A passive core daylighting technology
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In this paper, we present the findings of a study that is currently evaluating the lighting performance of a horizontal hybrid solar light pipe that integrates daylight and electric light in deep floor plan multi-story deep buildings. The light pipe system was designed to deliver daylight at the back of a 10m space using an optimized geometry and high reflective materials. The light pipe was designed for latitude 30N in a predominantly sunny and clear sky location. An experimental testing room was built to represent a section of a south-facing open plan office space of 9.3m (30ft) long, 3.1m (20ft) wide, 3.6m (10ft) high, and an area of 29m2 (300ft2). Photometric measurements have shown that on clear and partly cloudy days (maximum external global horizontal illuminance, EXGH=110,000-120,000 lux), the light pipe can provide at the back of the space, 7.3m (24ft), between 300 to 2,500 lux for nine hours (9:00am-6:00pm). The highest illuminance values (over 1,000 lux) are achieved consistently between 10:00am and 4:30pm under clear sky conditions. Under overcast conditions the light pipe introduced more than 300 lux when EXHG was over 22,000 lux. Natural light is evenly distributed over the workplane, with a diversity of illuminance under 3:1 during most hours. Illuminance values at the back of the space, 5.4-7.3m (18- 24ft), are consistently higher (20-50%) than at 3.6m (12ft) from the window wall. Color temperature (CT) under the light pipe, 6m (20ft) ranged consistently between 4600- 5000K while outdoors CT ranged from 4700-5600K, under clear skies. The space showed a uniform daylight distribution, the sidelight window illuminates the front of the room and the light pipe system the back. Copyright (2011) by the American Solar Energy Society.
