When it comes to thinking about lighting, two common misconceptions dominate library design. The first is that cutting energy consumption equals sustainability—it doesn’t. Then there’s the notion that everything in a library space should be equally lit, which in practice just means that lighting fails to draw attention to or emphasize any part of the space. Dashing these notions guided the lighting design during the renovation of Madison Public Library’s (MPL) Central Library, WI. The result is an architecturally integrated lighting system that helps to transform a decrepit 1965 building into a state-of-the-art facility, registered for Leadership in Energy & Environmental Design (LEED) Gold certification, with a highly flexible architectural interior and an operational lighting demand almost half of what is allowed by code.
The architectural design of the renovated Central Library addresses sustainability on many levels, most notably through the use of a raised-floor mechanical plenum, ultra-efficient mechanical systems, a photovoltaic (PV) array, and a green roof. Windows were expanded to let in more daylight, simultaneously cutting power consumption and lighting the space in a way that organically connects users to the time of day and the weather. Each lounge chair, study table, computer table, display kiosk, and book range/row of shelving is designed to be moved. Thus the library can be fully reconfigured to address ongoing shifts in library service, collection storage, and spaces for collaboration without undertaking another renovation. Meeting the energy targets and providing a healthy, high-quality library interior required developing a selective lighting system combined with automated lighting controls.
The wrong cuts won’t last
The health and well-being of building occupants depend on lighting that is visually comfortable for reading and navigating the space, as well as glare-free, color-corrected, visually interesting, and at an appropriate level as advised by organizations including the Illuminating Engineering Society of North America.
Designers and engineers must avoid reducing ambient light levels in an effort to lower energy use at the expense of light quality. Though this strategy may result in the minimum recommended light levels, a focus solely on light reduction will result in interior spaces that appear dark thanks to contrast between reading surfaces such as desks and walls. That perception of darkness can create the need for extra lighting down the road. It will also lead users to override daylight compensation controls, which reduce interior light levels based on the amount of daylight available. Once these changes are made, energy savings will be lost.
The renovated MPL Central Library avoids these problems by using a selective lighting system that addresses visual and psychological health as the primary goal and reduces light intensity where appropriate. The result is a 46 percent reduction in lighting energy demand relative to basic code requirements and an energy use reduction of an estimated 70 percent relative to the lighting originally installed in the 1965 building.
We have all benefited from studies, like Cornell’s groundbreaking 1988 report (bit.ly/1i8XtJ4), that document the importance of interior daylight in improved productivity and emotional wellness and from surveys illustrating that indirect light improves visual comfort. However, these reports do not address whether uniform lighting throughout a space is healthy, visually interesting, or conducive to energy-reduction strategies. Some other examinations suggest that uniform indirect lighting can affect people adversely and most indirect lighting strategies result in high energy consumption.
In general, buildings in the United States are overilluminated. Libraries, where it is most economical at the time of construction to provide one overall ambient lighting system, are no exception to this rule. Library lighting designs consistently incorporate direct/indirect lighting systems as an accepted method of creating visually comfortable and consistent spaces. Conventional wisdom states that a uniform lighting system will allow for more flexibility in the future because book ranges, study areas, and lounge seating can be moved anywhere anytime the library staff choose to do so. However, a single, consistently uniform, lighting system must provide sufficient illumination for the most intensive task: lighting stacks. That means the same lighting system will make study tables, computer tables, and lounge seating overly bright and users uncomfortable while increasing energy costs.
Light where you need it
By contrast, the lighting system in the Central Library is fully integrated into the flexible architectural design and optimizes task and surface lighting, with minimal ambient light. The selective lighting system was designed to craft a relaxed, visually interesting, and energy-efficient building that can be fully reconfigured without uniform light levels. Lighting was designed based on the visual requirements of specific functions (e.g., reading, browsing, using a computer), and the ambient light in each function zone was intensified to compensate for visual contrast. Overall ambient light is at an appropriate level of 15 footcandles, whereas walls and ceilings are illuminated to develop an impression of brightness, give form and clarity to very large rooms, and reduce contrast owing to daylight. The result is a system that enhances the spatial qualities of the interior and significantly reduces the lighting energy demand (see sidebar p. 9) while still providing flexibility in how spaces can be used.
“I was excited by the plan to feature up-lighting on the main levels and have been extremely pleased by the results,” says Mark Benno, MPL’s administrative services manager. “Not only does it soften the glare of traditional fluorescent lighting, but it accents one of the building’s strengths: the original waffle slab ceiling. The geometric pattern of the ceiling, combined with light reflecting off of its surface, produces a well-lit environment without harsh, direct light.”
Energy codes require lighting systems’ electrical demand to be calculated based on the worst-case condition, in which every luminaire that is hard-wired into the building is operating at 100 percent of its rated demand. Lighting power density (LPD) is not modified by reducing lamp wattage or installing controls. As a result, the real life energy savings of setups like Madison’s that use those tools will likely be even greater. The Central Library’s selective lighting system is designed to operate at a full electrical demand of 0.91 watts per square foot (sf), which is 30 percent below the energy allowed by the code in place at the time of design (2007 code, 1.3 watts/sf). But the lighting in study rooms, conference rooms, service rooms, offices, workrooms, storage rooms, restrooms, and kitchens and at computer and study tables is automatically switched off when not needed. Meanwhile, daylight sensors dim the interior electric lighting when sufficient daylight is available. These reductions in lighting use put the typical operational lighting demand at around 0.70 watts/sf, meaning that the library runs 46 percent below the energy code allowance and fully 70 percent below the installed lighting of the building before the renovation.
Light that moves with you
The renovation of the Central Branch prioritized increased flexibility, which created a need for mobile furniture, display kiosks, and stacks. A raised floor allows for an underfloor mechanical and electrical distribution system while also strengthening the selective lighting concept, by allowing lighting to be integrated into the furniture, stacks, and lounge seating layouts. Thus, lighting, cords, and plugs are as easy to move as tables, kiosks, seats, and stacks. Receptacles under the raised floor are color-coded to identify specific plug locations for automated building- controlled lighting and equipment, daylight-controlled lighting, and computers and equipment required to be fully on at all times.
The lighting mounted on the book stacks was specifically designed to break apart at 3′, 6′, or 12′ intervals, depending on the length of the shelving range. Sections can be removed incrementally as the size of print collections decreases over time. Electrical codes required the stack lighting to be hard-wired into the underfloor system, but the underfloor electrical boxes can easily be modified when book stacks are ultimately removed.
A hallmark of design excellence is visual variety. Successful lighting strategies respond to interior details. The Central Library’s unconventional lighting strategy reflects the atypical character of the library’s architecture. Visually interesting spaces include variety in scale, texture, color, and especially lighting. At MPL, the design team wished to play up the texture of the existing building’s concrete structure and to provide visual interest by creating a variety of light intensity/color/type conditions customized to each function, for instance, in lighting the local art on display. The Madison community has a rich and deep appreciation for the arts, and the design team honored that tradition through integrating art into the building wherever possible. While incandescent lighting has fallen into disfavor of late, it is still the best option for showcasing art. The lighting in the Central Library is primarily fluorescent, but low-voltage halogen lamps accent a historic restored mural and light the third floor gallery. Color-corrected low-voltage MR16 bulbs were specifically chosen for longevity and intensity and can be easily replaced with LED MR16 bulbs when technological advances make those less energy-intensive lights a satisfactory option.
Why not led?
In 2012, when the City of Madison signed the contracts for its library construction, LED (light-emitting diode) lighting for interior applications was still in its adolescence and not economically viable for the project. Color quality was inconsistent, unshielded luminaire designs offered disturbing glare in exchange for lumen output, and the amount of light delivered per watt consumed was less than the fluorescent lighting systems specified. However, with the newest developments, significantly better LED sources and luminaires are available today.
Designers must continually evaluate the changes in solid-state lighting systems and specify LED luminaires only when they appropriately contribute to the light quality of the space and cost objectives of the project.
In addition, the children’s area reading caves are illuminated via pressure-sensitive pads that trigger the lighting when a child climbs into the cave. A combination of LED and fluorescent strips is used inside the caves: LED for its very small size and sparkle and fluorescent to provide adequate light for reading.
This approach continues even outside the building: the library responded to public concern about the darkness of the adjacent streets “by opening up windows along the street, adding an LED light wall and lighted Madison Public Library sign,” Director Greg Mickells says. These served dual purposes, “providing a more welcoming, safer presence and also bringing more visibility to the activity occurring inside the library building. Combined with our lighted ‘Question Mark’ sculpture, lighting of the building’s exterior serves as an ongoing advertisement for the energy and creativity our visitors can expect to find inside.” The exterior lighting uses only 2500 kWh/year, equating to about $350/year.
The most notable lessons learned from the process of redesigning MPL’s Central Library emerged from integrating lighting into furniture, coordinating construction trade responsibilities, and managing the sequence of bidding. Furniture, fixtures, and equipment (FF&E) services are typically a separate contract from the architecture, negotiated after the bid for general construction. Lighting is part of the general construction, and electrical contractors are responsible for bidding, purchasing, installing, and energizing hard-wired luminaires. A process was required to allow each trade to bid, provide, and install their respective systems without voiding UL listings and warranties of either the furniture or the fixtures.
Making the MPL lighting scheme flexible and adaptable required close collaboration among the design team, furniture supplier, and lighting manufacturers. Because the table modifications were on a different bidding track from the lighting modifications, the sequence of engineering and specifying the luminaires for the general construction bid became a challenge. Ultimately, the table lights were taken out of the general construction bid and absorbed into the FF&E package. The luminaires were factory- modified as required for the table stands and fitted with cords and plugs. The furniture manufacturer then purchased them and installed the table stand, table attachment, and luminaire as part of a single table assembly.
Coordinating lighting installations on the book stacks required a considerable amount of building trade and design team coordination during construction. The lighting installation was designed with a channel attached to the top of the book range to conceal ballasts, junction boxes, electrical conduit, and fluorescent strips for up-lighting and to provide a solid location for attaching the mounting arms for the fixtures that would illuminate the collection. The channels were put into the book stack contract with the intent that they would be structurally attached to and become a seamless part of the completed book ranges for future flexibility, but the process was occasionally trying.
Lighting installation mock-ups and electrical inspections resulted in modifications to the channel, electrical wiring, up-light, and luminaire mounting arm. While the end product is one we’re proud of, the road to it could have been simplified and less costly had the channel been specified as part of a complete lighting assembly provided by lighting manufacturers, a lesson that shouldn’t be lost on libraries facing similar design decisions.
The coordination extended even to painting: the lighting strategy at the MPL relies heavily on high light reflectance throughout the interior, so white paint and bright surfaces are used wherever practical. In some areas, the light surfaces are at odds with the high use of the library, requiring increased attention to maintenance. Periodic repainting will be an important part of the library’s operations going forward.
To achieve this lighting strategy took about one-third more design and coordination time up-front as compared to a more conventional lighting approach, such as recessed direct/indirect lighting and a modest number of accent lights. It also cost more: the lighting itself cost approximately $11/sf in 2011 dollars, compared to a conventional lighting approach at $6–$7/sf. But in the long term, the 70 percent energy savings this will produce will recoup those up-front expenditures. For MPL, this equates to roughly $33,000 per year in savings. While energy costs and savings will vary with specific locations, it seems clear that taking a fresh look at library lighting can help save the pocketbook as well as the planet.