Invigorating Philadelphia's City Hall with an Illumination Infusion
City Hall is one of the true treasures of Philadelphia. It sits at the very center of the city's grid of streets, as envisioned by William Penn when he laid out the city in 1681. Built over a period of more than 30 years at the end of the 19th century, it is now a registered National Historic Landmark, the finest example of French Second Empire architecture in the United States, and the tallest masonry bearing-wall building in the world. Square in plan with a center courtyard, this building has over a million square feet of interior space, making it the largest municipal building operating in this country. Its richly ornamented perimeter facades extend nearly 500' (152m) along each side of its Centre Square site, facing the city in all directions.
In 1999, the Capital Program Office (CPO) of the City of Philadelphia, with a team of architects and engineers led by Vitetta Group, began an ambitious project to restore the facades and roofing structures of City Hall. With this exterior envelope renovations project, Vitetta joined with lighting designers from The Lighting Practice and engineers from Vinokur-Pace to design a new facade lighting system for the building. CPO recognized that the existing lighting fell far short of achieving the kind of nighttime highlighting this distinguished building deserved.
This project, which is still in process, is a unique opportunity for lighting in the city. No other building in Philadelphia occupies as prominent a location. City Hall rises out of the intersection of Broad and Market Streets — the north-south and east-west axes of the city grid — and continues to dominate the views along those corridors. The Tower of City Hall has long been visible from the major highways surrounding the city and from the city's many neighborhoods. Moreover, in addition to the many carved stone and cast-iron ornaments on its facades, the building has over 250 pieces of fine sculpture designed by Alexander Milne Calder built into its architectural fabric, more sculpture than on any other building in the country. The lighting design team began with the belief that appropriate lighting could not only energize those many nighttime views of the building from a distance but also dramatically enliven City Hall's immediate surroundings.
Under the existing lighting scheme, the facades are generally left so dark that the Tower with its illuminated clock faces seems almost suspended in the air, disconnected from the building. The form and detail of the building are mostly lost in deep shadows. Only fragments of the facades are made visible, and those are overly bright. The mercury vapor lamps of the existing uplighting fixtures mounted on the facades produce stark greenish highlights and disorienting shadows, giving the building an incoherent and uninviting appearance.
The team resolved that the new lighting treatment should be as responsive as possible to the architectural character of the building, and compellingly render its sculptural forms without the distortions of unnatural shadows. The team noted three key features to respond to on the perimeter facades of City Hall.
These are articulated into a repeating pattern of distinctly different sections. The Center and Corner Pavilions are the tallest and most prominent sections of the building, and the Wing and Curtain sections between the Pavilions progressively recede. A lighting system that treated all of these sections uniformly would tend to work against the hierarchy inherent in the building design.
Within this architectural hierarchy, the facades of the Center and Corner Pavilions are the most dramatic and richly detailed. They incorporate a projected framework of freestanding columns and they have the most ornate sculptural decoration. Emphasizing the Pavilions in the new lighting scheme would not only echo the building's architectural hierarchy, but also provide variety and a better sense of scale within its overall nighttime image.
The profusion of stone carvings and sculpture incorporated in the facades, particularly at the Pavilions, offers a wonderful opportunity to bring out another level of perception and appreciation of the building. If these carvings and sculpture could be lit warmly and coherently enough, they could draw the viewer beyond the perception of the building's general mass and shapes into a closer enjoyment of the details of these facades, creating a fuller and more satisfying nighttime image.
Through sketches, photographic renderings, and mock-up tests, the team tested these concepts for the perimeter facades and concluded that the different sections of the building should be treated with differing intensities, colors, and complexities of lighting. The Pavilions would receive the brightest wash lighting, the greatest concentration of facade-mounted warm halogen lighting to highlight their carved stone ornamentation, and warm white spotlighting of their sculpture groupings. The Wing sections flanking the Center Pavilions would have a somewhat dimmer wash lighting along with halogen accent lighting on window surrounds. The Curtain sections, between the Wings and the Corner Pavilions, would receive a dimmer wash lighting only. This treatment would use lighting in a particularly effective way — to create a sympathetic and engaging rendering of the inherent architectural qualities.
The team determined that the wash lighting for the facades — as well as the spotlighting of the facade sculpture — should typically come from the rooftops of surrounding buildings, to most closely approximate, with downlighting, the kind of easily legible, feature-defining shadows created by sunlight.
TOWERING ILLUMINATION
Concerning City Hall's Tower, the team reviewed a number of historic photographs and other sources and found that the Tower had been lit in a variety of ways in the past. In some cases, very little lighting appeared on the Tower. In other cases strong uplight sources grazed the structure and created long, dark shadows; while this effect could be quite theatrical, creating a foreboding appearance like a ghostly castle, it did not integrate well into a rendering of the building as a whole. While not as theatrical, the existing Tower lighting was also creating heavy shadows and harsh overlighting.
After considering several alternatives, the design team decided to create a soft “moonlit” effect for the Tower, treating it as a continuous architectural form whose lighting would be in balance with the facade lighting below. A consistent wash of metal-halide illumination would define the mass and details of the Tower's masonry without overemphasizing any feature. The intensity of this wash lighting would fall off somewhat at the top of the Tower so that accent lighting on the dark bronze statue of William Penn at its pinnacle would read strongly enough. The design team determined that this appearance could best be achieved by lighting the Tower from the rooftops of surrounding buildings — from two opposing directions only, in order to preserve feature-defining shadows on all sides of the shaft.
Another important consideration at the Tower was whether to change the illumination of its four clock faces. This is provided by standard fluorescent fixtures spaced evenly on a metal framework covering the back of each clock face. While the clock face itself is a translucent white material, these fixtures are currently lamped with yellow fluorescent “bug-lights,” reportedly introduced in the 1960s to simulate the “yellowing” of an aged clock face. The design team concluded, after mocking-up different lamp colors, that the current yellow color was much too strong, and discordant both historically and within the color palette of the rest of the facade lighting for the building. The new lighting design will return the clock faces to a warm off-white, closer to their historic color.
The design team selected halogen as the light source for the facade-mounted fixtures, because it could bring out all the subtleties of color and form that are present in the carved stone. Of all electric light sources, a halogen lamp is most like sunlight in its ability to accurately render color. In addition, miniature halogen lamps can be used to create precise beams of light in a very small fixture. The team researched fixtures and found that a unique low-voltage halogen fixture in a narrow weatherproof housing — recently developed for historic stone facades at the Louvre museum in Paris — would be a good choice for the facade-mounted fixtures at City Hall.
Its small housing would fit into the limited mounting spaces available in many locations, and would also be unobtrusive when exposed to view. The quality and spread of its light were ideal for lighting the carved stone features at the Pavilion facades. Also, its extended lamp life would significantly reduce the maintenance burden for the City. The Louvre fixture uses an enhanced halogen/xenon lamp that has an average rated life of 20,000 hours, roughly equal to five years of use on the typical City Hall lighting schedule. The design team intends to run the fixtures at a reduced voltage to cut energy costs and extend lamp life even further; this will be accomplished with dimming controls.
The fixtures distributed over the facades will be grouped into dimming zones, which will be operated through a preset control system. This will allow the team to set the appropriate lighting intensity for each zone and create a balanced composition of lighting across each facade. It will also allow for the creation of different lighting ‘scenes’ for special occasions or times of day.
Currently, the construction documents for the City Hall facade lighting project are nearing completion. Installation of the first phase of the new lighting design, including the Tower and facades on the east, north, and west sides of the building, will be initiated later this year.
Alfred R. Borden, IALD, is president of The Lighting Practice Inc.; James Bryan, AIA, is manager of the historic restoration studio at Vitetta. They can be reached at [email protected] and [email protected], respectively.