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1
Introduction
CONTEXT decrease the energy used for lighting requires new technolo-
gies that use less power but are also affordable and capable
Illumination is one of a number of modern energy services
of producing high-quality light. Given the availability of
provided by electricity, a premium energy carrier with the
newer lighting technologies that convert a greater percent-
advantage that it can be transmitted over large distances and
age of electricity into useful light, there is a lot of potential
converted on-demand at the point-of-use. Annual energy
to decrease energy used (i.e., the amount of electricity) for
consumption in the United States is roughly 100 quadrillion
lighting. Although technologies such as compact fluorescent
Btu1 (quads) (Figure 1.1) (NRC, 2010b). Of this, roughly
lamps (CFLs) have emerged in the past few decades that will
40 percent is used to generate electricity, the vast majority
help achieve the goal of increased energy efficiency, solid-
of which is harnessed and sold to end users (3,750 TWh in
state lighting (SSL) stands to play a large role in dramatically
2010) in the residential (38.5 percent), commercial (35.4 per-
decreasing our energy consumption for lighting.
cent), industrial (25.9 percent), and transportation (0.2 per-
Electricity end-use is part of a larger system, and it is
cent) sectors (EIA, 2011). General lighting for illumination
instructive to consider the electricity grid and its overall effi-
consumes approximately 20 percent of the electricity used
ciency. The power plants by which electricity is generated in
in the United States, accounting for between 7 to 19 percent
the United States operate such that roughly two-thirds of the
of all residential electricity use and 31 to 36 percent of all
primary energy in the fuel is lost in electricity generation.3
commercial electricity use (Azevedo et al., 2009). Reducing
Losses also occur in electricity transmission and distribution
energy consumption through conservation (i.e., using less of
(6.5 percent), in which electricity is converted to heat, and
an energy service), improved thermodynamic efficiency, or
finally when converting electricity to energy services such
greater efficacy (i.e., using less fuel) in delivering energy ser-
as illumination, space conditioning (i.e., heating, ventilation,
vices (e.g., miles per gallon) has been the focus of a number
and cooling), and cooking services (Figure 1.2).
of federal and state government programs of tax incentives,
Since the advent of the incandescent bulb, a number of
grants and contracts for research and development, standards
new lighting technologies, discussed in detail below, have
(e.g., for appliances and vehicles), and building codes.2 The
been demonstrated and in some cases entered widespread
extraction of energy resources and their processing, conver-
deployment to provide general and specialized illumina-
sion, delivery, and use can have negative impacts on human
tion. A recent entrant is SSL. At the epicenter of SSL sits
health and the environment (NRC, 2010a). To the extent such
the semiconductor. In addition to using the semiconductor
impacts scale with (i.e., are proportional to) the quantity of
in electronic devices, scientists have been able to make the
energy consumed, improving the efficiency of end-use of
semiconductor emit light (Holonyak and Bevacqua, 1962).
electricity can mitigate them. This makes improvements in
The most common semiconductor-based light source is the
end-use technologies a critical aspect of U.S. energy policies.
light-emitting diode (LED). If organic materials are used
The standard incandescent light bulb, in wide use in the
to fabricate the LED, it is called an organic LED (OLED).
residential sector, still works mainly as Thomas Edison
These two technologies are capable of creating “light bulbs”
invented it, with more than 90 percent of the electricity con-
sumed being converted to heat. The ability to dramatically 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
1 Btu stands for British thermal unit and is a measure of energy. For because it is the amount of heat converted to useful work). There can be large
instance, 1 gallon of gasoline would release approximately 124,000 Btu. variations among the different plants, however. Natural gas combined cycle
2 A review of such programs can be found in NRC (2010b, pp. 264-269). plants can, for example, have efficiencies above 50 percent.
6
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INTRODUCTION 7
Industry
Transportation STUDY ORIGIN
28%
31% Congress recognized the potential for energy savings in
(28 quads)
(30 quads) 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
Commercial tasks for the study were to investigate the following:
Residential
Buildings
Buildings
19% • Status of SSL research, development, demonstration,
23%
(18 quads) and commercialization in the United States;
(22 quads)
• Timeline for commercialization of this technology as
FIGURE 1.1 Total primary energy consumption in the United a replacement technology for current light sources;
States, 2010 (in quadrillion Btu, or quads). Total U.S. primary • Past, current, and future cost trajectories for SSL;
energy use in 2010 was 98.0 quads. • Consumer acceptance of and potential benefits from
1.01.eps SSL;
• Potential barriers to success of the industry, both in
research and development (R&D) and manufacturing
or “lamps” that are much more efficient and have a much
and commercialization;
longer life span than either incandescent bulbs or compact
• International aspects of SSL;
fluorescent bulbs. LEDs and OLEDs alone cannot be used
• Applications for the technology, both current and
for illumination applications; additional electrical, thermal,
future;
structural, and optical components are necessary to create
• Unintended consequences of SSL in different
SSL products. Throughout the rest of the report, the term
applications;
“SSL products” will be used to describe integrated LED or
• Application of lessons learned from the commercial-
OLED lighting systems. In addition, LEDs and OLEDs are
ization of CFLs to the roll out of SSL; and
not limited to the current shape of existing lighting technolo-
• Recommendations to DOE for research, develop-
gies and, therefore, have the potential to dramatically alter
ment, and deployment activities.
how we integrate light into our buildings and how our future
“light bulbs” and luminaires might look and behave.
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).
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8 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING
BOX 1.1
Statement of Task
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 of SSL Technology and Products
The committee will assess:
• ast and current cost evaluations for SSL in relation to traditional lighting technologies;
P
• he status of SSL research, development, demonstration and commercialization in the U.S.;
T
• otential barriers to development and the prospects for overcoming them;
P
• he status of SSL activities internationally and their implications for the manufacturing of SSL technologies in the U.S.;
T
• he cost, lifetime, reliability, and consumer satisfaction associated with SSL for both indoor and outdoor lighting applications and how these
T
factors compare to traditional lighting technologies (incandescent, fluorescent, and high intensity discharge);
• he market-based performance attributes necessary for SSL based on review of on-going activities.
T
(2) Discussion of SSL Future Impacts
The committee will estimate:
• he time line for the commercialization of SSL (and other possible technologies) that could replace current incandescent and halogen incandescent
T
lamp technology and meet the minimum standards required in Section 321 of the Energy Independence and Security Act of 2007;
• he barriers to widespread adoption of SSL technologies and strategies needed to overcome these barriers;
T
• he benefits for consumers if SSL development and deployment is successful and the impact if these barriers are not fully overcome, particularly
T
as it relates to the new minimum efficiency standard taking effect;
• otential unintended consequences of SSL deployment, such as presented by traffic lights using SSL lamps that did not generate enough heat
P
to melt ice that built up on them.
(3) Study Implications
The committee will analyze:
• essons from the experience with the commercialization of compact fluorescent lighting and how that may affect potential proactive initiatives
L
by the Department of Energy and other agencies (with legislative direction, such as the Federal Trade Commission [FTC]); and
• ecommendations to the Department of Energy on research, development, and deployment activities, and potential collaborations with market
R
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 Com- INTRODUCTION TO LIGHTING
mittee on Assessment of Solid State Lighting (Appendix A)
Americans are used to purchasing their lamps (i.e., light
composed of diverse experts in the fields of solid-state light-
bulbs) as a function of the rating in watts (and “watt equiva-
ing, lighting design, human perception of light, industry
lents”), a unit denoting the rate at which energy is produced
commercialization, and policy to address the statement of
or consumed. Intuitively, most people understand how much
task. In conducting this study, the committee members relied
light a 40 W incandescent lamp provides compared to a 60 W
on their own expertise as well as many interactions with
or 75 W lamp. As the technological options for lighting shift
experts in the field (Appendix B).
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INTRODUCTION 9
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, con-
sumers 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 Equipment
Lighting designers and engineers use different terms for LUMINOUS FLUX (lumens)
lighting equipment than are used in the vernacular. In this
FIGURE 1.3 Luminous flux (lumena).
report, the engineering terms will be used. A luminaire is 1.03.eps
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 incan-
descent 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. Lumi-
naire examples include chandeliers, downlights, table lamps, LUMINOUS INTENSITY (candela)
wall sconces, recessed or pendant mounted luminaires, and
exterior streetlights. When equipped with lamps, they are 1.04.eps
FIGURE 1.4 Luminous intensity (candela).
called luminaires. The types of lamps typically encountered
are discussed below in the section “Annex.”
Metrics for Measuring Light Output
the product. Watts describe the amount of electrical power
The portion of the electromagnetic spectrum that can be
consumed by the product, and lumens describe the rate at
perceived by the human visual system is called the visible
which it emits light. For example, most 60 W incandescent
spectrum. The amount of light, weighted by the sensitivity
lamps emit approximately 850 lumens. Similarly, many 13 W
of the visual system, emitted by a source per unit time is its
CFLs emit 850 lumens.
luminous flux (Figure 1.3) and is measured in lumens (lm).
Luminous intensity (Figure 1.4) is the luminous flux per
This makes lumens one of the appropriate pieces of infor-
unit solid angle, evaluated in terms of a standardized visual
mation for lamp packaging to help consumers choose the
response and expressed in candela. The magnitude of lumi-
appropriate replacement lamps. Lumens provide a descrip-
nous intensity results from luminous flux being redirected
tion most closely related to brightness and should be referred
by a reflector or magnified by a lens.4 This measurement
to when choosing replacement lamps. A proliferation of
is used primarily to describe the specific light intensity and
fact sheets and labels has accompanied the recent introduc-
tion of new lighting technologies, leaving some consumers
4 The concept of solid angle has a strict geometric definition but can be
confused about the relationship between watts and lumens.
thought of as a way to describe the focusing and redirecting of a light source
That relationship is determined by the energy efficiency of by the lenses and reflectors in the luminaire.
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10 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING
distribution of a luminaire. Illuminance is the concentration illuminated variable-sized flat light sources forms, such as
of luminous flux incident on a surface (Figure 1.5). The unit sheets or tapes, because the total luminous flux will depend
of illuminance is lux (lx), and it indicates the number of on the surface area of the product.
lumens per square meter. Lumens per square foot are called The luminous efficacy of a lighting product is the ratio of
footcandles (ftc). Whereas luminous flux relates to the total the luminous flux to the total electrical power consumed and
output of a lamp or lighting product, illuminance relates to has units of lumens per watt (lm/W). A perfect light source—
the amount of light striking a surface or point. Illuminance that is, one that converts all the electricity into visible light—
depends on the luminous flux of the light sources and their would have an efficacy of 408 lm/W for an assumed color
distances from the illuminated surface. rendering index (CRI; a measure of color quality, discussed
Luminance is a measure used for self-luminous or reflec- below) of 90 (Phillips et al., 2007).5 The luminous efficacy
tive surfaces (Figure 1.6). It expresses the amount of light, of a typical 60 W incandescent lamp (luminous flux of
weighted by the sensitivity of the visual system, per unit area 850 lumens) is such that only 14.2 lumens are emitted per
of the surface that is travelling in a given direction and is watt of power drawn by the light bulb. As efficacies increase,
expressed as candelas per square meter (cd/m2). When refer- more of the power is used to generate visible light, and this
ring to illuminated surfaces, luminance is determined by the leads to a more efficient product. High color quality LEDs
incident light (illuminance) and the reflectance characteris- currently are being manufactured with efficacies in the range
tics of the surface. For instance, light- and dark-colored walls of 60 to 188 lm/W. It should be borne in mind that efficacy is
will have different luminance values when they have the different from efficiency. The efficiency of a lighting system
same illuminance. Luminance is a metric used for internally 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 OBSERVER source efficacy, and the luminaire efficiency (see Figure 1.7)
in one lumped parameter. Thus, incandescent lamps with sys-
tem 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 theo-
retical 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.
VISIBLE SPECTRUM AND QUALITY OF LIGHT
The human eye can generally detect light with wave-
lengths between 380 nm (corresponding to blue/violet light)
ILLUMINANCE (lux)
and 750 nm (corresponding to red light). The spectral power
FIGURE 1.5 Illuminance (lux). The amount of light striking a distribution (SPD) determines several important properties
surface or point, measured in lux (lx). of a light source. The SPD describes the relative amount of
1.05.eps 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,
SOURCE OBSERVER blue (RGB) LED (which produces white light by combin-
ing red, green, and blue component LEDs), an OLED, and a
combination of four colored lasers.
LUMINANCE 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,
5A different choice of color rendering index = 80 would lead to a maxi-
FIGURE 1.6 Luminance of a luminaire.
mum efficacy of 423 lm/W, and so forth.
1.06.eps
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INTRODUCTION 11
Luminaire Efficacy of
Ballast efficiency Lamp efficacy efficiency luminaire
2 to 16 lm/W
(no ballast) Incandescent
40% to 90%
4 to 18 lm/W
6 to 30 lm/W
(no ballast) Halogen
15 to 33 lm/W 40% to 90%
Fluorescent 16 to 90 lm/W
60Hz AC 65% to 95% tubes 40% to 90%
60 to 105 lm/W
9 to 68 lm/W
65% to 95% CFL 40% to 90%
35 to 80 lm/W
4 to 120 lm/W
70% to 95% HID 40% to 90%
14 to 140 lm/W
18 to 170 lm/W
75% to 95% 40% to 95%
White LED
60 to 188 lm/W
FIGURE 1.7 Efficacy of lamps and luminaires. Values in the left-most column report the range of efficiencies for ballasts and electronic
1.07.eps
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
7 bitmaps with vector type & rules
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 white light sources and refers to the temperature of a black-
produce light that would appear indistinguishable. body radiator that produces a light perceived to be most
On the correlated color temperature (CCT) scale, all similar in chromaticity to the white light source. A typi-
four spectra lights in Figure 1.9 are approximately 3,000 K. cal incandescent lamp has a CCT of 2,500 kelvin (K) to
C
orrelated color temperature is used to describe nominally 3,000 K, whereas office and school lighting is often 4,000 K
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12 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING
Halogen RGB LED
Lasers
OLED
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. 1.09.eps
4 bitmaps with vector labels
to 5,000 K. Lower CCTs include more light nearer the red objects illuminated by the source, a property referred to as
end of the visible spectrum and are perceived to be “warmer,” color rendering. Although color rendering is determined by the
while higher CCTs tend toward the blue end and are per- spectral output of a light source, it cannot be predicted by a
ceived to be “cool.” In somewhat of a misnomer, the label- cursory inspection of the shape of the spectral power distribu-
ing is indicative of the feelings they evoke rather than their tion, and subtle differences in SPD can produce marked differ-
actual temperatures. Although the color of daylight changes ences in the chromaticity of illuminated objects (Ohno, 2005).
throughout the day and with location on Earth, it is com- The SPD also determines the LER (i.e., the luminous
monly described as having a CCT of 6,500 K. Although CCT efficacy of radiation) of a light source. In technical terms,
is widely used among lighting manufacturers and designers, LER is the ratio of luminous flux to radiant flux.6 In simple
it only describes one dimension of light source chromaticity, terms, the LER is luminous efficacy that could be achieved
in the blue-yellow direction. It does not consider pink-green if the light source was able to convert electricity to light per-
shifts in white light color, although Duv is a measure increas- fectly with no losses. The final luminous efficacy of a light
ingly used for that information. source is determined from both the LER and the efficiency
The most common system for specifying and com- with which the technology converts electricity to light. The
municating the precise chromaticity of light sources sensitivity of the human visual system differs for the various
uses CIE 1931 (x,y) chromaticity coordinates (CIE, 2004). wavelengths in the visible range. The relationship between
The CIE 1931 (x,y) chromaticity diagram is shown in wavelength and the relative sensitivity of the human visual
Figure 1.10. The curved edge of the outer horseshoe shape system is described by the spectral luminous efficiency func-
on the diagram is the spectrum locus and is comprised of the tion (Vλ) (CIE, 1926) which is shown by the dashed curves
colors of monochromatic (only one wavelength) radiation. in Figure 1.11. This function peaks at 555 nm. Light of this
The straight edge line is the purple line, and the colors are wavelength has a LER of 683 lm/W, setting the upper bound
always a combination of red and blue (not monochromatic).
Chromaticity does not provide all of the color information
6 Radiant flux is the amount of electromagnetic energy emitted per unit
of interest for general illumination applications. The color
time at all wavelengths including visible light and other spectral bands. As
of the light itself does not predict the appearance of colored such it will exceed the luminous flux.
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INTRODUCTION 13
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 Fig-
ure 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). Depend-
FIGURE 1.10 CIE 1931 (x,y) chromaticity diagram. Numbers ing on the application and goals of a lighting product or lit
indicate wavelength of light, in nanometers. SOURCE: Wikipedia environment, a luminaire manufacturer or lighting designer
Commons. 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.
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14 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING
in a parking garage with lights on 24 hours a day, a speci- no detailed time-series data, and there is a large uncertainty
fier may require excellent efficacy and accept subpar color regarding actual lighting electricity consumption. The recent
q
uality. On the other hand, a museum may require superior lighting market characterization for 2010 from DOE (2012)
color and be willing to sacrifice efficacy. estimates that electricity consumption for lighting in the
Good color rendering can be achieved with such discon- residential, commercial, industrial, and outdoor stationary
tinuous light spectra because of the properties of the other sectors is 175 terawatt hours (TWh), 349 TWh, 58 TWh,
two elements in the process of perceiving object colors: the and 118 TWh, respectively, thus totaling 700 TWh for all
reflectance of the objects and the absorption of the cone sectors. Another recent estimate, from the Energy Informa-
photopigments in the human visual system. All objects, tion Administration (EIA, 2011), suggests that in 2010 the
natural or artificial, reflect as a function of wavelength in a residential and commercial sectors used about 499 TWh
very broad and continuous manner. The reflectance factors of of electricity for lighting, which corresponds to roughly
these objects (the proportion of light reflected as a function 18 percent of the total electricity consumed by both of those
of wavelength) do not show sudden spikes or isolated dips sectors.7 The most recent (2006) EIA data available for the
in reflectivity across the visible spectrum. Because of this, manufacturing sector show 63 TWh consumed in lighting,
the general shape of the reflectance factor can be interpolated which corresponds to 7 percent of all electricity consumed
with fairly coarse wavelength sampling. The three cone by manufacturing and 2 percent of all electricity used by the
photopigments responsible for color vision have absorption United States (EIA, 2009).
functions that are very broad, continuous, and overlapping DOE (2012) reports a breakdown by technology type for
in wavelength sensitivity. Each cone type responds to many each sector, estimating that in the commercial sector linear
wavelengths, although sensitivity does change depending fluorescent lamps are responsible for 72 percent of light-
on the wavelength. The outputs of these photoreceptors do ing electricity consumption, and that the residential sector
not signal the wavelength composition of the stimulus to the is still dominated by incandescent lamps (accounting for
brain. For instance, a certain level of activity from one cone 78 percent of residential lighting electricity consumption).
type could result from a small amount of energy at every In 2010, incandescent lamps accounted for 45 percent of
wavelength it is sensitive to or a lot of energy at only one lamps for all sectors in the United States. Linear fluorescent
wavelength it is sensitive to. The visual system makes abso- lamps and CFLs together now account for a larger share in
lutely no distinction between these two situations (Rushton, terms of number of lamps (48 percent), while LEDs account
1972). The perception of color arises from combining and for 0.8 percent. In terms of shipments, the Buildings Energy
comparing the activity among the three cone types. There- Data Book (DOE, 2011) estimates that ENERGY STAR®
fore, countless combinations of input wavelengths can lead lamps8 were 15 percent of total shipments of medium screw-
to the exact same perception of color. These circumstances, based lamps in 2009. Overall, there is a lack of data on annual
in which objects reflect in a fairly predictable manner and market characterization, which are crucial to understand the
the visual system interprets incoming light in terms of three impact of current and future policies.
broadly sensitive channels, allow a great deal of flexibility
for the spectral content of light sources. A recent study dem-
CONTENT OF THE REPORT
onstrated an extreme case of this in which light sources were
developed composed of only four lasers (i.e., sources with Chapter 2 provides an in-depth look at the suite of
extremely narrow emission spectra) with high color render- instruments—R&D investments, standards, demonstra-
ing quality (Neumann et al., 2011). tion projects, and so forth—by which governments have
stimulated more efficient use of energy for illumination. The
FINDING: A light source need not emit energy at every chapter also includes a case-study of early-generation CFLs
visible wavelength in order to achieve high color quality in order to extract lessons applicable to the introduction of
(Figure 1.9). An understanding of the spectral power distribu- SSL products in the market. Chapter 3 discusses the two
tion’s effects on luminous efficacy and the color properties of candidate technologies for manufacture of SSL products—
a light source will enable SSL developers to optimize energy LEDs and OLEDs—and evaluates the barriers remaining to
efficiency while maintaining good color quality. 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
CURRENT LIGHTING CONSUMPTION
luminaires themselves and the challenges to their assembly
IN THE UNITED STATES
At the beginning of this chapter, we briefly described the 7 EIA reports that it does not have an estimate for only public street and
U.S. electricity use by sector. Concerning the contribution highway lighting, but these applications are considered part of the com-
mercial sector in the EIA report and are thus included in the 499 TWh.
of lighting to overall electricity consumption, it is generally
8 ENERGY STAR® is a voluntary program created by DOE and the
agreed that nearly 20 percent of U.S electricity generation is
Environmental Protection Agency to encourage energy efficient products
used in lighting (Azevedo et al., 2009). However, there are and buildings through labeling. Discussed in Chapter 2.
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INTRODUCTION 15
and integration into buildings and electricity systems. Chap- either standard incandescent or halogen. The low-voltage
ter 5 provides a perspective on the design and installation of MR-16 lamp (Figure 1.14) commonly used in accent, task,
LED and OLED luminaires. Chapter 6 discusses the market and display lighting uses halogen technology.
barriers to the adoption of SSL products. 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
ANNEX
4-foot tubes. They are often installed in recessed luminaires
There are many different kinds of lamps. Most of the in the ceiling or are pendant-mounted from the ceiling. All
lamps used in residential applications are omnidirectional fluorescent lamps require a ballast. CFLs are available with
(emit light in all directions) incandescent lamps, typically screw bases and an integral ballast (Figure 1.15) for use as
with a medium screw base (Figure 1.12) that fits into most replacements for incandescent lamps or with pin bases for
residential luminaires. In addition, there are candelabra and use with a separate ballast (Figure 1.16). Both CFLs and
intermediate base lamps that are commonly used in residen- linear fluorescent lamps produce light by exciting phosphors,
tial applications, especially in chandeliers and wall sconces. which then fluoresce, with ultraviolet energy. A small amount
Incandescent lamps produce light by heating a tungsten fila- of mercury is added to the lamp to emit ultraviolet light at a
ment to a temperature of approximately 2,500 K to 3,000 K suitable wavelength for exciting the phosphor.
where the filament glows or incandesces. High-intensity-discharge (HID) lamps are electric lamps
Halogen lamps are incandescent lamps in which the with tubes filled with gas and metal salts. The gas initiates an
tungsten filament has been enclosed in a capsule containing arc, which evaporates the metal salts, forming a plasma. This
a halogen gas, typically bromine, which allows the filament results in an efficient and high-intensity light source. These
to operate at a slightly higher temperature without reduc- lamps are suitable for both indoor and outdoor applications
ing the rated life and resulting in a somewhat higher light and are generally used to light large spaces or roadways. All
output than the standard incandescent lamp. Halogen lamps HID lamps require a ballast.
are available that emit light omnidirectionally, as well as Mercury vapor, metal halide (Figure 1.17), and high-
directional varieties, often known as reflector lamps. Reflec- pressure sodium lamps are examples of specific types
tor lamps are designated by the properties of their reflectors, of HID lamps. HID lamps require a warm-up period to
such as PAR (parabolic aluminized reflector (Figure 1.13) or reach stable output as well as a cool-down period before
MR (multifaceted mirror reflector), and are most commonly restarting.
FIGURE 1.12 Incandescent with medium screwbase (A-19). FIGURE 1.13 PAR 20 lamp (tungsten halogen).
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16 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING
FIGURE 1.14 MR 16 lamp (tungsten halogen).
FIGURE 1.16 Fluorescent lamp (T5) without integral ballast.
FIGURE 1.17 Metal halide lamp (an example of high-intensity
discharge lamp).
FIGURE 1.15 Compact fluorescent lamp (screw base with integral
ballast).
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INTRODUCTION 17
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