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Light and LibrariesLight and libraries Jeffrey Scherer The author Jeffrey Scherer is Architect and Partner, Meyer, Scherer & Rockcastle, Ltd, Minneapolis, Minnesota, USA <jeffrey@msrltd.com> Keywords Architecture, Libraries, Lighting Abstract Lighting - from the firmament and the filament- is intrinsically linked with library design, influencing many factors from user comfort and productivity to spatial perception and connotation. For centuries, daylight governed libraries, forging built form and determining access hours. Within the last 100 years, the ascendancy of electdc lighting has expanded possibilities and added challenges to library lighting design. The recent advent of the computer, and the light emanating from their screens, has provoked consideration of other light issues. This article addresses how to integrate light - in all its manifestations - within the context of library design. Ubra~/Hi Tech Volume 17. Number 4. 1999. pp. 358-371 © MCB University Press · ISSN 0737-8831 Introduction One speaks of the "light of reason" or "truth and light", associating light with the intellect and noble pursuits. In fact, Thomas Jefferson, who cried: "I cannot live without books", went further to comment that although tyrannies had often clouded "science and libraries", America sought to restore "light and liberty" to them. As Jefferson noted, light - in a metaphorical and literal sense - is a primary issue for libraries. Libraries are traditionally defined by daylight, not only as it reveals architectural form and provides reading light, but also in terms of how the sun historically determined access hours. Before electric or gas lighting, the dangers inherent in candles or oil lamps unduly exposed the library's valuable resources - its books and manuscripts - to fire risk. Many libraries, therefore, were only open during daylight hours. Although electric lighting allows extended operation hours today, natural lighting con- tinues to be a key factor in library design. It creates more productive environments and has other advantages, including visual appeal, true color rendition and cost (in contrast to elec- tricity, sunlight is free). Since we are heliotropic beings, lighting plays an important role in our sense of well being, mood and health. Modem electric lighting - sources offering their own advantages - of course, must be integrated into libraries, too, making lighting issues more diverse than ever. Computer screens, an addi- tional light source to be considered, means that in a short time frame, libraries have moved well beyond lighting concerns that traditionally dominated their design. Lighting is a main consideration in library design, influencing many factors from user comfort and productivity to perceptions and connotations of space. The purpose of this article is to "shed light" on this theme by helping librarians who are planning new or renovated libraries to work better with archi- tects and lighting engineers, in order to determine the most efficient and effective elements of a library lighting scheme. Our physical world is, after all, comprised of both natural and man-made elements. The interac- tion of natural and electric lighting will 358 Light and libraries Jeffrey Scherer Library Hi Tech Volume 17 ' Number 4. 1999 · 358-371 determine the efficacy of lighting the library and its contents. Light basics Light is a form of electromagnetic radiation and is the major medium through which we discover the world around us. As this radiation falls on objects, the brain, through the eye, discerns the size, shape, color, distance and movement of the object. Many factors affect the ability of the brain to recognize these physical properties: the angle and brightness of the light, the texture of the object, the speed of movement, the place- ment of the object in relationship to other objects, the contrast between objects and the source of the light. The power of light to influence perception, mood and even outward behavior of people is one of the most important aspects of designing with light. Nearly any light source, given adequate illumination level, can meet the purely functional criteria of seeing an object or viewing materials. It is this combination of perception and fact that makes lighting design one of the more elusive aspects of the library planning. The role of the individual designer's prefer- ences, the experiences and perceptions of the librarian or client representative and, finally, the impressions of the staff and patron all will influence the "success" of a particular lighting scheme. Before addressing strategies for successful lighting, however, it is necessary to understand basic, key factors about light and our perception of it. Introducing underlying issues is critical before delving into the issue of integrating natural and electric lighting and how the introduction of computer screens influences overall lighting themes. With this in mind, prime concepts to understand are the light spectrum, light measurement, reflectance and glare and brightness ratios: Light spectrum Light has many properties affecting human moods and ability to complete work or enjoy leisure time activities. Owing to the physical laws of electromagnetic radiation, only a small band of the spectrum is visible to the human eye. This band, commonly referred to as "ROYGBIV" for the red-orange-yellow-green- blue-indigo-violet range, has a nearly uniform spectral composition that produces white light. As a benchmark for white light, midday sunlight is generally considered to contain this full spectrum. Electric light, by its nature, can only approx- imate natural light, with different sources varying in their ability to mimic the full spectrum. The particular spectral composition of the lamp will establish its color rendering - one of the choices used in the selection of lighting types. The fuller the spectral range that a bulb produces, the better the color rendition becomes. For example, low-pressure sodium lights are virtually monochromatic, thus pro- ducing a yellow-orange cast. The color appearance of a lamp is expressed in terms of its color temperature. These temperatures are expressed as degrees Kelvin (K), with light source color varying directly with temperature. The higher the color temperature, therefore, the bluer (cooler) the light. Though counterintuitive, the more yellow (warmer) the light, the lower the color temperature. A bulb's color rendering is designated by the Interna- tional Commission on Illumination in its color- rendering index or CPI. Ratings range from 0 to 100, with 100 expressing the truer color rendition at its color temperature. One of the important lessons to remember in choosing the color spectrum of a lamp is that the broader the spectrum, the more energy the lamp uses. This relationship between the color spectrum of a lamp and the energy consump- tion (inversely proportional) should be remembered and used in making lamp choices. It will be a matter of judging energy costs against color rendition. Remember also that the appearance of any object wilt be determined by the light sources. Knowing that the color spectrum in the lamp will affect the color reflected from the object is of paramount importance in making the choice. The colors seen when viewing an object is the color reflected by that object. A white object reflects the total light spectrum. A black object reflects nothing- absorbing all of the light. A yellow object, for example, will reflect yellow 359 Light and libraries Jeffrey Scherer Library Hi Tech Volume 17. Number 4 · 1999 · 358-371 light and absorb the blue. For this reason, light source choice is as important as the selection of project finishes and fabrics. Logically, choices for a building's finishes must be made under the light planned for the space. This critical design consideration is very often misunderstood because of the common myth that an object has an intrinsic color. Based on these recommendations, lighting for general library tasks is set at 75fc. However, general area lighting is one-third of task light- ing, or 25fc. Non-critical circulation is a one- third of general area circulation, or 8fc (see Table II). Reflectance Table I Light measurement The amount of light emitted from a source is measured in lumens, analogous to the flow of water from a garden hose. Knowing lumen value, however, does not tell us how the emitted light is distributed. The initial luminous intensity is measured in candelas (cd) or candlepower, describing beam intensity in any direction. Luminous intensity, therefore, can be compared to garden hose pressure determining rate of flow. This measure is most important when designing with point source calculations. Lumens eventually reach and illuminate a surface. It is not possible, however, to compare light sources without some uniform method of measurement. Illumination is therefore used to indicate the number of lumens falling on one square foot of surface area. This unit of measure is called a foot-candle (fc) - the intensity of one candle flame on a square foot surface one foot away. The Illuminating En- gineering Society (IF, S) publishes light level recommendations, expressed as foot-candles, needed for a specific task, levels affected by many factors, including age (someone older generally needs more for a given task than someone younger) and task itself (one needs more light for reading than walking in a corridor) (see Table I). Recommended foot-candle levels for general lighting (fc) Public spaces with dark surroundings Simple orientation for short temporary visits Working spaces where visual tasks are occasionally performed Recommended foot-candle illumination on task (fc) High contrast, large scale work Medium contrast, medium intricacy Low contrast, intricate work over a prolonged period 3 8 15 We do not want to see the illumination, but rather the amount of light reflected. The brightness of what we see is, therefore, a function of both the illumination levels and the reflectance of the surface. Since brightness is the illumination reflected off a surface, it is also measured in lumens per square foot. The unit of brightness is given a different name, however, to emphasize that it is a measure of the light coming from an object and not the light going to the object. This measure is referred to as a footlambert, defined as follows: If one square foot surface is illuminated to 4 foot- candles and has a reflectance factor of 0.50, then the brightness would be 2 footlamberts. This factor is expressed as: Brightness divided by Illumination = Reflectance. Table HI lists some commonly experienced brightness levels expressed as footlamberts. Figure 1 shows the visual effect of different backgrounds on two triangles of equal shading Table II Task lighting Set to lES standards General area lighting One-third of task lighting Noncritical circulation One-third of general area lighting Table III Commonly experienced brightness levels (all units are expressd as footlamberts) Sidewalk on dark night 0.001 Sidewalk in moonlight 0.01 Sidewalk-dim streetlight 0.1 Book lit by candle 1 Wall in office 10 Well-illuminated table 100 Sidewalk - cloudy day 1,000 Fresh snow - sunny day 10,000 500W incandescent bulb 100,000 Poor vision Normal vision Normal outdoor brightness Blinding glare 30 Notes: Reflectance factors are expressed as a figure between 1 and 100 or 75 as a percentage: a white piece of paper is roughly 0.85; yellow brick is 150 0.35; dark stone is 0.05 360 Light and libraries Jeffrey Soberer Library Hi Tech Volume 17 · Number 4. 1999. 358-371 Figure 1 The visual effect of different backgrounds on two triangles of equal shading densities densities. It demonstrates the relative nature of reflectance, brightness and illumination. While it is the reflected light that we want to see, the manner in which it is reflected can affect our ability to use the light source to discern the shape, color or physical characteristics of the object or task. Reflections that are distractions include: · Reflected glare: or light that is reflected from a glossy surface to the center of our field of vision. This can be avoided by specifying flat or matte surfaces. The light source itself must be adjusted when the task has a glossy surface. · Veiling reflections: these occur from a bright light source on objects like a shiny maga- zine page. They are called veiling reflections because they reduce the ability to discern information on the printed page. These reflections are specular or mirror- like. For example, some ink or pencil surfaces can appear to disappear under the influence of veiling reflections. Eliminating veiling reflections is one of the major challenges of library lighting design. It is especially a factor with the multiplicity of video display terminals and the number of people reading materials, especially glossy reference materials. On the other hand, reflection is used to advantage in indirect lighting by bouncing light off a reflecting surface. to even out the contrast between the source and the surrounding surfaces, the muscles of the eye have to work harder and more frequently. Tired eyes and increased levels of stress result. Glare within the range that the eye can handle is discomfort glare; glare preventing us from doing a task is disability glare. In addition to these two glare categories, there is direct and indirect glare. Direct glare is caused when the eye looks directly into the source of illumination. Indirect glare results from light being reflected off surfaces. The relationship of the light source to the center of vision affects the seriousness of the glare. The closer a light source is to the field, the more serious the glare. In addition, the apparent brightness affects the glare. For example, a 100W bulb will have different effect in a room with dark surfaces than in one with light surfaces. Like the strain associated with glare, the eye has a difficult time adjusting to the brightness ratio between differently illuminated spaces within a building or between the interior and the exterior. Because brightness is a function of reflectance and illumination, the brightness ratio is controllable through good design. Anatomically, the eye is more sensitive to the brightness ratio at the center of the field of vision and less sensitive towards the periphery. By keeping the reflectance of wall surfaces within the following levels, excessive brightness ratios in general work areas of the library can be minimized (see Table IV). Table IV Recommended surface reflectance Minimum Area percentage Ceilings 70 Vertical surfaces 40 Table and work surfaces 50 Floors 20 Glare and brightness ratios The reflectance of a surface will affect the type of glare associated with that surface. Glare results when the source of the light is too great for the naked eye to handle. As the eye attempts Recommended brightness ratios Area Ratio Task to immediate surroundings 3:1 Task to general surroundings 5:1 Task to remote surroundings 10:1 Light source to large adjacent area 20:1 361 Example Book to desk Book to partition Book to remote wall Window to adjacent w Light and libraries Jeffrey $cherer Library Hi Tech Volume 17 · Number 4 · 1999 ' 358-371 These ratios should be used in the selection of furnishings, fabric, floor and wall coverings, and paint and wood for tables and millwork. These levels are recommended for areas where high visual performance is required, with the further recommendation that the task should always be slightly brighter than the surrounding. Light's ubiquity makes it easy to ignore its singularity and underlying concepts. With this section as a backdrop, however, it will be possible to discuss lighting issues as related to daylight, electric lighting, computer screens and library lighting strategies. Daylighting Library collections contain access to knowl- edge, yet are more than mere book warehouses. Traditionally, the best libraries provide users and citizens with innumerable oppornmities to explore the world around them, not only by reading the library's books, but also by using and experiencing the library itself. The library should manifest common values. The exterior should relay organizing principles of what "public life" entails; prime interior spaces should be a "meaningful microcosm", offering a reflective world view/order. A common thread found in noteworthy libraries is their use of daylight to reinforce the organizing concepts established by the mission of each particular library. Look to traditional reading rooms, the library's center, with tall, high windows reflecting the grandeur of the space. To enter this room, the best libraries evoke a keen sense of leaving the street realm and ascending to a book realm, accomplished through varied light levels and other architectural means. Passage and procession are harnessed to express the possibilities of learning, knowledge and attain- ment. Beyond this, the rooms observe the common rule that light will penetrate approxi- mately 2.5 times the window height. Thus, a large volume with high windows overall pro- vides overall good illumination. Light becomes an integral element of the traditional reading room, for practical use as well as for its symbolic, metaphorical allusions. Daylighting affords great design opportunities for all libraries, no matter what size. While this has been a given example for centuries, cheap and abundant energy has led to diminished emphasis on integrating daylight and architec- ture. This trend is being reversed as the psychological, physiological and economic ad- vantages of natural light are rediscovered. And given that daylight is a free, plentiful, renewable resource at most sites, it should receive prime consideration. With electric lighting commonly accounting for approximately 50 per cent of a library's energy budget, the use of effective daylighting to reduce energy expenditures has become a viable economic alternative. As outlined in the previous section, fewer than 100fc are needed for the vast majority of library tasks. Since the sun provides over 1,000fc even during overcast sky conditions, the issue is not availability, but rather controlling light. Under clear sky conditions, in fact, some regions have such abundant daylight that exploiting it is like attempting to drink from a fire hose. In arid, desert regions, the challenge is to allow light to enter a building without undesired glare or heat gain. The best archi- tectural designs respond to such circumstances with solutions specific to the region. Along with these regional considerations, other daylight factors such as the sun's different postures as its sweeps across the sky, natural weather patterns and seasonal concerns, com- pel and challenge design. In fact, daylight's possibilities and opportunities make it a prime generator of architectural form. The history of architecture can be traced through windows and the architectural means to control and shape light. Islamic latticework shielding occu- pants from the desert sun, Gothic expanses of stained glass, Japanese shoji screens filtering and diffusing light, and other examples of architec- tural innovation convey daylight's defining, elemental influence on architecture. Yet beyond formal, aesthetic concerns, the assets of daylight are reflected in law and legislation through history. From first century AD until the fall of Rome, laws established solar access rights. A British law, dating from 1189 and embodied in an 1832 statute, provides that if a window enjoyed uninterrupted access to daylight for a 20-year period, that right became permanent. Solar access prompted planning principles, that once adopted in 1905, affected Boston's urban fabric. In 1916, zoning 362 Light and libraries Jeffrey Scherer Library Hi Tech Volume 17, Number 4. 1999 · 358-371 ordinances were passed in New York that required skyscrapers to be built with setbacks in order to alleviate oppressive street trenches and facilitate sun penetration. In Japan today, building codes dictate that apartments receive four hours of direct sunlight per day. Innumerable aesthetic and legislative exam- ples reveal the importance of daylighting. Architects can effectively harness daylighting as a powerful resource by being mindful of its principles throughout the design process: · The sun's course across the sky is deter- mined by latitude. Site conditions, such as surrounding buildings and vegetation, may also influence solar access for all or part of the year. In a dense urban site, a neigh- boring building's reflective glazing might give unwanted glare. Understanding how to balance these factors will positively affect how the library is organized, as well as the distribution of window openings and shad- ing devices. · Consider your local conditions, the mix of overcast or direct sunlight, and other climate conditions. Architectural solutions will derive from these variations. For instance, overcast skies are evenly lit (entering sunlight bounces off clouds to produce a diffuse light) so the glare from direct light is not a pr/me issue. In areas where overcast conditions do not predo~ minate (such as desert regions), direct light may be a prime concern. · Recognize the solar arc. The sun is high at midday and easy to control with minimal overhangs. The rising and setting to the east and west is at low angles and difficult to control. Track these issues against space use. When harnessing daylight, ensure proper control within critical task areas to eliminate glare and unwanted heat gain. · Good regional architecture and vernacular solutions often offer insights. Courtyards in the southwest introduce tempered light in a building's interior. Conversely, traditional, small exterior openings reject light and its heat. In more temperate climates, narrow buildings with an east-west axis offer southern orientation, where south glazing can allow light to be controlled and the difficulties of Iow east and west sun angles can be minimized. · Orient spaces in the library to take advan- tage of natural light. If a meeting room is to be used primarily at night, then daylight may be relatively unimportant. Reading tables, rather than stacks, should be placed adjacent to windows to take advantage of the daylight, with stacks perpendicular to windows to facilitate light penetration (see Plate 1). · Recognize that lighting does not stop at the building envelope. Vines, trees and trellis can give seasonal shading, arresting the hot summer heat but also allowing winter sun to penetrate. Make sure daylighting strate- gies are reviewed for such seasonal variation. Reflecting pools or snow cover can also be used to introduce reflected light into a library. Or consider how light- colored walks or roofs may by used to reflect light inside (see Plates 1 and 2). · Lighting balance is important, with sources from two room sides more desirable than from just one. Clerestories and toplighting may be used in deep plan buildings. Direct beam lighting, interior and exterior light shelves and prismatic glazing also introduce daylight deeper into the space. It is also possible to differentiate between windows that provide light and those that provide view or ventilation (see Plates 3-5). · Light colored surfaces offer better distri- bution, maximizing the light that does enter. Similarly, splaying surfacing adjacent to windows reduces the gradient between Plate 1 Austin Public Library, Austin, Minnesota, Meyer, Scherer and Rockcastle, Ltd, Layering of spaces - reading tables near light, with stacks further off, :i:¢(,5.~.~¢:.: .............. . :: ~.~'"'::: .. Note :-...:.:.;.:.:.: :::::::::5::::: :~:::::::::::::: ~ ~::~:~:~::i that the stacks are perpendicular to the windows iiii!ii!iiiiil ...................... ........................ ::::::::::::::::::::::::: :::¢:::.:.:~.'::.:.:.:.:.:.:.:~::.:.'.' · '.:q.:.:.;.:-:.:.:.:.:...:%,:~ ~.~:.:...:...v.v...-.......-..:...: 363 Light and libraries Jeffrey Scherer Plate 2 Sahara West Public Library and Fine Arts Museum, Las Vegas, Nevada, Meyer, Scherer and Rockcastle, Ltd with Tate and Snyder Architects. Shading devices for library windows ,;. ~,: 4.:,,. · , ::~,~:::.; ,'::,-,,:.-.:.*,::., :~ ,..~ ;~;:,,:,~j:-:.q : .',,:..,...:,:,;,. .:::::s'.:::. ~ · :: ?.j.~.:..'~.~ :::.-..[5.~.S..~::?~4..: =========================== ;~;,~ . _" ~-_'-, r~r , :~f.<..':[:~ ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: · ':'* ' ~"~ "~ ~- ¢'"'"":'""'°'"';'":'"'"'~'"'">'"'"~i'"""'"'"" ~~,~,~: - ............ ~.;.-..~.=.=..-..-.....?..?.~:~: .~.~o .................... ;5;52.... 22:2:... 2: 2: , ?~ ......... ~,,~ ..................... ~,~~- ~ .. Plate 3 Sahara West Public Library and Fine Arts Museum, Las Vegas, Nevada, Meyer, Scherer and Rockcastle, Ltd with Tate and Snyder Architects the bright source, the window, and its immediate surroundings. Recognize the advantages of reducing the contrast between light sources and other surfaces (see Plate 6). Consider locating glazing as high as possi- ble to facilitate light penetration. Beyond this, computer programs, such as Light- scape and Lumen Micro, can quantify the performance of daylighting strategies within a proposed space. At the same time, they are able to produce qualitative rendering of the space (see Plates 7 and 8). Fluctuating energy prices should also be addressed. Initially and at current energy prices, it may be more cost-effective to ignore strategies like toplighfing. On the Library Hi Tech Volume 17 · Number 4 · 1999 · 358-371 Plate 4 Pleasant Hill Public Library, Hastings, Minnesota, Meyer, Scherer and Rockcastle, Ltd. Note the variety of light sources, toplighting from skylights and sidelighting from windows, to provide lighting balance 364 other hand, if effective toplighting can reduce the number of light fixtures needed as well as energy costs, it might be appropriate. High spaces facilitate day- lighting, countered by the cost of constructing a larger volume. Balance the long term against the first dollar (see Plate 9). A building "owner's manual", outlining cleaning schedules and maintenance con- cerns should be developed and employed. For instance, windows or reflecting surface that are covered with grime are not effective. Design intentions must be fol- lowed through after building occupancy, not surrendered owing to neglect. Daylighting affects building form. Optimal lighting might suggest building orientation in one direction, while urban or landscape features might suggest the opposite. Bal- ancing and juggling different, competing concerns is often necessary, and it is a factor that contributes to architectural richness. Light and libraries Jeffrey Scherer Library Hi Tech Volume 17. Number 4. 1999. 358-371 Plate 5 Sahara West Public Library and Fine Arts Museum, Las Vegas, Nevada, Meyer, Scherer and Rockcastle, Ltd with Tate and Snyder Architects, Natural lighting from two sides, stacks perpendicular to windows, high ceiling and windows and lights colors all facilitate good daylighting Plate 6 Merriam Park Library, St Paul, Minnesota, Meyer, Scherer and Rockcastle, Ltd, Toplighting to define library heart, with light colors surfaces to better distribute light = ===================================== ~ ::::::::::::::::::::::::::::::::::; ::::::::::::::::::::::::::::::::::::: ::::::::::::::::::::::::::::::::::::::::::::::; ::::::::::: ' ' x" :::::::::::::::::::::::::: ~! !: ~ !~ ~'.. :::: ........ In the context of library design, daylighting is an elemental, motivating issue. Weighing how daylight will enter your library is basic, yet it can be a complex concern. Ignoring its variability and delight, however, is not prudent in an age when environmental and regional considera- tions are increasingly predominant. Electric lighting In many lighting design proiects, the location and nature of the task is indiscernible. In library Plate 7 Sahara West Public Library and Fine Arts Museum, Las Vegas, Nevada, Meyer, Scherer and Rockcastle, Ltd with Tate and Snyder Architects, Toplighting from skylights penetrates several floors, Light- colored surfaces increase lighting effectiveness design, however, the tasks are varied and widely dispersed. Individuals may read at a table, scan reference materials at a stand-up counter, read a book in the stacks, search for a title, scan the stock market tables in a lounge chair, or read to children on the floor of the children's room. In concert and coniunction with daylight, electric light must be integrated to address this variety. From library use patterns, one might assume that the entire space should be designed to 75fc. This conclusion, however, would be particu- larly wasteful from an energy standpoint. It also ignores the design complexity of distributing light on vertical and horizontal surfaces, and prevents the control of its interference on computer screens. Light physics tells us that the amount of light from a uniform linear source (like a fluorescent tube) is inversely propor- tional to the distance, while light from a point source (like a spot light) is inversely propor- tional to the square of the distance. Thus with a Light and libraries Jeffrey Scherer Library Hi Tech Volume 17 · Number 4 · 1999 · 358-371 Plate 8 Carthage College Library, Kenosha, Wisconsin, Meyer, Scherer and Plate 9 Carthage College Library, Kenosha, Wisconsin, Meyer, Scherer and Rockcastle, Ltd. Daylighting and a variety of light sources. Image created Rockcastle, Ltd with Lightscapes ~..~g...**, ~ ......:,,;~.~ .............. , ~ ..:(~:~*-' ~ "~ . ~ - __~,~ ..... ============================================= ", B ~.~: _ "--, ~ "~*' '~ ....... ;:::~:~ :::::::::::::::::::::::::::::::::::: :.-5:-:'":::" -'. :: ::~¢~?¥}~;~;~?:;:;:¥:?,'-'"'~ .:.:+:+:.:.:.:,:.:.:.:.:.:.:.:.:+:.:.:.:.:.:.:.:.:.:.:.:.:+:...... · :::::: :..-.:.-~-,~.,--~-- ~. ~ ' ~ ~. [~?:~?:~;?:~??~?:~~:~,.*~:~:~:~:~¢~:;:~:~::;::~¢~~..~;~?.;.:~;::.:.~~ * lumens at ~e floor equals linens/ linear source, light available on a book spine four feet from the source is halved when the book is eight feet away. For this reason, the amount of light needed to reach the lowest stack shelf will be the determining design criteria. It follows that the closer the fixture can be placed to the top shelf, the fewer lumens that will be needed to light the book spines from the top to bottom. In short, mathematical equations and calculations, and the cost of paying for electricity, determine the amount of light reaching a task. To illustrate this concept, three examples are shown below. Each example illustrates a different lamping configuration but with the following common characteristics: · space between 84in. high stacks that are 3fl 6in. x9ft (i.e. three 36in. shelving units) with one fluorescent fixture; · ceiling height is 1 Oft; · fixtures hold 8ft-long fluorescent tubes; · fluorescent tubes are 38W each (75 lumens per watt); and · area on the floor served by light fixtures is 28fl2. Example A. Four lamps in one fixture: · one (four-lamp) fixture with 38W tubes ceiling height: 11,400/10 = 1,140 lumens; and · foot-candles equals lumens/area: 1,140/28ft2= 40fc. Example B. Doubling number of fixtures: · two (four-lamp) fixtures with 38W tubes equals 304W; · 75 lumens per Watt x 304W = 22,800 lumens; · lumens at the floor equals lumens/ ceiling height: 22,800/10 = 2,280 lumens; and · foot-candles equals lumens/area: 2,280/28ft2 = 81fc. Example C. Effect of lowering fixture height from lOft to 7ft 6in.: · One (four-lamp) fixture with 38W tubes equals 152W; · 75 lumens per Watt x 152W = 11,400 lumens; · lumens at the floor equals lumens/ ceiling height: 11,400/7.5 = 1,520 lumens; and · foot-candles equals lumens/area: 1,520/28ft2 = 54fc. equals 152W; 75 lumens per Watt x 152W = 11,400 lumens; These simplified examples do not account for ballast rating, power factors, lamp output depreciation, lens type, reflectance factors, contribution of daylighting schemes, fixture cleanliness, effective use of lighting controls, etc. They also do not account for a larger area of calculation. They do, however, show the Light and libraries Jeffrey Scherer Library Hi Tech Volume 17. Number 4, 1999. 358-371 relationship between distance and lumens. As can be seen, lowering the fixture to the top of the stacks (at 7ft 6in.) can increase the number of foot-candles by 35 per cent without changing the operating cost. While the simple cost per square foot for this area would be $0.81 for A and C, and $1.62 for B, the actual cost would be lower, when averaged over the entire building. The key objective is to gain usable foot-candles for the same operating cost. When thinking about library lighting, be careful not to take the easy path and assume that all spaces should be uniformly lit to a high foot-candle standard. In the illustration above, a small branch library with a public service floor of 6,000ft2 would have an annual energy cost of $3,800 (6,000ft2/36ft2 × $22.80) for the 40fc scheme and $7,600 for the 80fc scheme (based on average US energy rates). Use a strategy that enables the spaces to be lit for their purpose, yet one that is flexible if use changes. For example, the lighting scheme at the Brookdale-Hennepin Library in Brooklyn Park, Minnesota, has adjustable fixtures which can slide to new locations without the need to rewire or relocate the primary fixtures. Other factors to consider in developing a lighting strategy include: · Increase wall reflectance, within contrast ratios, and avoid large brightness ratios. In general, prov/de light colored surfaces with a combination of lighting types, both general indirect lighting and direct lighting. Reduce glare by correctly choosing and placing £~rtures (see Plates 10 and 11). . Provide only recommended levels of illu- mination. Use lower levels when tasks are not required. Place luminaries where needed. Do not place luminaries indiscri- minately; assess locations carefully. Use tasks, safety and overall aesthetics as balanced guidelines. · When possible, group tasks requiring the same standards of illumination. Consider reducing fixtures and ambient light levels by prowiding task lighting at tables (see Plate 12). Use photosensors and dimming systems linked to the amount of daylight available (see Plate 13). · Coordinate switching with tasks. Do not allow switching to be designed for "opera- tional simplicity" such as all-on or all-off. Plate 10 Pleasant Hill Public Library, Hastings, Minnesota, Meyer, Scherer and Rockcastle, Ltd, Toplighting and electric uplighting to define library spine Use occupancy sensors whenever possible, such as study and conference rooms and restrooms, to light only when occupied. · Use time clocks to control lighting. Turn off fluorescent fixtures if the space is vacant for more than five minutes, and turn off high-intensity discharge lamps if the space is vacant for more that 30 minutes. · Try to reshelf and clean during regular hours. If this is not possible, train staff on proper switching. Do not allow the staff to simply turn on all lights for convenience. Better, ensure that lights are switched to enable cleaning and reshelving to take place in stages. · Zone the lighting so that staff areas can be accessed during non-public hours. Con- centrate night parking in one area if possible. Zone parking lot lighting for security and needed spaces by activity. · Compare all lamp alternatives, using lower wattage lamps whenever possible. Evaluate lamps based on efficiency (lumens per 367 Light and libraries Jeffrey Scherer Plate 11 Merriam Park Library, St Paul, Minnesota, Meyer, Scherer and Rockcastle, Ltd. A mix of electric light sources gives balance .: ..... . .......... .::.. ;-: ......... ~ ¢%,~.~ ~,~ .....................-.. - · · ' ~-:---..:-'~.~.~~~========================== '-'.'.":.:-:-: ::: ~:~:: :J:J~: ::::::::L~;~'.~' '" ~' .......... ~ '...~ ......................... , . .'::--!:::'. ::... ...... . :.:'::" .:- .............. ~" ..~"' ~ ,~' ,.~. ~ ...... ~, , ~, ~ ....... ~ .... , watt), lamp color, color rendering, instal- lation and operating cost comparisons. Evaluate replacing existing lamps with lower wattage alternatives. · Eliminate incandescent fixtures. A compact fluorescent bulb uses 75 per cent less energy than an incandescent bulb, which is energy inefficient at giving tight while simultaneously increasing cooling costs. Evaluate heat removal luminaries to reduce cooling costs. · Complete a library energy audit. If new construction, gather costs on comparable libraries. With electric deregulation and rates in flux, it pays to be proactive. · Clean luminaries and replace lamps on a regular schedule. Replace outdated lumin- aries with the most efficient systems. Use the most energy-efficient ballasts available. Many factors will influence lighting energy consumption. Besides intelligent design and careful programming, individual efforts can make a substantial difference. Educate the Library I-Ii Tech Volume 17 ' Number 4 · 1999 · 358-371 Plate 12 Austin Public Library, Austin, Minnesota, Meyer, Scherer and Rockcastle, Ltd. Reading tables near windows, supplemented by task lighting Plate 13 Merriam Park Library, St Paul, Minnesota, Meyer, Scherer and Rockcastle, Ltd. A variety of daylight sources, from windows and skylights, and electric light sources provide for a good library environment patrons and staff to be energy conscious. Recognize that lighting will typically be 50 per cent of your energy operating costs. This cost could run as high as $10,000 per year for a 20,000fl2 library. Computer screens and lighting With the advent of the computer, library lighting has become a more complicated pro- position. Reading light emitted from a VDT and seeing the image on paper with reflected 358 Li§ht and libraries Jeffrey Scherer Library Hi Tech Volume 17 ' Number 4 ' 1999,358-371 light establish conflicting light requirements. Generally, when people work regularly with a CRT they are faced with several different visual tasks. Their eyes can move from the screen, to the background and to adjacent work tasks. Each time the eye moves, it attempts to adjust tO the new lighting level. If the degree of adaptation between visual tasks is too great, eye strain and fatigue result - a real problem for long-term tasks, such as for staff and patrons at reference stations. The most important consideration, in our opinion, is not the final illumination levels, but rather the difference between illumination levels. For this reason, we have cited the recommended maximum brightness ratios above. As the library becomes more reliant on information contained "on-screen", it is critical to understand the roles played by uniformity in comfort levels and by efficiency in use of lighting levels. Of equal importance is the issue of light f'm~cure reflections on screens. If the luminaire is a "bright source", it can create an uncomfortable field of view for the user, perhaps encouraging the user to "adjust" the brightness of the screen to compensate. This phenomenon is typical - one reason display tubes are lasting only two to two-and-one-half years at some libraries. Indirect lighting creates uniformity, enabling the user to appropriately balance the ratio between background and screen. Alternatively, deep-cell parabolic fixtures can create a dark appearance when viewed across the library space, thus creating a common dark field to a CRT screen. We recommend, however, that indirect lighting be considered seriously. This recommendation must be considered in the context of the ceiling height, energy manage- ment and practical limitations. A minimum ceiling height of 1 Oft is needed for this to work properly. Brightness should be controlled within a 60° to 90° zone in order to achieve visual comfort. A person will be looking typically at an angle between 60° and 90° from vertical; therefore, in this zone the control of the surface brightness of a fmture lens or louver will provide good comfort because of the uniformity (basis for visual comfort probability or VCP). Visual adaptation is another of the computer user's problems. 'We know that glare is annoying, yet it is not the cause of "eye strain". Instead, strain occurs when the pupil of the eye (the iris) dilates and contracts as it passes from a bright field to a dark one. Moving often from a reference piece of paper to the screen causes the eye to tire (visual fatigue). For this reason, the Illuminating Engineering Society (IES) has recently recom- mended lowering the foot-candle levels at the desktop. The basic goal is to have the CRT screen and the desktop task have similar brightness levels. Unless the distribution of the light out of the fixture is very broad, the uniformity of lighting levels throughout the space will be poor. For example, a person immediately below a fixture may find the space to be bright while a person between the fmmres may think it is too dark. The parameter that describes the broadness of the lighting distri- bution from a fixture is its spacing-to-mounting height ratio. Examples are: · prismatic lenses - 1.3 to 1.0; and · true deep-cell parabolic fixtures, which can approach 2.0 to 1.0. We are trying to achieve two contradictory goals: avoid brightness at high angles of view and, at the same time, spread out the light far enough from the fixture to get a large spacing- to-mounting height ratio. To lower the levels, the number of fixtures is reduced. The lower the number of fixtures, the greater the spacing, thereby causing problems with mounting ratios. Accomplishing this task with parabolic fixtures is, therefore, more difficult than with indirect lighting. See Appendix 1 for a checklist for planning your illumination strategy and Appendix 2 for more information about lighting levels for particular tasks. Conclusion In the past 100 years, library lighting has evolved rapidly, from a dependence on natural light to the integration of electric lighting. The emergence of computer screens in the past three decades has also greatly impacted lighting issues. Balancing these different light sources can be a complicated proposition, yet becomes manageable when daylight and electric light are 369 Light and libraries Jeffrey Soberer Library Hi Tech Volume 17 · Number 4 · 1999 · 358-371 envisioned as a building system that works in concert together. From site selection and programming to fixture, finish and equipment selection, as well as maintenance and upkeep, all involved must be mindful of the library's usage and how varying tasks - from computer screen use and Web surfing to reading and stack browsing - are addressed by the lighting system. Given the psychological, economic, health and other benefits of a well-conceived lighting strategy, the value of architects and engineers who understand lighting issues should not be underestimated. On the other hand, personal experience matters. We all use light, with personal preferences, tastes and an ability to judge what does and does not work well, a background allowing librarians to challenge and question design proposals. Beyond this, com- puter programs which provide accurate reflectance and light pattern rendering, or mock-ups of space, with actual lamps and product finishes, allow us to appreciate and better envision the end result. With these and other design tools, lighting design strategies and goals are becoming better defined. Vision is our most developed sense, light the medium for sensing our world. It naturally follows that light is a prime generator of architectural form. Envisioning how any build- ing will meet the sky through daylighting or be illuminated by electricity is a key consideration in renovation or new construction, but espe- cially in the case of libraries. We typically imagine someone reading under the shade of a tree under a blue, clear sky or by a glowing, yellow firelight. Though technology has evolved beyond this, computers themselves giving off illumination, light is still a defining library element, for the prosaic and practical as well as the profound. Appendix 1. Checklist for plan review (1) Make sure that the engineer or architect explains the overall illumination strategy. This plan should include lighting levels for each area of the library. If something is not understood, ask. Ask specifically for quan- tity, variety and location of lamping types. Scrutinize any non-utilitarian lighting carefully. Carefully consider future expan- sion plans and allow for the flexibility to 3?0 change lighting in case this becomes necessary. (2) Review the electrical plan with a transparent copy of the furniture plan overlaid. Check for placement of fixtures in relationship to video display terminals, book stacks, read- ing areas, staffwork areas and special areas. Coordinate number and location of outlets with equipment needs and the location of lighting in relation to tasks. (3) Request a copy of the energy calculations. Calculate projected operating costs as com- pared to library's annual budget for energy. (4) Make sure that the building program care- fully spells out: · Hours of operation that differentiate staff hours and public hours. This examination should occur on an annual basis. Timing controls can be set for seasonal changes in hours of operation. · Height of furniture and book stacks. Include the interior designer, ff prac- tical, in all decisions concerning lighting placement, wall type (reflec- tance and color), outlet locations, controls and equipment. Interior de- sign involvement will help to ensure that furniture and lighting are inte- grated and that conflicts are minimized. (5) Consider the method and location of light switching systems. Locate for ease of operation of timers. (6) Consider the number and type of lumin- aries and bulbs, as well as their maintenance ease for cleaning and lamp replacement. Minimize the number of varieties. (7) Make sure that the engineer or architect explains the security lighting. Analyze exit- ing patterns and how staff will close-up the library at the end of the day. Light accord- ingly so that no one has to exit in the dark. (8) Be aware of ADA compliance: · A clear approach to controls translates to a forward approach 30in. wide and 48in. deep, and a parallel approach 48in. wide and 30in. deep. · Maximum height of light switches from the floor should be 48in. Minimum distance from wall-mounted outlets to floor should be 15in. Light and libraries Jeffrey 5cherer Library Hi Tech Volume 17 ' Number 4 · 1999 · 358-371 Appendix 2 Table Al Lighting levels by task Area Reference stacks 6eneral collection stacks Note: a minimum of 10 fc on the lowest shelf is required Adult general reading areas: - tables with task lighting - task at reading table Note: we recommend ambient lighting for all reading and computer areas Long-term study reading areas Circulation desk Staff service points Staff service points (VDT tasks) Computer work stations Staff work stations Exception: when major staff tasks are related to computer, this should drop to 30 ESi with user-controlled task lighting lTV rooms (with note taking) Note: three-gun video projection requires black-out of room. Luminaires should be high, cut-off, parabolic type Audio listening stations Viewing stations - Microfiche Side table for reference Note: side table levels could be accomplished by use of task light Auditoriums Group study rooms Individual study rooms Note: include task lighting controllable by patron Note: a minimum of 30fo at desk height and a maximum of 50fc is recommended Corridors (between enclosed rooms) Corridors (between open areas) Stairways Restrooms Staff work room - repair area Map viewing Note: supplemental task lighting recommended for areas such as map viewing Lobby spaces Elevators Notes: Foot-candles are on the horizontal or vertical surface ESI is the Equivalent Spherical Illumination for the volume of space Measured level Horizontally at 42in. Vertically on bottom shelf (12in,) Within space at the task Horizontally at 36in, Within space at the task Within space at the task Within space at the task Illumination on screen Within space at the task Within space at the task Horizontally at 36in. Within space at the task Within space at the task Horizontally at 36in, At floor Within space at the task Within space at the task Within space at the floor Within space at the floor Within space at the floor Within space at the floor Within space at the task Horizontally at 36in, Within space at the floor Within the space Lighting sources should not be visible on the vertical surface of video display terminals or on the horizontal surface of tables Recommended level 70 ESI 30fc 30 ESI 50fc 70 ESI 70 ESI 70 ESI (overall) 30fc 30 ESI 75 ESI 10-15~ 30fc 10 ESI 30fc 15fc 75 ESI 30 ESl (general level) 10 ESI 20 ESI 20 ESI 15 ESI 100 ESI (no CRT use) 70fc 15 ESI 10 ESI 371