Reading 4_Gordon

Reading 4_Gordon - About the cover photograph The developer...

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Unformatted text preview: About the cover photograph: The developer of this midtown-Manhattan residential tower wanted to lure young, affluent apartment seekers to a less-than-glamorous neighborhood. He relied on architecture to do it. The lighting concept reinforces the architect's asymmetrical, "anti-classical" approach: there is no traditional bottom- middle-top. The white, plaster wall is lighted with floor-mounted 100PAR/HIR lamps 12" on center. A rough, industrial, Italian, factory floor lamp is paired with a soft, Japanese, paper-shade pendant to contribute to the residential scale. The building fully rented 6 months after the lobby’s completion, 18 months ahead of schedule. Gary Gordon received the 2000 Illuminating Engineering Society Lumen Award and the 2000 lntemational Illuminating Design Award for this project. The New Gotham Lobby, Stephen Alton Architects. Photo by Eduard Hueber. Interior Lighting for Designers FOURTH EDITION Gary Gordon FIES, FIALD, LC Illustrations by Gregory F. Day John Wiley & Sons, Inc. 42 INTERIOR LIGHTING FOR DESIGNERS highlights via the dispersion of “white” light Into the rainbow of colors that comprise it (see color plate 8). The presence of sparkle, highlight, and shadows constitutes the chief visual attrib- \ utes that make a sunny day interesting and stimulating; their absence makes a cloudy, overcast day flat and dull. The emotional stimulation provided by carefully controlled sparkle, highlight, and shadows is equally significant in interiors. Color Color is not a physical property of the things we see—it is the consequence of light waves bouncing offor passing through various objects. The color of an object or surface is deter- mined by its reflected or transmitted light. Color is not a physical property of the things we see—it is the consequence of light waves bouncing off or passing through various objects. What is perceived as color is the result of materials reflecting or transmitting energy in particular regions of the visible spectrum. Green glass transmits the green portion of the spectrum, absorbing almost all of the other regions; yellow paint reflects the yellow portion, absorbing almost all other wave- lengths (figure 4.1). White or neutral gray materials reflect all wavelengths in approxi- mately equal amounts. Pure spectral colors are specified by their wavelength, which is usually expressed in nanometers. A nanometer (nm) is one bil- lionth of a meter or about thirty-nine bil- lionths of an inch. The reflectance chart (color plate 9) shows that butter absorbs blue light and reflects a high percentage of all other colors; these other colors combine to produce what we call yellow. Green lettuce reflects light with wavelengths primarily in the 500—600- nm region and absorbs all of the energ/ at other wavelengths. A tomato is red only because it reflects visible energy at 610 nm while absorbing almost all of the other wave- lengths. A light source that emits radiant energy comparatively balanced in all visible wave- lengths appears "white" in color. Passing a narrow beam of this white light through a prism separates and spreads the individual wavelengths, allowing the eye to distinguish among them. The resulting visual phenome- non is called a color spectrum (color plate 2). “White” light sources emit energy at all or almost all visible wavelengths, but not always in an ideal proportion. Almost all sources are deficient at some wavelengths yet still appear to be white. This deficiency influences the perception of colors; the effect is known as color rendition. It causes the graying of some colors while enhancing the vividness of others. To provide accurate color perception, a light source must emit those wavelengths that a material reflects. Lighting a tomato’s surface with a white light source makes the INTERIOR LIGHTING FOR DESIGNERS white light source YELLOW SURFACE red, green, and blue light absorbed Figure 4.1 To provide accurate color rendition, the light source must emit the wavelengths that the object reflects. surface appear red, because only red wave- lengths of light are reflected toward the eye. All other wavelengths are absorbed. If the tomato is lighted with a green source, however, it will appear dark gray because no red energl is available to be reflected. The eye can see only the colors of a surface that are present in the source of illumination (color plate 10). Because the proportion of colors in “white” light varies, what we call white light is a broad category. Within this category, the most common variations are described as “warm” or “cool.” A warm white light empha- sizes the long (high nm) end of the spec- trum, with hues of yellow through orange to 44 red. Warm light sources that emphasize these hues include the sun and incandes- cent, tungsten-halogen, and high-pressure sodium lamps. Conversely, a cool white light source emphasizes the short (low nm) end of the spectrum, with hues of blue through green to yellow. Cool light sources that emphasize these hues include north skylight and many fluorescent and metal halide lamps. Spectral distribution charts, available from lamp manufacturers, express the rela- tive color composition of light sources (color plates 13—17 and 19—31). Because these charts are of limited practical value in pre- dicting how colors will appear, simplified sys- tems of color notation and color rendition have been developed. COLOR TEMPERATURE Color temperature describes how a lamp appears when lighted. Color temperature is measured in kelvin (K), a scale that starts at absolute zero (—273°C). At room temperature, an object such as a bar of steel does not emit light, but if it is heated to a certain point it glows dull red. Instead of a bar of steel, physicists use an imaginary object called a blackbody radiator. Similar to a steel bar, the blackbody radiator emits red light when heated to 800 K; a warm, yellowish “white” at 2800 K; a day- light-like white at 5000 K; a bluish, daylight white at 8000 K; and a brilliant blue at 60,000 K. The theoretical blackbody is nec- essary because the bar of steel would melt at these higher temperatures. Color temperature is not a measure of the surface temperature of an actual lamp or any of its components. Color temperature refers to the absolute temperature of the laboratory blackbody radiator when its visible radiation matches the color of the light source. Incandescent lamps closely resemble blackbody radiators in that they emit a contin- uous spectrum of all of the visible colors of light (color plate 13). Consequently, the incandescent spectrum is accurately speci- fied by color temperature in kelvin. Fluores- cent and high-intensity discharge (HID) lamps produce a discontinuous spectrum with blank areas punctuated by bands at specific fre- quencies (color plates 1417 and 19—31). These bands combine to give the impression of “white” light; fluorescent and HID lamp color appearance is specified by its apparent or correlated color temperature (CCT). Incandescent lamps used in architec- tural lighting have color temperatures in the 2600 K to 3100 K range; fluorescent lamps COLOR are available with apparent color tempera- tures from 2700 Kto 7500 K; north skylight is arbitrarily called 10,400 K. Unfortunately, the apparent color tem- perature of discontinuous spectrum light sources fails to provide information about its spectral energy distribution. For example, warm white and RE-930 fluorescent lamps have the same apparent color temperature, yet their spectral distribution curves and their color rendition of objects and materials are vastly different. This same limitation applies when using color temperature nota- tions for high-intensity discharge sources, including mercury vapor, metal halide, and high-pressure sodium lamps. COLOR RENDERING To remedy this limitation, color rendering expresses how colors appear under a given light source. For example, a shade of red will be rendered lighter or darker, more crimson or more orange, depending on the spectral- distribution properties of the light falling on it. The most accepted method to deter- mine the color—rendering ability of a light source is a rating system called the Color Rendering Index (CRI). The CRI first establishes the real or apparent color temperature of a given light source. Then, it establishes a comparison between the color rendition of the given light source and of a reference light source. If the colortemperature of a given source is 5000 K or less, the reference source is the blackbody radiator at the nearest color temperature. If the given color temperature is above 5000 K, the reference source is the nearest simulated daylight source. The comparison is expressed as an Ra factor, on a scale of 1 to 100, which indi- cates how closely the given light source matches the color-rendering ability of the reference light source. Since the reference for CRI changes with color temperature, the 45 INTERIOR LIGHTING FOR DESIGNERS CRls of different lamps are valid only if they have similar correlated color temperatures. Therefore, it is inappropriate to compare two light sources unless their color temperature is similar—within 100 K to 300 K. For example, a 3000 K RE-70 fluores- cent lamp and a 6500 K "daylight" fluores- cent lamp render objects differently, despite the fact that they both have a CRI of 75. This occurs because the CRl for the 3000 K lamp was compared to a blackbody radiator and the CRl for the 6500 K lamp was based on comparison to actual daylight. Ra is an average of the color rendering ability of eight test colors; better performance at some wavelengths is concealed when averaged with poorer performance at other wavelengths. As a consequence, two lamps that have the same color temperature and CRl may have different spectral distributions and may render colored materials differently. Some typical CRls appear in table 1 in the appendix. The color properties of the light source significantly alter the appearance of people. Because incandescent sources are rich in red wavelengths, they complement and flat- ter complexions, imparting a healthy, ruddy, or tanned quality to the skin. Cool fluores- cent and HID sources that emphasize the yellow or blue range produce a sallow or pale appearance. SUBJECTIVE IMPRESSIONS The color of light has a profound effect on subjective impressions of the environment. The Amenity Curve indicates that warmer light is desirable for low luminance values (figure 4.2). It also shows that a room uni- formly lighted to 20 footcandles (fc) will be unpleasant with either kerosene lamps (about 2000 K) or lamps that simulate day- light (about 5000 K). With the warm-toned kerosene source, the quantity will seem too high and the 46 space too greatly lighted. With the simulated daylight source, the same quantity of light will seem dark and dingy. Both warm fluores- cent (2700 K or 3000 K) and standard incandescent lamps (2600 Kto 3100 K) fall within the acceptable range on the chart. In addition, a warm atmosphere sug— gests friendliness or coziness. A cool atmo- sphere implies efficiency and neatness. Flynn evaluated subjective responses to colors of white light that are produced by electric light sources in interior spaces at intermediate illuminance values. Flynn’s subjects categorized their impres- sions of visually warm versus visually cool space as follows: cool colors (4100 K) stim- ulate impressions of visual clarity; warm colors (3000 K) reinforce impressions of pleasantness, particularly when a feeling of relaxation is desirable. Flynn found that diffuse light plus warm (orange-red) hues intensify impressions of tension and anxiety. Diffuse light plus cool (violet-blue) hues reinforce impressions of somberness; at low luminance values, they create an impression of gloom. He also found that patterns of sparkle plus saturated warm (orange-red) hues strengthen impressions of playfulness and merriment; this is particularly strong with random patterns of light and color. Patterns of sparkle plus saturated cool (violet-blue) hues reinforce impressions of enchantment; this is particularly strong with rhythmic or regimented patterns of light and color. SURFACE FINISHES AND COLOR OF LIGHT To reiterate: light does not have color, and objects do not have color. Color resides in the eye/brain system. The relationship between the spectral distribution of light and the colors of fabrics, walls, and other elements in the interior is, therefore, pivotal. Some objects appear to 5.000 COLORS APPEAR UN NATURAL 500 Fontcandles (I! O 2000 COLOR COLORS APPEAR DIM OR COLD 2500 3000 4000 5000 10,000 Color temperature in kefvin Figure 4.2 Amenity Cunre, based on a pilot study by A. A. Kruithof. 1941. be the same color under a certain light source although they are different in spectral composition. If the light source is changed, however, the object color differences become apparent (color plate 11). It is advisable to appraise, match, and specify colored materials using light sources identical in color to those that will be used in the completed installation. When the lighting system that will be installed is unknown, two light sources of different spectral character may be used to examine the samples: one of the sources should be predominantly blue in spectral distribution, such as a daylight fluo- rescent lamp, and the other predominantly red, such as an incandescent lamp. andescent Sources INTERIOR LIGHTING FOR DESIGNERS 1000 footlamberts 0‘4 Figure 3.29 Acceptable luminance values decrease as the source approaches the center of the visual field. of automobile headlights at night demon- strates that glare for the approaching driver is a function of direction as well as intensity. It also demonstrates that glare may be present in an environment with little light. Glare is also a function of luminance area. Although a small area of luminance is tolerable, a larger area of the same intensity becomes uncomfortable. It is desirable to reduce luminance intensities as the area of luminance becomes more dominant in the field of view. In addition, glare is a function of loca- tion. Within limits, the human eyebrow con- ceals glare from overhead luminaires, but not from poorly shielded, wall-mounted luminaires or high-luminance wall surfaces, as these elements are directly in the field of view (figure 3.29). 36 90° 450 footlamberts 225 footlamberts .___oo__ .__9 Normal line of sight Direct Glare The late afternoon sun and an unshielded electric light source are examples of the dis- tracting influence of direct glare in the envi- ronment. Direct glare is caused by the lighting system; it is defined as excessive light misdirected toward the eye. Usually, the uncontrolled luminance of an exposed light source produces glare. For this reason, bare lamps (the technical word for light bulb) are rarely used in architectural applications (figure 3.30). When direct glare occurs in the normal field of view, three main control techniques are available. One is to limit the amount of light emitted in the direction of the eye (figure 3.31). Shielding devices such as the hand, used instinctively, and sun visors improve visi- bility and restore visual comfort in this way. Electra WBV magnetic Spectrum elength in Nanometers (10 Angstroms = 1 Nanometer) . ‘3 1x105 1x10 0.1 10 1.000 infrared 1x105 1x107 1x109 1x1011 1x10‘3 1x1015 500 550 600 250 300 350 400 450 /¢; ///,’ "unannouuuuno... Optical Prism _Plate 2 MIXTURES OF LIGHT 650 (Additive primaries) Plate 3 T00 750 1,000 1,500 2,000 3,000 4,0005,000 infrared coo....‘ Ultraviolet Plate 4 MIXTURES OF PIGMENTS (Subtractive primaries) Plate 7 PERCENT REFLECTANCE 400 500 600 790 WAVELENGTH (Nanometers) Natural Daylight Incandescent Lumcnh nm Plate 8 5 I u-II'. POL: Plate 13 (300' White Fluorescent COO' White Deluxe Fluorescent - ' Fluorescent RE-835 Fluorescent RE-84l 'b 000 - =30 -o 0 . 0' 00 '1 .'/ 10m“ l,umm\:-) l | l | l l | (u\\’/ lUIun/Lurncnsl l (“W/10mm Lumcns) .221: .w m.- '—:;.r.‘x:unl | : .:- rm: r-‘.-.L Ramon: P(I'.'..3 lel‘ tl’o': 1;. . _L /\—/ u- .. ._ II_ _ .. ' . . H . _ ..... A 0 A .r n50 500 l : 3:: -.30 .100 430 000 0:30 ‘ ‘ T_. 300 350 ‘ J50 300 550 , . “’I-Inx‘Y I r , ‘ ‘..’.u.ululg.|l lmn) --- tall-“Ll” I'l'” pgallclcngm w") ‘. .‘m‘ulcnglll Hum Warm White Fluorescent wall“ White Deluxe Fluorescent Fluorescent RE-93O Fluorescent RE—950 l l . .1 _ i l {— _ l_ ‘J/lOmII/Unnu' (n‘.'.’/iO-m>/.,\ m-ms. \\ m: (u\\'/ l Omn/Lmnuns) Radiant Pong: m‘. Radium Pm Rnrlmn: Pn'.'.~;! leiunl i‘-.-... 550 ‘.'.’r.;o|:' gm 'nm) ‘.'.‘1~.elength Am) Plate 16 Plate 17 __ p|ate 22 500 ‘.'.'?1‘.L.|ulglh (run) "*> mgth (um) Fluorescent RE-83O High—Pressure Sodium SPE'chALLY BALANCED” WHITE LIGHT R .m ml P\ l r (m /lOnn\/l m n ) lx‘nrlmm Puxaul |u\‘.‘/ [Ulllll/lJlllI-Hlb) RELAT/ VE SENS/T/V/Ty 500 5 '.- ‘.. ".. - J'.. "L ' -’.'..‘.I -i."" ‘-:"..2 500 550 500 \‘Jauclcngth (nm) ‘.‘.’;:-.clcnglh [mm lM/A VELENGTH -— M/LL/M/CRONS Plate18 Low-Pressure Sodium BRIGHTNESS lOniii Pox-n u in?) Brightness of approximately 150 candelas per square inch L'um -l uglil min Plate 27 Clear Metal Halide Brightness of approximately 5 candelas per square inch ‘ '.'-.':v ‘Ill‘fill (niii‘, ~ — Plate 29 -- Ceramic Metal Halide : Figure 3.31 Limiting the amount of light emitted Normal line of sight toward the eye. Flgure 3.30 Unshielded lamp luminance for equiv- alent light output. 5 Radian: Pow.- .150 Plate 28 Phosphor-Coated Metal Halide m, l li' Ill Liimw 71- I7 l 0 300 330 .100 ‘lSl‘J Plate 30 37 ...
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This note was uploaded on 09/03/2008 for the course AREN 3540 taught by Professor Vasconez,s during the Winter '08 term at Colorado.

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Reading 4_Gordon - About the cover photograph The developer...

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