Illumination is one of a number of modern energy services provided by electricity, a premium energy carrier with the advantage that it can be transmitted over large distances and converted on-demand at the point-of-use. Annual energy consumption in the United States is roughly 100 quadrillion Btu1 (quads) (Figure 1.1) (NRC, 2010b). Of this, roughly 40 percent is used to generate electricity, the vast majority of which is harnessed and sold to end users (3,750 TWh in 2010) in the residential (38.5 percent), commercial (35.4 percent), industrial (25.9 percent), and transportation (0.2 percent) sectors (EIA, 2011). General lighting for illumination consumes approximately 20 percent of the electricity used in the United States, accounting for between 7 to 19 percent of all residential electricity use and 31 to 36 percent of all commercial electricity use (Azevedo et al., 2009). Reducing energy consumption through conservation (i.e., using less of an energy service), improved thermodynamic efficiency, or greater efficacy (i.e., using less fuel) in delivering energy services (e.g., miles per gallon) has been the focus of a number of federal and state government programs of tax incentives, grants and contracts for research and development, standards (e.g., for appliances and vehicles), and building codes.2 The extraction of energy resources and their processing, conversion, delivery, and use can have negative impacts on human health and the environment (NRC, 2010a). To the extent such impacts scale with (i.e., are proportional to) the quantity of energy consumed, improving the efficiency of end-use of electricity can mitigate them. This makes improvements in end-use technologies a critical aspect of U.S. energy policies.
The standard incandescent light bulb, in wide use in the residential sector, still works mainly as Thomas Edison invented it, with more than 90 percent of the electricity consumed being converted to heat. The ability to dramatically decrease the energy used for lighting requires new technologies that use less power but are also affordable and capable of producing high-quality light. Given the availability of newer lighting technologies that convert a greater percentage of electricity into useful light, there is a lot of potential to decrease energy used (i.e., the amount of electricity) for lighting. Although technologies such as compact fluorescent lamps (CFLs) have emerged in the past few decades that will help achieve the goal of increased energy efficiency, solid-state lighting (SSL) stands to play a large role in dramatically decreasing our energy consumption for lighting.
Electricity end-use is part of a larger system, and it is instructive to consider the electricity grid and its overall efficiency. The power plants by which electricity is generated in the United States operate such that roughly two-thirds of the primary energy in the fuel is lost in electricity generation.3 Losses also occur in electricity transmission and distribution (6.5 percent), in which electricity is converted to heat, and finally when converting electricity to energy services such as illumination, space conditioning (i.e., heating, ventilation, and cooling), and cooking services (Figure 1.2).
Since the advent of the incandescent bulb, a number of new lighting technologies, discussed in detail below, have been demonstrated and in some cases entered widespread deployment to provide general and specialized illumination. A recent entrant is SSL. At the epicenter of SSL sits the semiconductor. In addition to using the semiconductor in electronic devices, scientists have been able to make the semiconductor emit light (Holonyak and Bevacqua, 1962). The most common semiconductor-based light source is the light-emitting diode (LED). If organic materials are used to fabricate the LED, it is called an organic LED (OLED). These two technologies are capable of creating “light bulbs”
1 Btu stands for British thermal unit and is a measure of energy. For instance, 1 gallon of gasoline would release approximately 124,000 Btu.
2 A review of such programs can be found in NRC (2010b, pp. 264-269).
3 The estimated two-thirds loss is based on using a single number for the so-called thermal efficiency of the fleet of power generators (called thermal because it is the amount of heat converted to useful work). There can be large variations among the different plants, however. Natural gas combined cycle plants can, for example, have efficiencies above 50 percent.
FIGURE 1.1 Total primary energy consumption in the United States, 2010 (in quadrillion Btu, or quads). Total U.S. primary energy use in 2010 was 98.0 quads.
or “lamps” that are much more efficient and have a much longer life span than either incandescent bulbs or compact fluorescent bulbs. LEDs and OLEDs alone cannot be used for illumination applications; additional electrical, thermal, structural, and optical components are necessary to create SSL products. Throughout the rest of the report, the term “SSL products” will be used to describe integrated LED or OLED lighting systems. In addition, LEDs and OLEDs are not limited to the current shape of existing lighting technologies and, therefore, have the potential to dramatically alter how we integrate light into our buildings and how our future “light bulbs” and luminaires might look and behave.
Congress recognized the potential for energy savings in the lighting sector in the Energy Independence and Security Act of 2007. Congress requested that the Department of Energy (DOE) contract with the National Research Council (NRC) to conduct a study to assess the status of SSL as a technology. The statement of task is separated into three main sections (Box 1.1): a review of the development of SSL technology and products, a discussion of future impacts, and the implications of the study for decision-making. The main tasks for the study were to investigate the following:
• Status of SSL research, development, demonstration, and commercialization in the United States;
• Timeline for commercialization of this technology as a replacement technology for current light sources;
• Past, current, and future cost trajectories for SSL;
• Consumer acceptance of and potential benefits from SSL;
• Potential barriers to success of the industry, both in research and development (R&D) and manufacturing and commercialization;
• International aspects of SSL;
• Applications for the technology, both current and future;
• Unintended consequences of SSL in different applications;
• Application of lessons learned from the commercialization of CFLs to the roll out of SSL; and
• Recommendations to DOE for research, development, and deployment activities.
FIGURE 1.2 Example of how end-use efficiency influences overall fuel conversion efficiency. In this example, typical for residential use of electricity for illumination, the efficiency of converting the chemical energy stored in coal to the electricity entering a building is about 33 percent (0.35 × 0.94). But after accounting for the low efficiency of the incandescent light bulb, the efficiency of converting chemical energy to light energy is only 1.3 percent. All values are approximate. SOURCE: Updated and adapted from National Research Council (2010b).
The National Research Council (NRC) will appoint a committee to carry out this study and provide a report on the status of advanced solid-state lighting (SSL), in particular light-emitting diodes and organic light-emitting diodes. The report will provide an assessment of the current status of development of SSL products, a discussion on the future impacts of SSL, and a consideration of the study’s implications for the U.S. Department of Energy (DOE) and other agencies. Specifically, the committee will focus on the following three overarching tasks.
(1) Review the Development ot SSL Technology and Products
The committee will assess:
• Past and current cost evaluations for SSL In relation to traditional lighting technologies;
• The status of SSL research, development, demonstration and commercialization in the US.;
• Potential barriers to development and the prospects for overcoming them;
• The status of SSL activities Internationally and thell Implications for the manufacturing of SSL technologies In the US;
• The cost, lifetime, reliability, and consumer satisfaction aSSOCiated with SSL for both Indoor and outdoor lighting appllCJtlons and how these factors compare to traditional lighting technologies (Incandescent, fluorescent, and high Intensity discharge);
• The market-based performance attributes necessary for SSL based on revi ew of on-going activities.
(2) Discussion ot SSL Future Impacts
The committee will estimate:
• The tl me line for the commerCialization of SSL (and other POSSI ble technologies) that could replace current I nCJndescent and halogen Incandescerlt lamp technology and meet the minimum standards requllej In Section 321 of the Energy Independence and Security Act of 2007;
• The barriers to widespread adoption of SSL technologies and strategies needed to overcome these barriers;
• The benefits for consumers If SSL development and deployment IS sucoessful and the I mpact If these barriers are not fully overcome, partlcu larly as It relates to the new minimum efficiency standard taking effect;
• Potential Unintended consequences of SSL deployment, such as presented by traffic lights uSing SSL lamps that did not generate enough heat to melt Ice that bUilt up on them.
(3) Study Implicalions
The committee will analyze:
• Lessons from the experience with the commerCialIZation of compact fluorescent lighting and how that may affect potential proactive Initiatives by the Department of Energy and other agencies (with legislative dllectlon, such as the Federal Trade Commission (FTCI); and
• Recommendations to the Department of Energy on research, development, and deployment activities, and potential collaborations with market partiCipants, espeCially manufacturers.
The committee will provide a report to the U.S. Department of Energy, the Committee on Energy and Commerce of the House of Representatives, and the Committee on Energy and Natural Resources of the Senate. As mandated by Energy Independence and Security Act of 2007, the NRC could also provide an updated report by July 31, 2015.
With these tasks in mind, the NRC established the Committee on Assessment of Solid State Lighting (Appendix A) composed of diverse experts in the fields of solid-state lighting, lighting design, human perception of light, industry commercialization, and policy to address the statement of task. In conducting this study, the committee members relied on their own expertise as well as many interactions with experts in the field (Appendix B).
Americans are used to purchasing their lamps (i.e., light bulbs) as a function of the rating in watts (and “watt equivalents”), a unit denoting the rate at which energy is produced or consumed. Intuitively, most people understand how much light a 40 W incandescent lamp provides compared to a 60 W or 75 W lamp. As the technological options for lighting shift
away from the incandescent lamp to more energy efficient alternatives such as CFLs and solid-state options (LEDs and OLEDs), the basic terms used for lighting discussions also need to change. Instead of thinking in terms of watts, consumers now need to learn a different measurement system, one that tells them how much light a product is going to emit (in absolute terms or per unit of power consumed) instead of the rate at which energy will be consumed. And this is just the beginning of the changes that consumers are likely to see if LED and OLED lighting continue to improve at their current rates. In this section, several key concepts and terms used in the lighting industry are introduced that will be used throughout the rest of the report.
Lighting designers and engineers use different terms for lighting equipment than are used in the vernacular. In this report, the engineering terms will be used. A luminaire is the combination of light fixture hardware, a ballast or driver if applicable, and a light source, commonly called a lamp (i.e., a light bulb). Thus, the term lamp can refer to an incandescent bulb, a CFL bulb, or an LED replacement “bulb.” This report will use the term lamp. A luminaire consists of, minimally, a lamp holder, commonly called a socket, and the way to connect the socket to the electrical supply. Most fixtures also contain optical elements that distribute the light as desired, such as a reflector, lens, shade, or globe. When needed, fixtures and luminaires contain a ballast or a driver. A ballast is an electronic device that converts incoming electricity to the proper voltage and current required to start and maintain the operation of a lamp. The term driver refers to the corresponding device used in an SSL luminaire. Luminaire examples include chandeliers, downlights, table lamps, wall sconces, recessed or pendant mounted luminaires, and exterior streetlights. When equipped with lamps, they are called luminaires. The types of lamps typically encountered are discussed below in the section “Annex.”
The portion of the electromagnetic spectrum that can be perceived by the human visual system is called the visible spectrum. The amount of light, weighted by the sensitivity of the visual system, emitted by a source per unit time is its luminous flux (Figure 1.3) and is measured in lumens (lm). This makes lumens one of the appropriate pieces of information for lamp packaging to help consumers choose the appropriate replacement lamps. Lumens provide a description most closely related to brightness and should be referred to when choosing replacement lamps. A proliferation of fact sheets and labels has accompanied the recent introduction of new lighting technologies, leaving some consumers confused about the relationship between watts and lumens. That relationship is determined by the energy efficiency of the product. Watts describe the amount of electrical power consumed by the product, and lumens describe the rate at which it emits light. For example, most 60 W incandescent lamps emit approximately 850 lumens. Similarly, many 13 W CFLs emit 850 lumens.
FIGURE 1.3 Luminous flux (lumena).
FIGURE 1.4 Luminous intensity (candela).
Luminous intensity (Figure 1.4) is the luminous flux per unit solid angle, evaluated in terms of a standardized visual response and expressed in candela. The magnitude of luminous intensity results from luminous flux being redirected by a reflector or magnified by a lens.4 This measurement is used primarily to describe the specific light intensity and
4 The concept of solid angle has a strict geometric definition but can be thought of as a way to describe the focusing and redirecting of a light source by the lenses and reflectors in the luminaire.
distribution of a luminaire. Illuminance is the concentration of luminous flux incident on a surface (Figure 1.5). The unit of illuminance is lux (lx), and it indicates the number of lumens per square meter. Lumens per square foot are called footcandles (ftc). Whereas luminous flux relates to the total output of a lamp or lighting product, illuminance relates to the amount of light striking a surface or point. Illuminance depends on the luminous flux of the light sources and their distances from the illuminated surface.
Luminance is a measure used for self-luminous or reflective surfaces (Figure 1.6). It expresses the amount of light, weighted by the sensitivity of the visual system, per unit area of the surface that is travelling in a given direction and is expressed as candelas per square meter (cd/m2). When referring to illuminated surfaces, luminance is determined by the incident light (illuminance) and the reflectance characteristics of the surface. For instance, light- and dark-colored walls will have different luminance values when they have the same illuminance. Luminance is a metric used for internally illuminated variable-sized flat light sources forms, such as sheets or tapes, because the total luminous flux will depend on the surface area of the product.
FIGURE 1.5 Illuminance (lux). The amount of light striking a surface or point, measured in lux (lx).
FIGURE 1.6 Luminance of a luminaire.
The luminous efficacy of a lighting product is the ratio of the luminous flux to the total electrical power consumed and has units of lumens per watt (lm/W). A perfect light source— that is, one that converts all the electricity into visible light— would have an efficacy of 408 lm/W for an assumed color rendering index (CRI; a measure of color quality, discussed below) of 90 (Phillips et al., 2007).5 The luminous efficacy of a typical 60 W incandescent lamp (luminous flux of 850 lumens) is such that only 14.2 lumens are emitted per watt of power drawn by the light bulb. As efficacies increase, more of the power is used to generate visible light, and this leads to a more efficient product. High color quality LEDs currently are being manufactured with efficacies in the range of 60 to 188 lm/W. It should be borne in mind that efficacy is different from efficiency. The efficiency of a lighting system is the ratio between the obtained efficacy and the theoretical maximum efficacy of a light source (408 lm/W for a CRI of 90) and is always expressed as a percentage. Thus, it accounts for the ballast efficiency (if there is one), the light source efficacy, and the luminaire efficiency (see Figure 1.7) in one lumped parameter. Thus, incandescent lamps with system efficacies ranging from 4 to 18 lm/W (depending largely on the wattage of the bulb) will have system efficiencies of only about 0.2 to 2.6 percent. Efficiency does not, however, account for the perceived quality of the light. Using the theoretical maximum of 408 lm/W and the ranges of efficacies for different lighting technologies leads to the ranges of system efficiencies shown in Figures 1.7 and 1.8.
The human eye can generally detect light with wavelengths between 380 nm (corresponding to blue/violet light) and 750 nm (corresponding to red light). The spectral power distribution (SPD) determines several important properties of a light source. The SPD describes the relative amount of light per wavelength per unit time emitted by a light source and is often graphically represented, as shown in Figure 1.9. Figure 1.9 shows the SPDs of a halogen lamp, a red, green, blue (RGB) LED (which produces white light by combining red, green, and blue component LEDs), an OLED, and a combination of four colored lasers.
The color of emitted light as perceived by people, called chromaticity, is regulated by the spectral composition. The human visual system does not process light on a wavelength-by-wavelength basis. Instead, the brain receives signals from only three input channels, the different cone photopigments found in the eye. Because of this, countless different SPDs can produce light identical in chromaticity. To illustrate this,
5 A different choice of color rendering index = 80 would lead to a maximum efficacy of 423 lm/W, and so forth.
FIGURE 1.7 Efficacy of lamps and luminaires. Values in the left-most column report the range of efficiencies for ballasts and electronic drivers. Values in the central column report efficacies for different lighting devices. The values on the third column report ranges of luminaire efficiencies. The values on the right-most column report the overall system efficacies of the luminaire. SOURCE: Adapted from Azevedo et al. (2009), where the efficacies for white LEDs were updated to reflect currently commercialized warm and cool white LEDs. NOTE: AC = alternating current; HID = high-intensity discharge; Hz = Hertz; LED = light-emitting diode.
FIGURE 1.8 Overall efficiencies of lighting systems (lower bounds) and devices (upper bounds) when assuming that the theoretical maximum lamp efficacy is 408 lm/W; LED = light-emitting diodes; HID = high-intensity-discharge lamps; CFL = compact fluorescent lamps. Lower and upper bounds correspond to the low- and high-efficacy values shown in Figure 1.7. SOURCE: Azevedo et al. (2009).
the four widely varying SPDs shown in Figure 1.9 would all produce light that would appear indistinguishable.
On the correlated color temperature (CCT) scale, all four spectra lights in Figure 1.9 are approximately 3,000 K. Correlated color temperature is used to describe nominally white light sources and refers to the temperature of a blackbody radiator that produces a light perceived to be most similar in chromaticity to the white light source. A typical incandescent lamp has a CCT of 2,500 kelvin (K) to 3,000 K, whereas office and school lighting is often 4,000 K
FIGURE 1.9 Spectral power distribution from very different light sources that were chosen to produce identically appearing white light. The red, green, blue (RGB) light-emitting diode (LED) produces white light by combining red, green, and blue component LEDs, as does a combination of four colored lasers.
to 5,000 K. Lower CCTs include more light nearer the red end of the visible spectrum and are perceived to be “warmer,” while higher CCTs tend toward the blue end and are perceived to be “cool.” In somewhat of a misnomer, the labeling is indicative of the feelings they evoke rather than their actual temperatures. Although the color of daylight changes throughout the day and with location on Earth, it is commonly described as having a CCT of 6,500 K. Although CCT is widely used among lighting manufacturers and designers, it only describes one dimension of light source chromaticity, in the blue-yellow direction. It does not consider pink-green shifts in white light color, although Duv is a measure increasingly used for that information.
The most common system for specifying and communicating the precise chromaticity of light sources uses CIE 1931 (x,y) chromaticity coordinates (CIE, 2004). The CIE 1931 (x,y) chromaticity diagram is shown in Figure 1.10. The curved edge of the outer horseshoe shape on the diagram is the spectrum locus and is comprised of the colors of monochromatic (only one wavelength) radiation. The straight edge line is the purple line, and the colors are always a combination of red and blue (not monochromatic).
Chromaticity does not provide all of the color information of interest for general illumination applications. The color of the light itself does not predict the appearance of colored objects illuminated by the source, a property referred to as color rendering. Although color rendering is determined by the spectral output of a light source, it cannot be predicted by a cursory inspection of the shape of the spectral power distribution, and subtle differences in SPD can produce marked differences in the chromaticity of illuminated objects (Ohno, 2005).
The SPD also determines the LER (i.e., the luminous efficacy of radiation) of a light source. In technical terms, LER is the ratio of luminous flux to radiant flux.6 In simple terms, the LER is luminous efficacy that could be achieved if the light source was able to convert electricity to light perfectly with no losses. The final luminous efficacy of a light source is determined from both the LER and the efficiency with which the technology converts electricity to light. The sensitivity of the human visual system differs for the various wavelengths in the visible range. The relationship between wavelength and the relative sensitivity of the human visual system is described by the spectral luminous efficiency function (Vλ) (CIE, 1926) which is shown by the dashed curves in Figure 1.11. This function peaks at 555 nm. Light of this wavelength has a LER of 683 lm/W, setting the upper bound
6 Radiant flux is the amount of electromagnetic energy emitted per unit time at all wavelengths including visible light and other spectral bands. As such it will exceed the luminous flux.
FIGURE 1.10 CIE 1931 (x,y) chromaticity diagram. Numbers indicate wavelength of light, in nanometers. SOURCE: Wikipedia Commons.
for luminous efficacy, as illustrated by the 555 nm laser in panel a. It is important to note that white light cannot achieve 683 lm/W, only light at 555 nm can. Visual sensitivity is markedly lower for light in the short- and long-wavelength regions of the visible spectrum. The other three panels of Figure 1.11 show different SPDs and their corresponding LER. Panel b shows an RGB white LED, panel c shows a different type of white LED (called a phosphor LED, to be discussed later), and panel d shows the SPD of a typical incandescent lamp. As shown, the effect of spectral power distribution on luminous efficacy can be substantial. The incandescent SPD has a relatively low LER because it has a lot of energy in the very long visible and infrared wavelengths, to which the visual system is either minimally or completely insensitive.
Although the wavelengths of light to which the eye is most sensitive lie in the middle of the spectrum, a light source composed of light only in the middle of the visible spectrum would not be useful for general illumination. To achieve desirable color characteristics, light of other wavelengths must be present. There is generally a trade-off between luminous efficacy and color quality (Ohno, 2005). Depending on the application and goals of a lighting product or lit environment, a luminaire manufacturer or lighting designer may choose to prioritize one trait over the other. For example,
FIGURE 1.11 Spectral power distribution determines luminous efficacy of radiation (LER). The dashed green curves show the Spectral Luminous Efficiency Function and the black curves are light source’s spectral power distributions. NOTE: RGB = red, green, blue.
in a parking garage with lights on 24 hours a day, a specifier may require excellent efficacy and accept subpar color quality. On the other hand, a museum may require superior color and be willing to sacrifice efficacy.
Good color rendering can be achieved with such discontinuous light spectra because of the properties of the other two elements in the process of perceiving object colors: the reflectance of the objects and the absorption of the cone photopigments in the human visual system. All objects, natural or artificial, reflect as a function of wavelength in a very broad and continuous manner. The reflectance factors of these objects (the proportion of light reflected as a function of wavelength) do not show sudden spikes or isolated dips in reflectivity across the visible spectrum. Because of this, the general shape of the reflectance factor can be interpolated with fairly coarse wavelength sampling. The three cone photopigments responsible for color vision have absorption functions that are very broad, continuous, and overlapping in wavelength sensitivity. Each cone type responds to many wavelengths, although sensitivity does change depending on the wavelength. The outputs of these photoreceptors do not signal the wavelength composition of the stimulus to the brain. For instance, a certain level of activity from one cone type could result from a small amount of energy at every wavelength it is sensitive to or a lot of energy at only one wavelength it is sensitive to. The visual system makes absolutely no distinction between these two situations (Rushton, 1972). The perception of color arises from combining and comparing the activity among the three cone types. Therefore, countless combinations of input wavelengths can lead to the exact same perception of color. These circumstances, in which objects reflect in a fairly predictable manner and the visual system interprets incoming light in terms of three broadly sensitive channels, allow a great deal of flexibility for the spectral content of light sources. A recent study demonstrated an extreme case of this in which light sources were developed composed of only four lasers (i.e., sources with extremely narrow emission spectra) with high color rendering quality (Neumann et al., 2011).
FINDING: A light source need not emit energy at every visible wavelength in order to achieve high color quality (Figure 1.9). An understanding of the spectral power distribution’s effects on luminous efficacy and the color properties of a light source will enable SSL developers to optimize energy efficiency while maintaining good color quality.
At the beginning of this chapter, we briefly described the U.S. electricity use by sector. Concerning the contribution of lighting to overall electricity consumption, it is generally agreed that nearly 20 percent of U.S electricity generation is used in lighting (Azevedo et al., 2009). However, there are no detailed time-series data, and there is a large uncertainty regarding actual lighting electricity consumption. The recent lighting market characterization for 2010 from DOE (2012) estimates that electricity consumption for lighting in the residential, commercial, industrial, and outdoor stationary sectors is 175 terawatt hours (TWh), 349 TWh, 58 TWh, and 118 TWh, respectively, thus totaling 700 TWh for all sectors. Another recent estimate, from the Energy Information Administration (EIA, 2011), suggests that in 2010 the residential and commercial sectors used about 499 TWh of electricity for lighting, which corresponds to roughly 18 percent of the total electricity consumed by both of those sectors.7 The most recent (2006) EIA data available for the manufacturing sector show 63 TWh consumed in lighting, which corresponds to 7 percent of all electricity consumed by manufacturing and 2 percent of all electricity used by the United States (EIA, 2009).
DOE (2012) reports a breakdown by technology type for each sector, estimating that in the commercial sector linear fluorescent lamps are responsible for 72 percent of lighting electricity consumption, and that the residential sector is still dominated by incandescent lamps (accounting for 78 percent of residential lighting electricity consumption). In 2010, incandescent lamps accounted for 45 percent of lamps for all sectors in the United States. Linear fluorescent lamps and CFLs together now account for a larger share in terms of number of lamps (48 percent), while LEDs account for 0.8 percent. In terms of shipments, the Buildings Energy Data Book (DOE, 2011) estimates that ENERGY STAR® lamps8 were 15 percent of total shipments of medium screw-based lamps in 2009. Overall, there is a lack of data on annual market characterization, which are crucial to understand the impact of current and future policies.
Chapter 2 provides an in-depth look at the suite of instruments—R&D investments, standards, demonstration projects, and so forth—by which governments have stimulated more efficient use of energy for illumination. The chapter also includes a case-study of early-generation CFLs in order to extract lessons applicable to the introduction of SSL products in the market. Chapter 3 discusses the two candidate technologies for manufacture of SSL products— LEDs and OLEDs—and evaluates the barriers remaining to widespread deployment in luminaires, including challenges in research, development, and manufacturing. Included as well is a primer on each technology. Chapter 4 focuses on the luminaires themselves and the challenges to their assembly
7 EIA reports that it does not have an estimate for only public street and highway lighting, but these applications are considered part of the commercial sector in the EIA report and are thus included in the 499 TWh.
and integration into buildings and electricity systems. Chapter 5 provides a perspective on the design and installation of LED and OLED luminaires. Chapter 6 discusses the market barriers to the adoption of SSL products.
There are many different kinds of lamps. Most of the lamps used in residential applications are omnidirectional (emit light in all directions) incandescent lamps, typically with a medium screw base (Figure 1.12) that fits into most residential luminaires. In addition, there are candelabra and intermediate base lamps that are commonly used in residential applications, especially in chandeliers and wall sconces. Incandescent lamps produce light by heating a tungsten filament to a temperature of approximately 2,500 K to 3,000 K where the filament glows or incandesces.
Halogen lamps are incandescent lamps in which the tungsten filament has been enclosed in a capsule containing a halogen gas, typically bromine, which allows the filament to operate at a slightly higher temperature without reducing the rated life and resulting in a somewhat higher light output than the standard incandescent lamp. Halogen lamps are available that emit light omnidirectionally, as well as directional varieties, often known as reflector lamps. Reflector lamps are designated by the properties of their reflectors, such as PAR (parabolic aluminized reflector (Figure 1.13) or MR (multifaceted mirror reflector), and are most commonly either standard incandescent or halogen. The low-voltage MR-16 lamp (Figure 1.14) commonly used in accent, task, and display lighting uses halogen technology.
FIGURE 1.12 Incandescent with medium screwbase (A-19).
Fluorescent lamps are available in a range of shapes and sizes. Linear fluorescent lamps are frequently used in commercial spaces (offices, stores) and are typically long 4-foot tubes. They are often installed in recessed luminaires in the ceiling or are pendant-mounted from the ceiling. All fluorescent lamps require a ballast. CFLs are available with screw bases and an integral ballast (Figure 1.15) for use as replacements for incandescent lamps or with pin bases for use with a separate ballast (Figure 1.16). Both CFLs and linear fluorescent lamps produce light by exciting phosphors, which then fluoresce, with ultraviolet energy. A small amount of mercury is added to the lamp to emit ultraviolet light at a suitable wavelength for exciting the phosphor.
High-intensity-discharge (HID) lamps are electric lamps with tubes filled with gas and metal salts. The gas initiates an arc, which evaporates the metal salts, forming a plasma. This results in an efficient and high-intensity light source. These lamps are suitable for both indoor and outdoor applications and are generally used to light large spaces or roadways. All HID lamps require a ballast.
Mercury vapor, metal halide (Figure 1.17), and high-pressure sodium lamps are examples of specific types of HID lamps. HID lamps require a warm-up period to reach stable output as well as a cool-down period before restarting.
FIGURE 1.13 PAR 20 lamp (tungsten halogen).
FIGURE 1.14 MR 16 lamp (tungsten halogen).
FIGURE 1.15 Compact fluorescent lamp (screw base with integral ballast).
FIGURE 1.16 Fluorescent lamp (T5) without integral ballast.
FIGURE 1.17 Metal halide lamp (an example of high-intensity discharge lamp).
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