Lighting and Acoustics

Light is radiant energy. It radiates equally in all directions and spreads over a larger area as it emanates from its source. As it spreads, it also diminishes in intensity according to the square of its distance from the source.

As it moves, light reveals to our eyes the surfaces and forms of objects in space. An object in its path will reflect or absorb the light striking its surface, or allow it to pass through.

In the past, lighting design focused on technical subjects such as watts per square foot, kilowatt-hours, and footcandles. Sustainable design has brought that world into close contact with lighting concerns such as beauty, appearance, and health and well-being. The gap between the two approaches is closing. The result is sustainable designs that are about energy savings but also include human factors, comfort, and productivity.

Light-emitting diodes (LEDs) are becoming the dominant type of lighting source, due to their energy efficiency and long life. Initially, LEDs tried to imitate other lighting sources, but they are now evolving their own styles. Today's designs include preset and wireless controls and provide personal and programmable lighting.

LED lights have been investigated for health implications of blue light. The Department of Energy (DOE) has found no risk of blue-light hazard in LEDs or any other source used in general lighting applications. However, LED brightness and its blue content may pose harm to infants or people with eye disorders who might not avert their eyes from the light source frequently enough.

Organic light-emitting diode (OLED) luminaires are becoming available in the U.S., with a thin surface that directly emits light. OLED fixtures do not require reflectors, diffusers, or heat sinks. The light is gentle, as though passing through a paper screen, so spotlights are not possible.

The homelike feel of pendants, sconces, and table lamps help create a human scale in an interior, although the predominance of long real estate leases makes it impractical to avoid lighting trends that might become outdated.

Light sources such as the sun, stars, and electric lamps are visible to us because of the light they generate. Most of what we see, however, is visible because of the light that is reflected from the surfaces of objects. Our ability to see well—that is, to discern shape, color, and texture, and to differentiate one object from another—is affected not only by the amount of light available for illumination but also by the following factors:

• Brightness
• Contrast
• Glare
• Diffusion
• Color

Light reveals the shape, color, and texture of objects.

Even though these objects may be uniformly illuminated, their surfaces differ in brightness according to their color value and texture and, consequently, their ability to reflect light.

Brightness = Illumination × Reflectance

Brightness refers to how much light energy is reflected by a surface. The degree of brightness of an object, in turn, depends on the color value and texture of its surface. A shiny, light-colored surface will reflect more light than a dark, matte, or rough-textured surface, even though both surfaces are lit with the same amount of illumination. Generally speaking, visual acuity increases with object brightness. Of equal importance is the relative brightness between the object being viewed and its surroundings. To make its shape, form, and texture discernible, some degree of contrast or brightness ratio is required. For example, a white object on an equally bright white background would be difficult to see, as would a dark object seen against a dark background.

Contrast in brightness aids our perception of shape and form.

Contrast between an object and its background is especially critical for visual tasks that require the discrimination of shape and contour. An obvious example of this need for contrast is the printed page, where dark letters can best be read when printed on light paper.

For seeing tasks that require the discrimination of surface texture and detail, less contrast between the surface and its background is desirable because our eyes adjust automatically to the average brightness of a scene. Someone seen against a brightly illuminated background would be silhouetted well, but it would be difficult to discern that person's facial features.

The surface brightness of a task area should be the same as its background, or be just a bit brighter. A maximum brightness ratio of 3:1 between the task surface and its background is generally recommended. Between the task area and the darkest part of the surrounding room, the brightness ratio should not exceed 5:1. Higher brightness ratios can lead to glare and associated problems of eye fatigue and loss in visual performance.

High background brightness is helpful in delineating shape and outline.	To aid in discriminating surface detail, surface brightness must be increased.

Surrounding area (3) should range from to 5 times the brightness of the task area (1).

The maximum recommended brightness ratio between the visual task area (1) and its immediate background (2) is 3:1.

Contrasting brightness levels can be desirable in certain situations.

Direct glare is caused by the brightness of light sources within a person's normal field of vision.

Reduce the brightness ratio between the light source and its background.

Use well-shielded or baffled light fixtures that minimize a direct view of bulbs or lamps.

Although our eyes prefer even lighting, particularly between a task surface and its background, our eyes are able to adapt to a wide range of brightness levels. We can respond to a minimum brightness ratio of 2:1 as well as to a maximum of 100:1 or more, but only over a period of time; our eyes cannot respond immediately to extreme changes in lighting levels. Once our eyes have adjusted to a certain lighting level, any sudden significant increase in brightness can lead to glare, eyestrain, and impairment of visual performance.

There are two types of glare, direct and indirect. Direct glare is caused by the brightness of light sources within our normal field of vision. The brighter the light source, the greater is the glare potential. Possible solutions to problems of direct glare include the following:

• Locate the sources of brightness out of the direct line of vision.
• If this is not possible, use properly shielded or baffled lighting fixtures.
• In addition, raise the background brightness of the light sources and reduce the brightness ratio.

Perhaps the greatest potential problem with LEDs is glare. Bare LEDs can exceed the maximum acceptable luminance of any light source. Glare problems with LEDs can be solved with combinations of shielding, refraction, diffusion, indirect lighting, and illumination of adjacent surfaces to reduce contrast. Many of the fixtures being designed and sold today deal with glare problems, which should be considered for all LED fixtures.

Possible Solutions to Glare

Locate light fixtures out of the direct-glare zone.

Indirect glare is caused by a task or viewing surface reflecting light from a light source into the viewer's eyes. The term veiling reflection is sometimes used to describe this type of glare because the reflection of the light source creates a veiling of the image on the task surface and a resultant loss of contrast necessary for seeing the image.

Indirect glare is most severe when the task or viewing surface is shiny and has a high specular reflectance value. Using a dull, matte task surface can help alleviate—but will not eliminate—veiling reflections.

Possible solutions to problems of reflected glare include the following:

• Locate the light source so that the incident light rays will be reflected away from the viewer.
• Use indirect lighting fixtures, or ones with diffusers or lenses that lower their brightness levels.
• Lower the level of general overhead lighting and supplement it with localized task light closer to the work surface.

Glitter and sparkle are desirable types of glare.

Reflected glare affects our ability to perform critical seeing tasks, such as reading or drawing.

	Low-level ambient lighting supplemented by individual task lighting, which is adjustable by the user, is a good general-purpose solution.
Bright, concentrated light sources above and forward of the task surface can cause veiling reflections.

Diffuseness is a measure of a light's direction and dispersion as it emanates from its source. This quality of light affects both the visual atmosphere of a room and the appearance of objects within it. A broad source of light, such as direct/indirect fluorescent fixtures suspended below the ceiling, produces diffused illumination that is flat, fairly uniform, and generally glare-free. The soft light provided minimizes contrast and shadows; however, it can make the reading of surface textures difficult.

On the other hand, a concentrated source of light, such as a spotlight, produces a directional light with little diffusion. Directional lighting enhances our perception of shape, form, and surface texture by producing shadows and brightness variations on the objects it illuminates.

Although diffused lighting is useful for general vision, it can be monotonous. Some directional lighting can help relieve this dullness by providing visual accents, introducing brightness variations, and brightening task surfaces. A mix of both diffused and directional lighting is often desirable and beneficial, especially when a variety of tasks are to be performed in a room.

Diffused illumination minimizes contrast and shadows.

Directional lighting enhances the modeling of form and texture.

Another important quality of light is its color and the way it affects the coloration of objects and surfaces in a room. We assume most light to be white, but the spectral distribution of light varies according to the nature of its source. Noon daylight is considered to be the most evenly balanced white light; in the early morning hours, daylight can range from purple to red. As the day progresses, it will cycle through a range of oranges and yellows to blue-white at noon, and then back again through the oranges and reds of sunset.

The spectral distribution of electric light sources varies with the type of lamp. For example, an incandescent lamp produces a yellow-white light, while a cool-white fluorescent produces a blue-white light.

The apparent color of a surface is a result of its reflection of its predominant hue and its absorption of the other colors of the light illuminating it. The spectral distribution of a light source is important; if certain wavelengths of color are missing, then those colors cannot be reflected and will appear to be missing or grayed in any surface illuminated by that light.

Earlier LED products had difficulty delivering uniform white light with consistent color rendition. Today, institutions including the Illuminating Engineering Society (IES) have proposed new color rendering metrics more attuned to the unique characteristics of LEDs.

The source of all natural daylight is the sun. Its intense light varies with the time of day, from season to season, and from place to place. It can also be diffused by cloud cover, haze, precipitation, or any pollution that may be present in the air.

In addition to direct sunlight, two other conditions must be considered when designing the daylighting of a space: reflected light from a clear sky and light from an overcast sky. While direct sunlight emphasizes hot, bright colors, skylight is more diffuse and enhances cool colors.

Until 2013, when the IES adopted and published the testing and calculation guide Lighting Measurement 83 (LM-83), Approved Method: IES Spatial Daylight Autonomy (sDA) and Annual Sunlight Exposure (ASE), equitable comparisons of daylight performance were not possible. LM-83 was the first IES-adopted evidence-based annual daylighting performance metric in the lighting industry. Now incorporated in lighting analysis and design software packages, sDA and ASE (also known as climate-based daylight metrics or dynamic-daylight metrics) increase the rigor and complexity of daylighting design consultation and building performance assessment.

Circadian rhythms are a biological system that involves melatonin (the hormone that triggers sleep cycles). The main regulator for the circadian rhythm is light, although nighttime activity and other factors can also affect it. As the sun sets and darkness increases, melatonin increases and starts to calm our body down to prepare for sleep as part of a natural rhythm.

Today people may spend both day and night indoors, and a person can spend an entire day without direct contact with sunlight. We may not use our circadian rhythms to tell us when to sleep and when to be awake. Providing access to daylight in most offices may, for example, involve moving perimeter offices into the building's core.

The blue light in LEDs is more effective at suppressing melatonin. With color-tunable LEDs, bright daylight can be shifted to warmer, yellower lighting later in the day, helping to prepare people to sleep when they get home. Concentrated LED lighting, when used inappropriately, can be harmful to certain populations. Research into the amount and type of lighting that is desirable continues. Introducing sunlight into a building can decrease dependence on artificial lighting, which in turn reduces lighting energy use. Sunlight will also bring solar heat into the building, which may result in energy savings in cold weather but can increase air-conditioning costs in warmer months.

For the many regions of the world with little or no access to an electrical grid, a solar-powered charging device can provide over 150 hours of LED illumination from 7.5 hours in bright sunlight.

Glare

A problem associated with daylighting is glare caused by excessive contrast between the brightness of a window opening and the darker wall surfaces or cast shadows adjacent to it. The placement of windows is as important as their size when dealing with glare. The optimum condition is balanced lighting from at least two directions—from two walls or a wall and the ceiling. Skylights, in particular, can help soften the harshness of direct sunlight.

In rooms with windows close to the floor, glare can be caused by the light reflected off the exterior ground surface. This ground glare can be reduced through the use of shade trees or a screen of horizontal louvers. Interior window treatments can also be used to diffuse or block glare.

Bidirectional lighting—lighting from two directions—raises the level of diffused light in a space and reduces the possibility of glare.

Glare results when our eyes cannot adjust simultaneously to widely contrasting areas of brightness. Our eyes adjust to the brightest light in our field of vision, reducing our ability to discern less brightly lit areas.

High window openings allow daylight to penetrate more deeply into an interior space and help to reduce glare.

Windows set flush in a wall or ceiling accentuate contrasts between the bright exterior and the darker interior surfaces. Deep-set windows, splayed jambs, and rounded jambs can soften this contrast.

Locating a window adjacent to a perpendicular wall or ceiling surface maximizes the light entering the window. The perpendicular surface is illuminated by the entering light and becomes itself a broad source of reflected light. The use of wall and ceiling finishes with high levels of reflectance, such as white paint, helps to bounce reflected light deeper into an interior space, reducing the amount of electric lighting needed and saving energy.

A light shelf is an exterior horizontal construction located below the head of a window opening and typically just above eye level. The light shelf shades the lower portion of the window from direct sunlight and reflects daylight onto the ceiling of the room, diffusing light deeper into the space.

Skylights are glazed with clear, patterned, or translucent glass, or with clear, gray-tinted, or milk-white acrylics. Skylights can be fitted with remote-control window treatments that diffuse light and reduce the transmission of solar heat.

Flat skylights may be prone to leaks and dirt accumulation.

Domed or slanted skylights stay cleaner and tend to leak less.

Tubular skylights (light tubes) collect sunlight through a small, clear acrylic dome on the roof, transmit it though a cylindrical shaft, and disperse it through a translucent diffuser lens into interior spaces.

Light is the prime animator of interior space. Without light, there would be no visible form, color, or texture, nor any visible enclosure of interior space. The first function of lighting design, therefore, is to illuminate the forms and space of an interior environment, to enable users to undertake activities and perform tasks with appropriate speed, accuracy, and comfort. Interior lighting can effectively guide the viewer through a space or series of spaces and direct the viewer's gaze to points of interest. Lighting also provides security through the illumination of spaces and any potential hazards.

Lighting Patterns

Poorly placed or irregularly scattered lighting fixtures contribute to distracting visual clutter. Carefully organized lighting patterns emphasize architectural features, provide cues to the use and orientation of the space, and support the designer's intent. Lighting layout drawings coordinate lighting fixture locations with sprinkler heads, air diffusers, return grilles, smoke detectors, loudspeakers, and other ceiling elements.

Lighting design has entered a new era, with solid-state lighting fitting into a broad context of systems that have the ability to gather and transmit all types of data at an unprecedented scale. Innovation is no longer primarily about seeing new products with their new shapes and styles. Lighting has become less about the fixture and more about software and controls. New technologies such as LED lighting can require significant technological study on the designer's part and thus result in the loss of time available to focus on lighting design.

Lighting designers have responded to the emergence of LED lighting with self-education about solid state lighting products and project-time learning. They advocate field-measurable metrics such as candlepower, correlated color temperature, CRI and other values, flicker, and beam spread as criteria for testing and gauging product performance.

LEED did not originally include lighting design in its requirements. Lighting designers had advocated for sensible energy codes, and, as LEED gained influence, many lighting designers adopted LEED design principles and aided in the refinement of lighting-related credits in early versions of LEED. LEED's popularity has raised the awareness of lighting as a major component of energy-efficient and environmentally responsible design.

Interior lighting enables us to see forms, navigate space, and perform tasks. Lighting design is a process of integrating light with the physical structure of the building, the designer's concept for the interior space, and the functional uses of the space. It begins with thinking about light, not product. Lighting design education should promote a wider literacy about light across all disciplines so that designers can focus on the lighting design practices that are relevant today.

Brightness Balance

Vertical surfaces are the most visually conspicuous features in a space. Lighting should preserve the integrity of vertical planes, highlight special features or finishes, and avoid spatial distortions such as scallops on walls. Strategies include the following:

• Light opposite walls of a space.
• Wallwashers on one wall can be mixed with nonuniform lighting on the other.
• Balance perimeter illumination of a space with its center.
• Lighting horizontal surfaces within a space emphasizes detail, people, and movement, and de-emphasizes the architecture.
• Illuminate vertical and overhead surfaces to emphasize architectural form.

Recently, manufacturers have developed ways to integrate lights into architectural surfaces. These include illumination of floors with patterns or wayfinding signs, ceiling applications that provide surfaces of light, and prefabricated sheet-metal panels with built-in LEDs that enliven walls with a variety of visual effects. Both standard and custom designs are available; keeping records of a design is suggested so that panels can be easily replaced.

Luminance Ratios

Luminance differences are specified as a ratio between one luminance and another.

• Vary luminances at some points in the space to increase visual interest and prevent eye fatigue.
• Computer screens tend to reflect bright areas, although this is less of a problem than in the past, thanks to brighter screens with better angle adjustments. Indirect lighting fixtures also help with this problem.

Shadows

Patterns of light and shadow create visual interest by rendering the texture and three-dimensional form of objects.

Occupancy sensors detect activity within a certain area and turn lights on automatically when someone enters a room. They reduce lighting energy use by turning lights off soon after the last occupant has left the room.

Energy Efficiency

The U.S. Energy Information Administration (EIA) estimates that in 2016 about 10 percent of total electricity consumed by both the residential and commercial sectors in the U.S. was used for lighting; this was about 7 percent of total U.S. electricity consumption. Building codes limit the number of watts available for lighting. Energy conservation criteria are increasingly driving the selection of light sources, the quantity and type of lighting fixtures, and the specification of lighting controls. Consequently, designers must be aware of energy use as they design lighting.

• Use available watts to supply light where and when needed; limit unwanted light.
• Integrate and control daylight in the space.
• Choose light sources carefully, and locate them with discretion.
• Control lighting with dimmers, timers, and occupancy sensors.

Upgrading from conventional controls (on-off, occupancy, and dimming) to video and sensor technologies that make a building truly smart is a logical move from putting in single-purpose systems that will very soon become obsolete. Wireless controls and sensors have been designed in fixtures themselves, avoiding the need for separate installation. Integrating software streamlines the equipment required for building systems while reducing the physical space needed for installation.

Illuminance is the measure of incident light (i.e., the light falling) on a surface. Illuminance does not determine how bright a surface will appear; a dark surface will not reflect as much of the light that falls on it as a light one. The conditions of a specific task, as well as the visual acuity of the viewer, determine the required level of illuminance.

The electric light sources used in lighting fixtures are called lamps. The quantity and quality of light produced differ according to the specific type of lamp used. The light is further modified by the housing that holds and energizes the lamp and any reflector, lens, or baffle used to control how the light is distributed, diffused, or shielded.

The color rendering index (CRI) rating is a measure of a lamp's ability to render color accurately when compared with a reference light source of similar color temperature. Manufacturers are working to improve the CRI of all light sources, so that good color rendering can be achieved while maintaining efficiency. However, the best way to check an LED light source's blue emission, light output, and other color rendering abilities is with a spectometer, rather than relying on CRI or CCT ratings.

The IES TM-30 color fidelity metric (Rf) is a substantial improvement over CRI, due to its use of 99 color samples, a more-uniform color space, and calculations that fit and express real-world conditions better. Although this still does not provide all that is needed to fully consider color rendering, when used with the procedure's color distortion icon, the addition of TM-30s color gamut metric (Rg) heightens an understanding of how a light source will reveal color.

Light sources have traditionally been classified as warm or cool, and specific light sources were often available in only a single color. Today, there are a variety of light sources with a wide range of apparent colors, including fluorescent and LED lamps. With the arrival of multicolor emitter arrays and other blended LED source options, white light and its color rendering abilities can be designed to a particular project need, according to Randy Burkett, FIALD, FIES, of Randy Burkett Lighting Design, St. Louis (Architectural Lighting, November/December 2016).

The correlated color temperature (CCT) is a reference standard that correlates to a standard color and is identified in kelvins (K). The higher the number, the cooler is the light source, and vice versa.

Efficacy is a measure of the efficiency of a light source, measured in lumens per watt. A lumen is a measure of the amount of light emitted by a light source or falling onto a surface, regardless of directionality.

Color Rendering Index (CRI) of Various Light Sources

CRI	Light Source
100	Noon sunlight; average daylight
93	500-watt incandescent
89	Cool-white deluxe fluorescent
78	Warm-white deluxe fluorescent
62	Cool-white fluorescent
52	Warm-white fluorescent

Correlated Color Temperature (CCT)

CCT in Kelvins	Light Source
2700	Incandescent
3000	Halogen
2700–6500	Fluorescent
3000–4000	Metal halide
2800–6000	LED
5500–7500	Daylight

Light-emitting diodes (LEDs) radiate very little heat and are highly energy-efficient. LEDs have an extremely long life, typically about ten years. High-powered white-light LEDs are used for illumination. They are insensitive to vibration and temperature, are shock resistant, and contain no mercury. The tiny ⅛-inch (3-mm) lamps can be combined into larger groups to mix colors and increase illumination. LEDs operate on DC voltage, which is transformed into AC within the fixture.

LEDs are used for both residential and commercial lighting. Today, LEDs are being designed for most lighting purposes. They can be designed to focus light, and are widely used for task lights. LED downlights, panel fixtures, step lighting, and exit signs are also available. Bendable ribbon lights are available to provide even light distribution for curved runs or crisp right angles.

LEDs are designed to use less energy and have lower watts ratings. Watts are a measure of energy use, so watts are not used to determine the brightness of LEDs. The higher the lumen (lm) rating, the brighter the bulb will be. For example, a 6- to 9-watt LED has a 450 lm rating, equivalent to a 40-watt incandescent. A 25- to 28-watt LED has a 2600 lm rating, equivalent to a 150-watt incandescent.

A potential problem with LEDs is thermal management. High heat loads can reduce an LED's phosphors that are used to convert blue and violet light to white light, degrade the color of optical-grade silicone, and shorten diode life spans. Unmanaged, these effects depreciate lumens over an LED's lifetime, and cause color change. Manufacturers learned to add heat sinks to their products, which at times added more than 50 percent to a fixture's overall weight, increasing material use and shipping costs, and resulting in bulkier designs. More recent designs are much more sophisticated, resulting in lighter and sleeker fixtures that use lighter aluminum, ceramic, or other materials for heat sinks. Even more recently, LED fixtures are being made with the heat sink integrated into the design of the fixture, or with cross-flow ventilation that whisks heat away from the LEDs. Some fixtures have been designed with fans, but these run the risk of overheating should the fan fail.

Some LED problems arise from lack of compatibility with fixture components and controls from both legacy and solid-state lighting manufacturers. The continuously changing nature of LED technology has made it almost impossible to develop a set of technical standards. As use of LED lighting continues to spread, solutions to these problems can be expected to develop.

LED step lighting

Comparative Lamp Efficiencies

Lamp Type	Lumens/Watt
100–200 W incandescent (230 V)	13–15
100–200–500 W tungsten halogen (230 V)	16–20
5–40–100 W incandescent (120 V)	5–18
T12 fluorescent tube, electronic ballast	60
9–32 W compact fluorescent	46–75
T8 fluorescent tube, electronic ballast	80–100
Spiral fluorescent tube, electronic ballast	114–124
Metal halide lamp	65–115
High-pressure sodium lamp	85–150

LED strip

LED RibbonLyte striplighting by Acolyte Lighting

LED fixtures

The standard T12 lamp is now considered outdated, replaced by T8 lamps.

T8 and T5 Lamps

• Better color rendering than standard T12.
• T5 has better lighting efficiency than T8 or T12.
• Smaller tube diameters than T12.
• T5 lamps are smaller than T8, but produce roughly the same amount of light, making glare an issue.

Compact Fluorescent Lamps

• Available from 5 to 80 watts.
• High efficacy (typically 60 to 72 lumens per watt).
• Good color rendering.
• Very long lives (6000 to 15,000 hours).
• Tubular or spiral types.
• Many are available with built-in ballast and screw bases for direct replacement of incandescent lamps.
• Lack of beam control and dimming capability.
• Mercury content.

Discharge lamps produce light by the discharge of electricity between electrodes in a gas-filled glass enclosure. A common type is the fluorescent lamp.

Fluorescent lamps are low-intensity discharge lamps that produce light by generating an electric arc that passes through the mercury vapor sealed within their tubes. This produces ultraviolet light that energizes the phosphors that coat the tubes' inner walls, thus emitting visible light. Because fluorescent lamps contain mercury, they require special handling for recycling. Effective April 15, 2007, U.S. manufacturers in the National Electrical Manufacturers Association voluntarily capped the total mercury content in compact fluorescent lamps (CFLs) less than 25 watts at 5 milligrams (mg) per unit, and those 25 to 40 watts to 6 mg per unit. A broken fluorescent tube will release its mercury content, requiring special procedures for safe cleanup. LEDs, which do not contain mercury, are replacing fluorescent lamps in many applications.

Fluorescent lamps are more efficient and have a longer life (6000–24,000+ hours) than incandescent lamps. They produce little heat and are available in a variety of types and wattages. Common lengths range from a 4-watt T5 at 6 inches (152 mm) to a 125-watt T12 at 8 feet (2438 mm). Fluorescent lamps require a ballast to regulate electric current through the lamp. Some lamps have pin bases, while others have screw-in bases.

With LED replacements for fluorescents relatively new to the market, fluorescent lamps remain a viable option based on performance, lamp-life, and cost. Fluorescents serve as a bridge technology between incandescent lamps and LED solid-state lamps.

Fluorescent lamps are now available in a variety of colors, including warm white, cool white, sunlight, cool daylight, and sky white. Approximate CRI ratings range from 50 to 95, and color temperatures from 2700 K to 8000 K. Dimmable fluorescent lamps are available.

High-intensity discharge (HID) lamps—mercury vapor, high-pressure sodium (HPS), and metal halide lamps—produce light by passing an electrical current through a gas or vapor under high pressure. These lamps have a long life expectancy and consume little energy to produce a great amount of light from a relatively small source. They take several minutes to warm up. Most HID lamps are used primarily for industrial, commercial, roadway, and security lighting. They typically have low to average color rendering. HID lamps are being replaced by LEDs in many applications.

Metal halide lamps are used in spaces with high ceilings where lamps are left on for extended periods. Their start times range from 1 to 20 minutes, depending on the type. Metal halide lamps have excellent color, efficacy, and lamp life. CRIs commonly rate 70 to 90, and CCTs range from 2500 K to 5000.

High-pressure sodium lamps produce a pinkish orange light when warmed. The white SON lamp is a variation on the HPS with a color temperature around 2700 K and a CRI of 85, similar to that of an incandescent light. White SONs are sometimes used indoors in restaurants. However, they have higher purchase costs, shorter lives, and lower light efficiency than other HPS lamps.

Mercury vapor lamps are primarily used outside for parking and security lighting. They are the least efficient of the HID lamps.

Both metal halide and white SON HPS lamps have ellipsoidal bulb shapes.

Incandescent lamps consist of metal filaments that are heated within a glass enclosure until they glow. Incandescent lamps are available from 6 to 1500 watts, and have a low efficacy rating of from 4 to 24.5 lumens per watt. Only about 12 percent of the wattage used goes toward the production of light; the remainder is given off as heat. They also have a comparatively short life of from 750 to 4000 hours. Because of their energy inefficiency, incandescent lamps are being regulated or phased out in several countries, including the U.S.

Tungsten-halogen lamps, also known as halogen or quartz lamps, are incandescent lamps with a small amount of halogen gas sealed inside the bulb. They maintain close to their full output over time. Available from 5 to 1500 watts, they produce 10 to 22 lumens per watt.

While standard incandescent lamps operate on standard-voltage circuits, low-voltage lamps, including tungsten-halogen, operate between 6 and 75 volts. Their design offers more precise beam control, higher efficacy, energy savings where focused light is needed, and 1000 to 6000 hours of life. Although they are more efficient than standard incandescent lamps, they still perform less efficiently than LEDs or fluorescent lamps, and require an AC step-down transformer to lower the power to 12 V. Dimming requires the use of magnetic transformers specially designed for use with low-voltage lighting components. Low-voltage lighting is considered most beneficial for accent or task lighting, but not for ambient lighting.

The optical glass or plastic fibers in fiber-optic lighting transmit light from one end to the other by reflecting light rays back and forth inside their cores in a zigzag pattern. Each small-diameter fiber is protected by a transparent sheath and combined with others into flexible bundles.

Fiber-optic lighting remains a good solution to transmit light from a single bulb that is located discreetly to illuminate stairways or focal points at a distance. They are useful in illuminating museum displays, as the cables themselves do not heat up.

Manufacturers are beginning to coordinate their fiber-optic products so that they are compatible with each other. Acrylic cables are less expensive than glass ones, but may degrade over time. Dust deposited during installation is also a problem.

A fiber-optic chandelier

Light fixtures are integral parts of a building's electrical system, transforming energy into usable illumination. Light fixtures require an electrical connection or power supply, a housing assembly, and a lamp.

We are concerned not only with the shape and form of the fixture but also with the form of the illumination it provides. Point sources give focus to a space, since the area of greatest brightness in a space tends to attract our attention. They can be used to highlight an area or an object of interest. A number of point sources can be arranged to convey rhythm and sequence. Small point sources, when grouped, can provide glitter and sparkle.

Linear sources can be used to give direction, emphasize the edges of planes, or outline an area. A parallel series of linear sources can form a plane of illumination that is effective for the general, diffused lighting of an area.

Volumetric sources are point sources expanded by the use of translucent materials into spheres, globes, or other three-dimensional forms.

A light fixture consists of one or more electric lamps with all of the necessary parts and wiring for supporting, positioning, and protecting them, connecting them to a supply of power, and distributing the light.

Light fixtures can provide direct and/or indirect illumination. The form of distribution depends on the design of the fixture as well as its placement and orientation in a space. Some light sources serve primarily as decorative focal points. Others provide needed light while the fixtures themselves are de-emphasized or hidden.

Recessed lighting fixtures are hidden above the finished ceiling and shine light through an aperture in the ceiling plane. They preserve the flat plane of the ceiling.

Recessed lighting fixtures offer an unobtrusive way to bring light to circulation paths within a larger space, or to provide increased light levels in a specific area. When used indiscriminately throughout a space, however, they can create a monotonously even pattern on the ceiling and a uniform but dull level of illumination.

Downlights are used in multiple arrangements to provide ambient light for a large space, or to offer a focal glow on a floor or work surface. LED downlights are now available. Lamps and accessories for recessed downlights are available in a variety of styles, allowing the designer a range of effects. Some recessed fixtures appear as black holes in a light-colored ceiling when they are turned off. Downlights located too close to a wall can create an unattractive scalloped pattern. Wallwashers are designed to illuminate a matte vertical surface in a more uniform manner. Walls can be illuminated in one of two ways: wallwashing and wall grazing, which vary in the distance of the fixture from the wall surface.

Wallwashers are typically located at least 12 inches from the wall plane, giving the wall texture a flat appearance. For wall grazing, the fixture is positioned very close to the wall—a maximum of 12 inches—to bring out the wall texture. The overall height of the wall determines the fixture's distance from the wall. Adjustable LED wallwashers are available.

The housings of some light fixtures are partially recessed into the ceiling or wall construction, while part of their housing, reflectors, or lenses projects beyond the ceiling or wall surface. The smaller sizes of many LED fixtures allow them to be fully recessed, where larger incandescent models had to be partially recessed.

Fixtures that shine down from above can cause glare on computer screens, especially if the lamps are visible or if the fixture creates a bright area in the darker field of the ceiling. This is less of a problem with the brighter, thinner screens now in use, which are easier to adjust to avoid glare.

Diffusers provide some protection, but suspended fixtures that bounce light off the ceiling and filter light downward as well do a better job of minimizing glare.

The ADA mandates that surface-mounted fixtures that are between 2′3″ and 6′8″ above the floor should not extend more than 4″ into the space.

Cornice lighting directs the light downward from an interior cornice at the edge of a ceiling.

Surface-mounted light fixtures are mounted on the finished ceiling or wall and are usually attached to a recessed junction box. Light fixtures that are mounted directly on a ceiling are generally positioned above the people and furnishings in the room and can spread their light over a broad area.

Wall-mounted light fixtures are often decorative and help to create the ambiance of the space. Wall sconces can shine light upward, downward, or sideways, as well as produce a gentle glow from the fixture itself.

Wall-mounted fixtures can provide task lighting when their illumination is focused on the task area. When shining on a wall or a ceiling, they add to the general illumination of the space. Their horizontal and vertical positions must be carefully coordinated with windows and furnishings. A versatile design for task lighting consists of a lampshade that uses magnets to facilitate its placement anywhere along metal supports.

Cove, valance, and cornice lighting are all methods for illuminating a space indirectly from within an architectural detail or a manufactured fixture. They give a soft, indirect glow to the area they illuminate and are often used to highlight ceiling details or wall textures.

Considerations when designing a cove lighting detail include (Architectural Lighting, March/April 2015):

• Be aware that joints or gaps between lighting fixtures will appear in the pattern of light. Placing fixtures end to end or in a staggered or slanted arrangement can eliminate dark spots at the end of a lamp.
• The top of the lamp should be level with the fascia of the cove to prevent shadow lines.
• Stop a cove short of an end wall to avoid sharp cutoff lines.
• As a cove nears an end wall, keep at least 12 inches clear at inside corners to prevent hot spots.
• The ceiling surface should generally be a high-reflectance matte or satin finish, while the inside surface of the cove should be flat white to minimize specular reflections.
• As the cove's distance from the ceiling plane increases, the uniformity of the ceiling brightness will also increase.

Pendant-mounted light fixtures are attached to either a recessed or surface-mounted junction box concealed by a canopy, and may hang below the ceiling on a stem, chain, or cord. The fixtures may throw light up, down, or at an adjustable angle.

Uplights or indirect lighting fixtures wash the ceiling in light. Some also provide downlight. They may be:

• Suspended from the ceiling
• Mounted on top of tall furniture
• Attached to walls, columns, or floor stands

Track-mounted light fixtures consist of adjustable spotlights or floodlights mounted on a recessed, surface- or pendant-mounted track through which electrical current is conducted. The light fixtures can be moved along the track and adjusted to shed light in multiple directions. Building energy codes may require that each head on the track be counted as a separate fixture.

Chandeliers often provide more sparkle than illumination and become a focal point in the space.

Decorative lights serve as accents within the space. The light they produce may be secondary to the appearance of the fixture, the glowing surface of which draws the eye. Portable lighting fixtures are commonly referred to as lamps, and their light sources as light bulbs.

Desk and task lamps are found in both residential and workspaces. Many are adjustable to accommodate varied tasks and individual preferences. Desk and task lights can help save energy by providing focused light where it is needed, allowing lower levels of ambient lighting.

Table lamps often serve both decorative and practical functions. They become part of the room's décor, while providing either general illumination or task light.

Floor lamps may shine up (torchières), down, or at adjustable angles. Like table lamps, they become part of the décor and can provide either task or general lighting.

Portable lamps help to bring human scale to architectural spaces by creating decorative detail and localized light. They are usually operated at the fixture itself, giving users easy control over their environment.

The layout of lighting fixtures and the pattern of light they radiate should be coordinated with the architectural features of a space and the pattern of its use. Since our eyes seek the brightest objects and the strongest tonal contrasts in their fields of vision, this coordination can serve to reinforce the architectural features and support the function of the space.

For the purpose of planning the visual composition of a lighting design, a light source can be considered to have the form of a point, a line, a plane, or a volume. If the light source is shielded from view, then the form of the light emitted and the shape of surface illumination produced should be considered. Whether the pattern of light sources is regular or varied, a lighting design should be balanced in its composition, provide an appropriate sense of rhythm, and give emphasis to what is important.

Lighting design manipulates the fundamental elements and qualities of ambient and focal lighting as well as sparkle:

• Ambient lighting provides a general, shadowless light level that is restful and minimizes interest in objects and people.
• Focal lighting offers a contrast in brightness that is directive and creates a sense of depth. Examples include task and accent lighting.
• Sparkle—such as highlights, scintillating sequins, crystal chandeliers, and twinkling stars—is stimulating and may be distracting, but it is also often entertaining.

The changes brought to the lighting industry by LED solid-state lighting have caused legacy companies such as Philips, Osram, and GE to reconsider their lighting businesses completely. As this edition of Interior Design Illustrated is being prepared for publication, the dramatic recasting of players once mainstays of the pre-LED era is difficult to track. Even Lightfair, the preeminent event for lighting designers in the U.S., has moved from New York to Philadelphia to San Diego, with a focus on technology more than on product appearance.

Light animates space and reveals forms and textures.

Ambient point sources

Ambient linear sources

Direct/indirect linear sources

Indirect point sources

Indirect linear sources

Ambient or general lighting illuminates a room in a fairly uniform, generally diffuse manner. The dispersed quality of the illumination can effectively reduce the contrast between task lighting and the surrounding surfaces of a room. Ambient lighting can also be used to soften shadows, smooth out and expand the corners of a room, and provide a comfortable level of illumination for safe movement and general maintenance.

Ambient lighting is appropriate for frequently reconfigured spaces and for areas where the location of tasks varies widely. Ambient fixtures may be direct, direct/indirect, or indirect point or linear sources. LED strip-lighting fixtures can provide ambient light.

The addition of task lighting to ambient systems provides a higher level of focal lighting for task areas, with surrounding areas illuminated at a lower level. Task-ambient lighting saves energy, improves the quality of lighting, and gives the user more control.

Focal lighting creates brighter areas within the ambient light levels of a space through the use of task lighting and accent lighting.

Task lighting illuminates specific areas of a space for the performance of visual tasks or activities. The light sources are usually placed close to—either above or beside—the task surface, enabling the available wattage to be used more efficiently than with ambient lighting. The lighting fixtures are normally of the direct type, and adjustability in terms of brightness and direction is always desirable.

To minimize the risk of an unacceptable brightness ratio between task and surroundings, task lighting is often combined with ambient lighting. Depending on the types of lighting fixtures used, focal lighting can also contribute to the general illumination of a space.

In addition to making a visual task easier to see, focal lighting can also create variety and interest, divide a space into a number of areas, encompass a furniture grouping, or reinforce the social character of a room.

Accent Lighting

Accent lighting is a form of focal lighting that creates focal points or rhythmic patterns of light and dark within a space. Instead of serving simply to illuminate a task or activity, accent lighting can be used to relieve the monotony of ambient lighting, emphasize a room's features, or highlight art objects or prized possessions.

Sparkle

Lighting can bring out the highlights in the objects that it shines on or introduce sparkle through the brilliance of the fixture itself. Small, tightly focused lamps reflect dancing bits of light off reflective surfaces. Chandeliers often produce little ambient light—they are all about sparkle.

Lighting technology is advancing about as fast as computer technology. The basic principles of lighting design have not changed, but the available tools have. Energy conservation is a major issue for lighting design, and computer software is available to perform the calculations required by codes. The major challenge today is to minimize lighting energy use without sacrificing quality.

Quantitative recommendations that address lighting design standards include luminance (brightness), illuminance levels, uniformity, and glare. Traditionally, lighting standards have used a quantitative approach of determining how many footcandles are needed. These standards do not reflect qualitative issues, and may result in lighting that is overly uniform and less energy-efficient.

Illuminance is a measure of incident light on a surface. It is measured in lumens per square foot (footcandles) or lumens per square meter (lux). One footcandle is a unit of illuminance equal to one lumen spread evenly over an area of one square foot. This measure of light can be calculated by the lumen method (also called the point-by-point method), or with a more accurate computer program. Today, computer modeling programs model lighted spaces increasingly accurately.

Brightness is our subjective perception of varying degrees of light intensity. Luminance is the amount of light energy that is reflected off a surface and interpreted by our visual system. Interpreting luminance can be technically quite complex, but it is also very intuitive and dependent on experience.

Lighting designers are moving toward a new approach that looks at qualitative design issues such as the following:

• Desired appearance of the space
• Color and luminance of finishes
• Integration of daylighting
• Glare control
• Light distribution on surfaces and the task plane
• Modeling of people and objects, and shadows
• Focus on points of interest
• Lighting system controls

A successful lighting design is determined by the balance of relative luminances rather than by the quantity of illuminance striking the surfaces of a room. Measurements of illuminance, however, are used to select lamps and lighting fixtures and to evaluate a lighting design. The photometric data to be considered include:

• The luminous intensity distribution curve (LIDC) represents the light pattern produced by a lamp or light fixture in a given direction from the center of the light source.
• The coefficient of utilization indicates the efficiency of a light fixture.
• The light loss factor (LLF) reflects the decrease in luminous output that occurs over the operating life of a lamp, which can be affected by the accumulation of dirt on the surfaces of the light fixture and by the effects of temperature.

Light fixtures may be classified according to the way they distribute the light emitted by their lamps. The basic types shown here are based on the percentage of light emitted above and below the horizontal.

Example of a luminous-intensity distribution curve of a direct-concentrating light fixture

Acoustic Principles

Acoustics deals with the production, control, transmission, reception, and effects of sound. In interior design, we are concerned with the control of sound in interior spaces. More specifically, we want to preserve and enhance desired sounds and reduce or eliminate sounds that would interfere with our activities.

Sound occurs when energy is transmitted as pressure waves through the air or another medium. A sound wave travels outward spherically from its source until it encounters an obstacle in its path. When a sound wave strikes an object, it is either absorbed or reflected, or a combination of the two.

In a room, we first hear a sound directly from its source and then from a series of reflections of that sound. Reflective surfaces are useful when they reinforce desirable sounds by directing and distributing their paths in a room. The continued presence of reflected sounds, however, can cause problems of echo, flutter, or reverberation.

Echoes occur in large spaces when surfaces reflect sound waves that are loud enough and received late enough to be perceived as distinct from the source. In smaller rooms, parallel reflective surfaces can cause a rapid succession of echoes we call flutter.

Reverberation refers to the persistence of a sound within a space, caused by multiple reflections of the sound after its source has stopped. Some music is enhanced with long reverberation times, but speech can become muddled in such an acoustic environment. Altering the shape and orientation of a room's surfaces or adjusting the proportion of reflective and absorbent materials can aid sound clarity.

The requirements for sound level, reverberation time, and resonance vary with the nature of the activity and the types of sounds generated. An acoustical engineer can determine the acoustical requirements for a space. The interior designer should be aware of how the selection and disposition of reflective and absorbent materials affect the acoustical qualities of a room.

Acoustical design is becoming integrated into the best design practices, with designers thinking through how to integrate better acoustics into all kinds of spaces earlier in the design process. Some states are adopting new acoustic standards for classroom acoustics. As the population continues to age, hearing issues are taking a greater importance.

Decibel (dB) is a unit expressing the relative pressure or intensity of sounds on a uniform scale, from 0 for the least perceptible sound to about 130 for the average threshold of pain. Because decibel measurement is based on a logarithmic scale, the decibel levels of two sound sources cannot be added mathematically. For example, 60 dB + 60 dB = 63 dB, not 120 dB.

An equal loudness contour is a curve that represents the sound pressure level at which sounds of different frequencies are judged by a group of listeners to be equally loud.

A sone is a unit for measuring the apparent loudness of a sound.

Noise

We refer to unwanted, annoying, or discordant sounds as noise. Noise from outside of a space can be controlled in the following ways:

• Isolate the noise at its source.
• Locate noisy areas as far away as possible from quiet areas.
• Reduce the transmission of sound from one space to another.

Noisy spaces significantly impact the way our brains and bodies function. Excess noise in school environments has been shown to slow cognitive development. In hospitals, noise has been found by a University of Chicago Medical Center study to disrupt the sleep needed for recovery of four out of ten patients. Both LEED and WELL standards take noise into consideration. Office noise can both distract and annoy, and overheard conversations in an office setting can reduce worker productivity. Doing an acoustic analysis of the design has become a critical part of any design solution for most commercial building types. Newer acoustical products are designed to blend with other interior elements.

Isolating Sound

Sound can be transmitted through air as well as through the solid materials of a building's structure. Because structure-borne sounds are difficult to control, they should be isolated at their source whenever possible. Strategies include using quieter mechanical equipment, using resilient mountings and flexible connections to isolate equipment vibrations from the building structure, and eliminating flanking paths along interconnecting ductwork or piping that the noise can take from its source to the space.

Audio frequencies from 15 Hz to 16,000 Hz

Every material has acoustic implications, and any finish or object in a space can absorb, block, or transmit sound. Some furniture makers are creating product lines that use contemporary aesthetics to address noise reduction with acoustic space dividers and privacy pods. However, acoustic control with furnishings and panel systems, along with quieter HVAC systems like chilled beams, can sometimes make a space too quiet for comfort, where even quiet sounds are a disturbance.

Noise reduction refers to the perceived difference in sound levels between two enclosed spaces. Noise reduction depends on the following:

• The transmission loss through the wall, floor, and ceiling construction.
• The absorptive qualities of the receiving space.
• The level of masking or background sound, which can increase the threshold of audibility for other sounds in its presence.

Background or ambient sound from both exterior and interior sources is normally present in an environment. Background sound is not distinctly identifiable by the listener. A type of background sound called white noise is sometimes deliberately introduced into a space to mask or obliterate unwanted sound.

The required noise reduction from one space to another depends on the level of the sound source and the level of sound intrusion that may be acceptable to the listener.

Transmission loss (TL) is a measure of the performance of a building material or construction assembly in preventing the transmission of airborne sound. Three factors enhance the TL rating of a construction assembly:

• Mass: In general, the heavier and more dense a body, the greater is its resistance to sound transmission.
• Separation into layers: Introducing air spaces into the construction assembly disrupts the path through which sound may be transmitted from one space to another.
• Absorption: Absorptive materials help to dissipate sound in a room.

Acoustically absorptive materials

A sound transmission class (STC) rating is a single number that combines TL values from many frequencies. The STC provides an estimate of the performance of a partition in certain common sound insulation situations. The higher the STC rating, the greater is the sound-isolating value of the material or construction. An open doorway has an STC rating of 10; normal construction has STC ratings from 30 to 60; special construction is required for STC ratings above 60.

An example of commercially available acoustical panels

Staggering the studs of a wall or partition—forming two separate rows of studs arranged in a zigzag fashion—breaks the continuity of the path through which structure-borne sound can be transmitted.

Installing a fiberglass blanket in between the two rows of studs increases the transmission loss.

Mounting the finish material on resilient channels permits the surface to vibrate without transmitting noise to the supporting structure.

Sound can be transmitted through any clear air path, even the tiniest cracks around doors, windows, and electrical outlets. Careful sealing of these openings can prevent airborne noise from entering a room.

The sound-absorptive qualities of a material depend on its thickness, density, porosity, and resistance to airflow. Fibrous materials allow the passage of air while trapping sound energy, and are therefore often used in acoustic materials such as batts and blankets of fiberglass or mineral fiber.

In a normally constructed room without acoustical treatment, sound waves strike the wall, ceiling, and floor surfaces, which then transmit a small portion of the sound to adjacent spaces. The room surfaces absorb another small amount of the sound, but most of it is reflected back into the room.

Absorptive materials can dissipate some of the incident sound energy and reduce the portion of sound transmitted. This is particularly helpful in spaces with distributed noise sources, such as offices, schools, and restaurants.

Reducing reverberation from the ceiling plane is usually the most common approach to sound control in a room. Acoustical ceiling tiles are excellent absorbers of sound. They absorb more sound when mounted in a suspended ceiling system than when attached directly to a surface. Perforated metal ceiling panels with acoustic backing and acoustical ceiling panels made of bonded wood fibers also work well to control noise.

Treating walls and floors also helps to control sound. Acoustical wall panels can accomplish this, and may be made of felt or have fire-rated fabric coverings. Acoustical room dividers are becoming increasingly common, including ones designed as blinds that can open or close with a simple twist. Felt wall covering panels are also available for acoustical control.

Carpet is the only floor finish that absorbs sound. In addition, it can cushion footfalls and the sounds of furniture movement, thus limiting transmission of impact noise to the space below.

The average coefficient of absorption measures how efficiently materials in a room absorb sound; the lower the rating, the more sound is being absorbed.

The sound absorption average (SAA) is the average of sound absorption coefficients at a range of frequencies. Manufacturers list SAA ratings for acoustic products; some may use older noise reduction coefficient (NRC) ratings, which are similar.

Acoustical wall panels

Acoustic privacy continues to be a desired trait for office workers, as well as for those who telecommute. Material choices and room typologies affect the sound of a space, as well as employee health and comfort. Open-plan offices can have detrimental effects on acoustic privacy and speech intelligibility.

Office workstations or cubicles do not usually have full-height partitions, and noise can be a problem. Office cubicles often use acoustical material to absorb some of the sound, but sound often travels through cubicle openings and over the tops of low walls. Locating workstations carefully can help to block some of this sound.

A significant amount of the sound in offices is reflected off the ceiling. A suspended acoustical tile ceiling will absorb unwanted sound. Where an open ceiling is desired, acoustical clouds or canopies over noisy areas can help control sound levels. Combining ceiling and wall treatments with careful siting of furnishings helps to keep sounds from spreading.

The intrusiveness of overheard speech is related to its intelligibility. Electronic sound-masking systems can help to reduce the intelligibility of overheard speech by raising the ambient noise level of an otherwise quiet space. Emitting sound that is often compared to whooshing air, sound masking systems are engineered to block the frequencies of human speech, keeping a neighbor's conversations from distracting an individual from his or her task. Systems are available as networks of 3-inch speakers that are installed in the ceiling and project sound directly into the workspace. They are particularly desirable for unfinished or exposed ceilings.