Evaluation of a Deep Plan Office Space Daylit with an Optical Light Pipe and a Specular Light Shelf



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This research developed the Optical Light Pipe (OLP) as a feasible solution to solve the problem of insufficient daylighting in deep plan office spaces for predominantly sunny climates. It further combined the OLP with a Specular Light Shelf (SLS) to achieve uniform daylighting. This research was performed with an experimental setup of two 1:4 scale models of deep plan office spaces, modified from an earlier research on optical light pipe at College Station, TX. Blinds and shading devices were installed on the south fa?ade to provide daylight to the front zone of a 20 feet by 30 feet office module. The back zone was daylit by the OLP hidden in the plenum. The existing OLP design was optimized through computer aided ray-tracing. The SLS design was based on an earlier prototype designed at Lawrence Berkeley National Labs (LBNL). Results were based on observations made on clear and cloudy sky days between February 3rd and March 17th. The OLP achieved more than 300 lux of average workplane illuminance for 7.4 hours, when global horizontal illuminance was greater than 40,000 lux. It also achieved 200 lux of illuminance higher than an earlier prototype (Martins-Mogo, 2005) on workplane between 1000hrs and 1630hrs. It exhibited a glare free daylight distribution with luminance ratios well within prescribed limits on most of the vertical surfaces, with a relatively uniform illuminance distribution on back taskplane. OLP was better than windows with blinds and shading at providing diffuse daylight in backzone on a cloudy day, when global horizontal illuminance was greater than 20,000 lux. The OLP used in combination with SLS achieved more than 500 lux of average workplane illuminance for 6 hours, when global horizontal illuminance was greater than 40,000 lux. SLS also produced more uniform illuminance levels on the workplane at all times and on the leftwall at most times. However, it produced non-uniform luminance distribution on walls and ceiling and luminance ratios higher than allowable limits on the sidewall for some morning hours, and hence needed further refinement in design.