An Empirical Study and Analysis of Daylight Penetration Through a Light Plenum

Abstract

Lighting accounts for approximately 54% of the annual energy consumption of office buildings, and can effectively be reduced through daylighting. The simplest way to provide day lighting into a typical office space has been to use unilateral sidelighting. Discomfort and visibility glare from unilateral sidelighting cause the occupant to close drapes or blinds and turn on luminaries, resulting in an inefficient use of daylighting. One daylighting concept that has been developed to alleviate this problem is the light plenum. A light plenum can be added economically to an office space by using a hung ceiling simultaneously as a return air and light plenum. The appropriate opaque ceiling panels could be replaced with transparent ones to get the light to the rear of the space. The question is how much light can be expected to be transferred to the rear of the room and how different plenum opening configurations would affect those light levels. The result simply that a hung ceiling light plenum can provide adequate light to the rear of the room to balance the high brightness ratios created by unilateral sidelighting. Also, certain plenum opening configurations are more advantageous for certain sky conditions and orientations, and there are some which are of no benefit.