Daylighting performance improvement of a light-shelf using diffused reflection

Abstract

A light-shelf is a highly efficient daylighting system about which a great deal of research has been performed. However, improvements to the daylighting performance of light-shelves have been limited, because light-shelves could introduce external natural light into the interior space through specular reflection, rather than into a specific region of the interior environment. In this study, to improve the performance of a light-shelf, a light-shelf using the principle of diffused reflection was proposed, and its validity was verified through performance verification. The conclusions of this study are as follows: (1) The optimal angles of a flat type light-shelf and a light-shelf using diffused reflection could vary depending on measurements taken in different seasons. (2) With the installation of the light-shelf using diffused reflection in the summer, the uniformity ratio of illuminance could be improved by 29.9%-34.3% with the external type and by 10.4%-13.7% with the internal type compared to the existing flat type light-shelf. (3) For the light-shelf using diffused reflection, the lighting energy could be reduced by 7.98%-13.3% in the case of the external type and by 1.8%-4.4% in the case of the internal type compared to the existing flat type light-shelf.

A Review of Light Shelf Designs for Daylit Environments

“…Under overcast conditions, uniformity is also improved but this is due to the reduction of illuminance levels in the area near the window. Another way to increase uniformity is to use an optically treated upper surface [47]. By using small mirrored surfaces oriented properly, uniformity can increase by 29.9-34.3% for the external light shelf and 10.4-13.7% for the internal, compared to the existing flat mirror-type light shelf.…”

“…Lee et al [47] compared the performance of two light shelves, one mirrored and one using diffused reflection as this was achieved by a combination of various shapes of crystal faces located on the flat upper surface of the light shelf. A South oriented room in Seoul, Korea (Latitude: 37.56 • ) with dimensions 4.9 × 6.6 × 2.5 m was used which had 32% Window-to-wall Ratio.…”

“…The increase of the latitude decreases this angle [47]. In [60] Lee et al using a light shelf that is 0.6 m wide with a tilt angle equal to 30 • upwards for buildings in Korea achieved savings for both lighting and cooling.…”

Development and Performance Evaluation of Light Shelves Using Width-Adjustable Reflectors

“…In Table 1, we review and summarize previous research on light shelves [8,[10][11][12][13][14][15][16][17][18][19][20][21][22]. Based on these studies, we chose the angle of the light shelf as the variable to be applied for the operation of a light shelf in response to the external environment.…”

“…For each lighting, we used LEDtype lighting that is capable of eight-stage dimming control. For the performance evaluation of this study, 10 illumination sensors were arranged ( Figure 4) to measure the Width adjustability Effectiveness of a perforated light shelf for energy saving [8] 2017 Fixed at a certain value Not considered Performance evaluation of light shelves [10] 2017 Fixed at a certain value Not considered Daylighting performance improvement of a light shelf using diffused reflection [11] 2017 Fixed at a certain value Not considered…”