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Vital Signs
Project: Daylighting in Three Libraries
(Overview) (Method) (Survey) (Mt. Airy) (Michigan) (Exeter) (Syllabus) (Michigan Intro) (Michigan
Model Study) (Michigan Survey) (Michigan Student Evaluation) The Michigan Law Library (1974), designed by Gunnar Birkerts, is an addition to a classic Collegiate Gothic Library and campus quadrangle. Initially proposed as an above-ground addition that would "close" the corner of the campus quadrangle, the design evolved into a below-ground scheme, in part to resolve a complex of aesthetic concerns of any design within the traditional campus and also to meet a restricted budget. Due to underground placement, the skylighting provides the only evident connection to the outdoors. The design accomplishes this through a generous atrium and skylight that includes vertical mirrors mounted on the inside of the major skylight mullions that serve as light reflectors much like a lighting fixture or illuminaire. Findings of the field visit to Michigan Law Library were surprising in that "so called" visual and lighting problems that had been anticipated by preliminary model testing-essentially, the initial hypothesis that sunlighting would be too bright under the skylight and that this would create an unacceptable contrast ratio between skylit and electrically lit areas-were not evidenced either by on-site evaluation or by user responses. Students using the library can select from desks placed under the skylight or in relatively private reading rooms. The survey included readers in both conditions, that is, at open daylit desks and in closed reading rooms with only electric lighting. Survey responses indicate a higher user satisfaction with lighting in daylit areas, compared to respondents using the electrically lit reading rooms.
Hypothesis prior to field testing The intention was to test the daylighting effectiveness of the below-ground design. When the students studied the lighting model, questions arose about how effective the skylighting might be in bringing the sense of out-of-doors into an underground building. Based upon the daylighting model tests in full sun conditions, it was "guessed" that the design had a problem with "overlighting." An hypothesis was thus formulated, that the daylighting was imbalanced, and the field test undertaken essentially to determine whether or not this was the case. On the other hand, the quality of lighting of the model studied under the artificial sky appeared to be very effective and pleasant due to the diffusing effect of the sloped wall which acts like a reverse lighting reflector. The model study also revealed an interesting and varied natural lighting design due to multiple reflections, although it was not known whether the model accurately replicated actual conditions. Measurement of the lighting model indicated very high daylight factors, with direct sun falling on the reading areas for part of the day. It was surmised that these areas would not be used during these overlit periods, a premise that based on the field visit proved to be entirely incorrect. Methods Two students teamed to make the original model and measurement (Kirsten Youngren and Genevieve Black), but only Genevieve was able to undertake the field test, which consisted of lighting measurement, interviews with the librarian, along with distributing and collecting the questionnaires. The evaluation was carried out during two periods on the same day, first in the morning when attendance was relatively low and then later in the afternoon. Sun conditions were changing during the day from early clouds to partly sunny. While many students chose desks directly under the skylight, a nearly equal number of students chose to locate in closed and electrically lit reading rooms, ostensibly for privacy and proximity to book stacks. This provided the opportunity to compare two contrasting conditions, daylight and electric lighting. Results and conclusions As noted, the operating hypothesis was proved incorrect. The daylighting in the library is extremely effective, with a high degree of light reflectance and diffusion that results from the unusual cross-section. The library is amply lit throughout, with an acceptable "contrast" between brightly daylit spaces and other spaces (stack areas with low level electric lighting) providing relief and variety. The fact that there are two wings, one with the skylight facing north and one facing east, creates a range of lighting conditions from sunny to shaded at any one time. One can choose to locate a study desk in a bright lit (sunlit) wing or go the a less sunny, but still brightly diffuse, area. The building's orientation and skylight reflectors serve to diffuse and reflect sunlight, making the atrium bright and pleasant under both sunny and cloudy conditions. While excellent daylighting quality is thus achieved, glare from the lighting fixtures and their seemingly haphazard placement (not aligned with the geometry of the atrium) indicates insufficient coordination between daylighting and electric lighting layout. This was the one critical design issue identified by field observation, (although a persisting leak at the rear skylight was evidenced by a makeshift drain and wastepaper basket!). Readers in this "underground" library preferred the bright sunny locations (at least during the Spring days that the occupant survey was undertaken...perhaps the library users were "sun starved!"). Survey responses indicate a higher favorability rating for the daylit areas, compared to the electric lighting in the reading rooms. This example turned out to be among the best of the daylighting designs that the class investigated and the only one (of three) where all survey respondents rated daylighting conditions as comfortable and more favorable than electrically lit reading areas. This conclusion provides a cautionary tale not to rely upon only upon interpretation of daylight model testing. . . field observation and measurement substantially changed the initial presumptions. The next section presents the results of daylight model testing for the University of Michigan Law Library. |
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author: vitalsigns@ All contents copyright (C) 1998. Vital Signs Project. All rights reserved. Created: 05/13/97 |
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The University of Michigan Law Library was designed by
Gunnar Birkerts. The building was completed in 1974.
