together with excellent maintenance characteristics. Unfortunately, maintenance costs have not been investigated thoroughly with respect to daylighting systems literature [77]. Dirt can reduce 8-12% the reflectance of mirrors [78] and thus, a variety of coatings have been developed to improve mirror performance. For example, TiO\({}_{2}\) coatings are used today as anti-soiling layers. This approach is considered as a preventive technique while restorative techniques are used as well (i.e., manual cleaning). Despite the adoption of computer simulation programs, the complexity of these programs together with their limitations in simulating optically complex surfaces and/or actively controlled reflecting surfaces can be identified as weaknesses when it is required to estimate a system's performance on an hourly basis. The majority of building energy simulation tools use time series of work plane illuminance to estimate the energy savings due to the adoption of a daylight responsive lighting control system with known characteristics. This information is useful when various design alternatives are compared but it is of a limited value when a close to reality estimation of savings is required. The ceiling placed photo-sensor corresponds to incident illumination and converts it to a control signal. Selection of a sensor's proper field of view according to the geometrical characteristics of the space is quite crucial in optimizing the performance of the system.