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Libraries University of Michigan Library

University library gets lighting boost from
fluorescent fixtures with prismatic design

Narrow aisles and high shelves make library stacks notoriously difficult to light well. In the Kresge Business Administration Library at the University of Michigan, Ann Arbor, student complaints about inability to read titles and call numbers on books in the shelves provided the impetus for a lighting retrofit of the 17,500 square-foot central stack area.

Fixtures chosen for the project are Percepta II luminaires from Holophane Corporation, selected because of their "bat-wing" photometrics. The fixtures' prismatic design produces a twin beam pattern that generates beneficial sideward illumination, which was necessary to light the eight-foot high shelves evenly from floor to top shelf.

A total of 132 fixtures with single T8 lamps were installed, replacing the same number of luminaires using two T12 lamps. The previous fixtures had a vertical design, with one lamp mounted on top of the other. A standard ballast was used.

Surface-mounted Percepta II luminaires are installed parallel to the shelves, versus the perpendicular placement of the previous system, which resulted in spotty illumination. Units are linked end to end, with one ballast operating two fixtures. Mounting height is 10 feet, with spacing at 4 1/2 feet.

The result of the retrofit has been a significant increase in light levels. Previous illumination levels in the stack area, which has an 11-foot ceiling, were three to five footcandles. Since the retrofit, levels have jumped to 16 to 20 footcandles. Illumination has increased not only in the stacks, but the carrels located along the side. With the new fixture configuration, luminaires are located directly above the carrels, providing more light for students to read and study.

Energy savings resulting from the retrofit were significant enough to earn the University a $3,684.50 rebate from Detroit Edison, based on a 80,295 kilowatt-hour savings per year. Payback for the project is five years.

While the University's original plans called for retrofitting half of the fourth floor, because of increased light levels, the decision was made to complete the entire floor. Presently, the University has no plans for regularly maintaining the luminaires; lamps and ballasts will be changed as needed.

Fixtures, controlled by a switch, are illuminated during library hours. Twenty fixtures remain lighted through the night. Yoshiko Hill, utilities engineer, Utilities Department, University of Michigan, served as project engineer.


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