There is a perception among some members of the design community that lighting of precast concrete parking structures is not as efficient as lighting of post-tensioned concrete (PT) parking structures. This perception occurs because one assumes that there is more light blockage from the closely spaced, precast concrete double-tee stems (5 ft [1.5 m] spacing) compared with the wider spacing of beams (18 ft to 24 ft [5.5 m to 7.3 m] spacing) in a PT concrete parking structure. The Colorado Prestressers Association retained Walker Parking Consultants to perform a study comparing lighting systems for precast concrete parking structures versus PT concrete parking structures. This study indicates that there is no difference (within the accuracy of the calculation procedure) in horizontal illuminance on the floor, or vertical illuminance on the perimeter walls, for identical lighting configurations in precast concrete and PT concrete parking structures. This conclusion requires that the bottom of each luminaire in the precast concrete parking structure is pendant-mounted and that the luminaires are no more than 6 in. (150 mm) above the bottom of the double-tee stem and centered between the 5 ft double-tee stem spacing (Fig. 1). This report describes the configuration of the two parking structures, the lighting configuration, the design methodology, and the results of the analysis.
