Assessment of Solid-State lighting Products


Lighting products used in illumination or luminaires are used to illuminate an environment with electric light sources. Generally, a product has, at a minimum, a fixture envelope, a light source, and an electrical connection to a power source. Examples include downlights, troffers, outdoor area and streetlight luminaires, under-cabinet luminaires, chandeliers, and others. The interest in using white solid-state light sources for illumination applications started in the mid-1990s. Today, the technology, specifically the inorganic light-emitting diode (LED), has matured to a point that these solid-state lighting (SSL) products, both luminaires and integral replacement lamps (i.e., those containing the electronics for the replacement lamp that are not otherwise present in the incumbent luminaire), are able to compete well with some traditional technologies in certain applications.

Even though the replacement lamp is a subcomponent of a luminaire product, in some sense the replacement lamp is also a self-contained product. Therefore, in this chapter we call both the complete luminaire and the integral replacement lamp a product. Ultimately, the lighting product’s (i.e., the luminaire’s or the integral replacement lamp’s) performance in a given application is what matters most to the purchasers and end users of that product. In this chapter we look at each subcomponent of a lamp or luminaire and its performance and then address the luminaire and integral lamp products and issues related to their overall performance. This chapter addresses only products that produce white light, created by either mixing color (red, green, blue, yellow) or downconverting with a phosphor.


Typically, an SSL product consists of several subcomponents, including:

•   An LED, an LED array, an integral lamp, or an organic LED (OLED) panel;

•   Secondary optics to control the distribution of the light;

•   Heat sink, thermal management components, or thermal interface material (TIM); and

•   Driver and control devices.

FIGURE 4.1 illustrates these components for a screw-base A-lamp LED replacement.

Some luminaires integrate the light source(s) with the luminaire envelop and other product components, meaning the light source cannot be easily removed and replaced or repaired. Some luminaires with integrated light sources are considered retrofit luminaires and are to be used in whole product replacement. Other luminaires have replaceable lamps (with a screw base or pin base), including A-lamps, linear fluorescent lamps (LFLs), compact fluorescent lamps (CFLs), multifaceted reflector (MR) and parabolic aluminized reflector (PAR) lamps, and others. Figure 4.2 illustrates a luminaire with integrated light sources and a luminaire with a replaceable lamp.

Luminaires with integrated light sources offer a number of advantages compared to luminaires with replaceable lamps. The luminaire designer/manufacturer has more control over the entire product (e.g., electronic components, thermal management design, optics, etc.) and can select the components to optimize performance. In contrast, a developer of replacement lamps must consider all of the possible luminaires within which a product may be installed and design a product to optimize compatibility rather than performance.

LED Replacement Lamps

After the phase-out of certain types of incandescent lamps between 2012 and 2014, consumer choices for replacing these types of screw-in lamps will include higher efficacy halogen incandescent lamps, CFLs, and LED lamps. Many SSL product manufacturers are producing screw- and pinbased lamp products to replace incandescent, halogen, compact

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4 Assessment of Solid-State Lighting Products INTRODUCTION • Secondary optics to control the distribution of the light; Lighting products used in illumination or luminaires are • Heat sink, thermal management components, or used to illuminate an environment with electric light sources. thermal interface material (TIM); and Generally, a product has, at a minimum, a fixture envelope, • Driver and control devices. a light source, and an electrical connection to a power source. Examples include downlights, troffers, outdoor area Figure 4.1 illustrates these components for a screw-base and streetlight luminaires, under-cabinet luminaires, chan- A-lamp LED replacement. deliers, and others. The interest in using white solid-state Some luminaires integrate the light source(s) with the light sources for illumination applications started in the luminaire envelop and other product components, meaning mid-1990s. Today, the technology, specifically the inorganic the light source cannot be easily removed and replaced or light-emitting diode (LED), has matured to a point that these repaired. Some luminaires with integrated light sources are solid-state lighting (SSL) products, both luminaires and inte- considered retrofit luminaires and are to be used in whole gral replacement lamps (i.e., those containing the electronics product replacement. Other luminaires have replaceable for the replacement lamp that are not otherwise present in the lamps (with a screw base or pin base), including A-lamps, incumbent luminaire), are able to compete well with some linear fluorescent lamps (LFLs), compact fluorescent lamps traditional technologies in certain applications. (CFLs), multifaceted reflector (MR) and parabolic alumi- Even though the replacement lamp is a subcomponent of nized reflector (PAR) lamps, and others. Figure 4.2 illustrates a luminaire product, in some sense the replacement lamp is a luminaire with integrated light sources and a luminaire with also a self-contained product. Therefore, in this chapter we a replaceable lamp. call both the complete luminaire and the integral replacement Luminaires with integrated light sources offer a number of lamp a product. Ultimately, the lighting product’s (i.e., the advantages compared to luminaires with replaceable lamps. luminaire’s or the integral replacement lamp’s) performance The luminaire designer/manufacturer has more control over in a given application is what matters most to the purchasers the entire product (e.g., electronic components, thermal and end users of that product. In this chapter we look at each management design, optics, etc.) and can select the compo- subcomponent of a lamp or luminaire and its performance nents to optimize performance. In contrast, a developer of and then address the luminaire and integral lamp products replacement lamps must consider all of the possible lumi- and issues related to their overall performance. This chapter naires within which a product may be installed and design a addresses only products that produce white light, created product to optimize compatibility rather than performance. by either mixing color (red, green, blue, yellow) or down- converting with a phosphor. LED Replacement Lamps TYPES OF SSL PRODUCTS After the phase-out of certain types of incandescent lamps between 2012 and 2014, consumer choices for replacing Typically, an SSL product consists of several subcompo- these types of screw-in lamps will include higher efficacy nents, including: halogen incandescent lamps, CFLs, and LED lamps. Many SSL product manufacturers are producing screw- and pin- • An LED, an LED array, an integral lamp, or an based lamp products to replace incandescent, halogen, com- organic LED (OLED) panel; 57

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58 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING (a) (b) FIGURE 4.1  An LED equivalent of a screw-base A-lamp showing the component parts. Courtesy of Philips Lighting. pact and linear fluorescent, and metal halide lamps. This is an appealing market segment for several reasons. The large number of available sockets appeals to the manufacturing community, and the lower investment required to try these products by directly replacing the older lamp in the existing luminaire appeals to the consumer. Although the LED chips themselves are manufactured by a small number of multi- national companies, the assembly of an LED lamp resembles that of any electronic equipment. The investment needed to set up an assembly line is relatively modest, and therefore FIGURE 4.2 Two types of LED luminaire: (a) with integrated a very large number of companies can and have entered the LED light source; (b) with replaceable LED module. Courtesy of industry. The approximately 4 billion medium screw-base Toshiba. sockets in U.S. households represent a very attractive poten- tial market, so the industry development has happened very quickly, in the span of only a few years. At the same time, the industry1 is scrambling to develop meaningful safety and performance standards, and product quality varies over a wide range. Figure 4.3 through Figure 4.5 illustrate examples of LED replacements for incandescent A-lamps, PAR lamps, and linear fluorescent lamps. The lamp on the left of Figure 4.3 uses the remote phosphor concept where the blue LEDs excite the orange phosphor cover (which emits white light), and the lamp on the right uses two phosphor white LEDs2 placed within an envelope that mimics an incandescent A-19 lamp. 1 Primarily the National Electrical Manufacturers Association (http:// FIGURE 4.3  Sample LED replacement lamps for incandescent www.nema.org) and the Zhaga Consortium (www.zhagastandard.org). A-19 lamps. Courtesy of Philips Lighting. 2 See the discussion of white phosphor LEDs in the subsection of C ­ hapter 3, “Use of Phosphors.”

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ASSESSMENT OF SOLID-STATE LIGHTING PRODUCTS 59 There are many challenges for making reliable replace- ment A-19 lamp replacements. An LED replacement lamp for an incandescent A-lamp requires squeezing all the needed components, LEDs, driver, heat sink, etc., into a light-bulb sized package as shown in Figure 4.3. Heat dissipation is very challenging and could affect the reliability of the LED lamp. At the present time, in early 2012, it is difficult to make long-life, reliable, LED replacements for incan- descent A-19 lamps greater than 75 W because of thermal management challenges. There are some high-power PAR replacement lamps that use active cooling in which a fan is employed to move air and remove heat by convection. However, active cooling usually is not desirable in lighting FIGURE 4.4  Sample LED replacement lamp for incandescent products because of additional failure modes and audible parabolic aluminized reflector lamps. Courtesy of OSRAM noise issues. Realizing these limitations, an industry group, S ­ YLVANIA and Paul Kevin Picone/PIC Corp. Zhaga Consortium,3 is developing a standard for a better socket for replacement lamps with better heat dissipation characteristics, among other attributes. Even though the new socket may help lamps and luminaires in the future, it will not help replacement lamps for existing luminaires. Many of the LED A-19 replacement lamps currently in the market (early 2012) cannot be considered as true replacement for the following reasons: • LED replacement lamps have a larger geometric shape than the incandescent lamp they are meant to replace and may not fit into a luminaire that was designed for incandescent A-19 lamp. • The spatial beam distribution of the LED replace- ment lamps is not similar to that of the lamps they are designed to replace. For example, in a common table lamp, LED replacement lamps often will cast light in a more upward direction, leaving the tabletop FIGURE 4.5  Sample LED replacement lamp for linear T8 fluo- surface below relatively dark. rescent lamp. Courtesy of Pacific Northwest National Laboratory. • Although a wide variety of LED replacement lamp products are commercially available, their initial purchase price is much higher than that of competing The luminous efficacy of LED replacement products lamp technologies. However, the “Lighting Facts” has improved over the past several years and is expected to labels that appear on lamp packages provide con- continue, as illustrated in Figure 3.1 of Chapter 3. Figure 4.6 sumers an estimate of annual operating costs, which illustrates examples of performance data for replacement allows rough calculation of payback times. LED-integral lamps (A-lamp, PAR lamp, and linear lamps), reported in 2011. The efficacy values of these replacement Retrofit Luminaires lamps are in the range of 40 to 110 lumens per watt (lm/W). Several LED replacement A-19 and PAR lamps are showing Retrofit luminaires are SSL products that fit into the very promising results in terms of efficacy. spaces occupied by existing luminaires but require complete A few LED replacements for 4-foot linear fluorescent tubes removal of the existing luminaire for installation. Common have performance similar to traditional fluorescent lamps, but types of retrofit luminaires are those for recessed housings, for many of them the total light output is substantially lower, 2′ × 2′ or 2′ × 4′ recessed troffers, high-bay luminaires, track and the spatial distribution of light is far more concentrated than that of the conventional fluorescent lamps. The narrow 3 “Zhaga is a consortium, a cooperation between companies from the spatial distribution and relatively low luminous flux mean that international lighting industry. The cooperation is governed by a consortium closer spacing of luminaires would be required to achieve agreement that defines rules regarding confidentiality, intellectual property, the same lighting environment as produced by conventional and decision making. Zhaga enables interchangeability of LED light sources made by different manufacturers. This simplifies LED applications for fluorescent lamps. general lighting” (Zhaga Consortium, 2012).

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60 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING 120 100 80 Efficacy (lm/W) 60 40 A-lamps (Energy Star rated) 20 PAR lamp (Energy Star rated) Linear lamps (Lighting Facts database) 0 0 500 1000 1500 2000 2500 3000 3500 Light output (lm) FIGURE 4.6  Performance data for LED replacement lamps. SOURCE: See http://www.energystar.gov, http://www.­ightingfacts.com. 4.6.eps l lighting products, pendant lights, and roadway luminaires. the ENERGY STAR® program, U.S. Department of Energy’s Although less constrained by “existing holes in the ceiling,” Lighting Facts, CALiPER, and Gateway programs are places other LED products that might be categorized as retrofit where one can gather information regarding the performance luminaires include under-cabinet lights, showcase lights, of commercial LED lighting luminaires (Next Genera- pathway lights, and rope lighting products. These products tion Luminaires, 2012; DOE, 2012). Figure 4.7 illustrates take on similar forms to existing non-SSL luminaires. examples of 2011 performance data for downlight luminaires Of this category of products, the most attention has for commercial lighting applications. As seen, in 2011, the been paid to SSL roadway lighting luminaires. While most luminaire efficacies of ENERGY STAR®-rated LED down- of these luminaires produce luminous flux comparable to lights are in the range 35 to 85 lm/W. In comparison, CFL incumbent technologies, a few are significantly dimmer and halogen downlights are in the range of 10 to 30 lm/W. (National Lighting Product Information Program, 2010; Even though LED luminaires have greater luminous effi- DOE, 2012). Some of the advantages of LEDs, such as long cacy than traditional light source luminaires, LED luminaires life, high performance in cold environments, and robustness, can have greater lamp to lamp color variation, glare, and make SSL very attractive for many roadway applications. flicker and cannot be dimmed. As with replacement lamp products, however, the spatial distribution of light is very different from many SSL road- FINDING: While the majority of LED products in the way luminaires than from other types of light sources. This marketplace have better luminous efficacy than traditional is frequently a disadvantage, because consumers expect a lighting technologies, for many of them, other quality fac- replacement product to behave identically to the preceding tors, such as useful life, color appearance and rendering technology. Some outdoor luminaires have significant glare, properties, beam distribution, flicker, and noise, may be which is not desirable. inferior to traditional lighting products. Even though the One advantage is that the LED luminaire has the opportu- optimistic view is that energy has been saved by using SSL nity to direct light more toward the task, thus reducing wasted technologies, if other factors such as system life, lamp-to- light and helping to control light pollution. lamp color variation, glare, flicker, and dimming, do not meet Another application where retrofit luminaires with LED user expectations, they could slow down market adoption of have done well is recessed cans. Websites including those of SSL technologies.

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ASSESSMENT OF SOLID-STATE LIGHTING PRODUCTS 61 products with the performance and price necessary for wide- spread adoption. LED and LED Array As described in Chapter 3, white LEDs are commonly made by dispersing phosphor(s) in the encapsulant surround- ing the blue (or near-ultraviolet) LED chip. The process of combining phosphors with the LED chip has evolved over the years. Some packages still use the original method of mixing phosphor(s) into an epoxy or silicone medium. Other pack- ages use a layer of phosphor conformally coated on the chip, while newer LED packages and products consist of phosphor layer(s) separated from the LED chip(s), commonly referred to as a remote-phosphor LED or product (Hoelen et al., 2008; Narendran et al., 2005). Remote phosphor-type LEDs minimize heat-induced efficiency loss in phosphors (pro- vided the phosphor conversion efficiency is not very low as well as the absorption of phosphor-converted photons by the blue LED chip). An LED array is created by mounting and inter­ onnecting individual LED devices on a printed circuit c board, which is then connected thermally to the heat sink. OLED Panel FIGURE 4.7  Sample performance in 2011 of commercial LED downlights. SOURCE: See http://www.energystar.gov. A unique feature of OLED lighting is that the device itself can form the installable fixture because of its ability to be fabricated on any particular substrate or shape. Indeed, OLEDs can be fabricated directly on plastic blocks, flexible As with most SSL lighting products, retrofit luminaires metal or plastic foils, or glass. In its configuration as an area have higher initial costs than competing technologies. How- lighting source, as discussed in Chapter 3, the luminaire ever, they are becoming more widely used in applications itself operates without a significant increase in temperature where maintenance costs are high. above the room ambient. That is, in appropriately packaged devices, at a high surface luminance of 3,000 cd/m2, the luminaire temperature rise can be only a few degrees centi- Subcomponents of an SSL Product grade, creating no local or distributed heat load on the room SSL products in the commercial market employ a vari- environment. ety of LED white light sources, including an array of phosphor-converted LEDs (blue LED chips covered by a Secondary Optics coating of phosphor); an array of cool white (i.e., high color temperature) LEDs combined with red LEDs to create a In an LED lighting product, secondary optics are needed warmer white and feedback control to maintain light output to tailor the output beam of a lighting product. LED products and color; and an LED array with a mixture of multicolored commonly designed for illumination applications have LEDs (red, green, blue, etc.) LEDs. These LEDs or LED arrays arranged in several different ways together with secondary are mounted on a heat sink to minimize the heat at the LED optics. These designs include an LED array placed inside junction(s) and are powered by an electronic driver that reflector(s) and behind total internal reflection (TIR) lenses. produces power of the form required by the LED. In some These methods help the collection and distribution of light cases, secondary optics are used to direct the beam in a spe- in a specific manner. Refractive optics, commonly referred cific manner. If the LEDs are packaged as an integral lamp to as lenses, reflective optics, or reflectors, are generally to replace a traditional light source, the lamp envelope (i.e., designed as non-imaging optics to be used in illumination glass bulb) is designed to mimic the form of the traditional products for beam shaping. Researchers have designed and source and includes a specific connector (e.g., an American used complex optics to achieve difficult beam shapes (Tsais National Standards Institute (ANSI) standard base). and Hung, 2011). This section analyzes these subcomponents, their state Typically, no secondary optics are required for OLED of the art, and what improvements are needed to produce panels.

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62 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING Reliability of Optics rials have very low thermal conductivities. As a result, the majority of the heat produced at the p-n junction is conducted Lens materials are usually made from glass, polymers, through the metal substrate below the chip and not through epoxies, or silicones. Material selection is very important, the transparent encapsulant. Usually, a high-power LED is especially when designing long-life products. Some optical mounted on a metal-core printed circuit board (MCPCB). materials degrade when exposed to radiation (more spe- When creating a product, an LED (or an array of LEDs) cifically, short wavelengths like ultraviolet (UV) and “blue” mounted on an MCPCB is attached to a metal heat sink using radiation) and heat. This spectrally dependent light output a TIM. Usually these heat sinks have extended surfaces, deterioration is one of the main ways that LEDs degrade. such as fins, which dissipate the heat to the environment by convection and radiation. Currently, a few manufacturers Thermal Management have started to mount the LED directly onto the heat sink to further reduce the thermal resistance from the junction to the Thermal management is very important to enable reli- environment and also to reduce the overall cost. able, long-life LED products, and the thermal management Common thermal interface materials are solder, epoxy, components in an LED product constitute a large fraction thermal grease, and pressure sensitive adhesive. Parameters of product cost. A high-temperature LED junction can that can influence thermal resistance include: surface flat- negatively impact LED life and optical performance, and as ness and quality of each component, the applied mounting discussed in Chapter 3 in the section “An LED Primer,” this pressure, the contact area, and the type of interface material places considerable demands on the plastic lens and encap- and its thickness. Adding conducting particles and carbon sulant material. At higher p-n junction temperatures, the nanotubes (CNTs) to TIM to reduce thermal resistance has amount of photons emitted decreases and the spectral power been studied (Fabris et al., 2011). distribution shifts to longer wavelengths. Furthermore, the Most manufacturers exploit both conduction and convec- degradation of the encapsulant and the LED chip, over time, tion methods to reduce LED junction temperature. Usually decreases the luminous flux. Electrical energy not converted the heat sinks have a very large metal surface area, and, as to light contributes to the heat at the p-n junction. To keep a result, the integral lamp or the entire luminaire is much the LED junction temperature low, all heat transfer methods, heavier than its traditional counterpart. Figure 4.8 shows including conduction, convection, and radiation, must be typical weights for incandescent, CFL, and LED lamps of considered. Heat conducted to the environment from the p-n different types. junction encounters several interfaces and layers. Therefore, To make the weight of LED products comparable to to keep the junction temperature low, the thermal resistance traditional lamps, lightweight materials, like polymers of every layer and interface must be very low. and composites, with very high thermal conductivity are needed. The thermal conductivity of plastic materials can Thermal Management Component and Strategies be increased by using fillers such as ceramics, aluminum, graphite, and so on. Injection-molded polymer parts of high An LED chip is typically encapsulated in a transparent thermal conductivity are an economical approach for cool- material, such as epoxy, polymer, or silicone. These mate­ 24 oz 16 oz 8 oz 0 oz INC CFL LED INC CFL LED INC CFL LED INC CFL LED A19 PAR20 PAR30 PAR38 FIGURE 4.8  Weight comparisons among incandescent (INC), compact fluorescent (CFL), and LED lamps for A19, PAR20, PAR30, and PAR38 lamp types. SOURCE: Narendran (2012). 4.8.eps

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ASSESSMENT OF SOLID-STATE LIGHTING PRODUCTS 63 ing high power LED products. Some also have investigated lifetime scales roughly inversely with current (and therefore, techniques such as heat pipes, like those used in computers, brightness). Also, it is known that for every 10°C increase in to keep LED junctions cooler. temperature the OLED lifetime decreases by approximately While these passive cooling methods work well for certain 30 percent (see Chapter 3). Hence, thermal degradation types of SSL products, higher power LED lighting products becomes a limitation at very high brightness. Up until now, (1,500 lumens and above) pose significant thermal manage- this has prevented the application of OLEDs to high intensity ment challenges. Passive heat sinks are not sufficient to keep or specular lighting applications. Further research, however, the LED junction sufficiently cool. Therefore, to achieve directed at developing molecular materials and device archi- desired lumen values in a small form factor (e.g., A-lamp, tectures that are more robust and, therefore, can more easily PAR lamp, MR 16, etc.), active cooling may be required to withstand these extreme operating conditions can result in dissipate the heat. Even though mechanical fans have been a much expanded application domain for OLEDs. Continu- used in some high-power LED lighting products (Ecomaa ous improvements in brightness and lifetime, however, are Lighting Inc., undated; Peters, 2012), they are not desirable being made by researchers across the globe. If such high- for many reasons, including short life, acoustic noise, attrac- brightness-spot OLED sources are successfully developed, tion of dust, and increased energy use. Over the past several the other useful features of this lighting technology may years, other active cooling techniques have been investigated eventually dominate the SSL market. for managing the heat in high-power electronics, including synthetic jet and piezoelectric fan technologies. Synthetic FINDING: OLEDs are typically low-intensity, large-area jet technology uses a moving diaphragm that produces air lighting sources. However, numerous applications require movement by suction and ejection of air. Rapidly fired pulses more intense, specular lighting as afforded by LEDs. The of air are directed to where cooling is needed, such as heat lifetime of OLEDs are negatively impacted by high currents sink fins, to improve cooling efficiency. Piezoelectric fans used to generate high brightness. have several advantages, including longer life, lower acoustic noise, and lower power demand (Zhang et al., 2011). These RECOMMENDATION 4-2: The Department of Energy techniques have shown promise and are worthwhile for fur- should invest in research that can lead to small area but high- ther development for high-power LED cooling (Acikalin et intensity lighting systems with organic light-emitting diode al., 2007). Even though active cooling may be necessary for for use in directional illumination applications. some products in some applications, for the majority of the applications, passive cooling is more desirable. Electronic Drivers There is a strong interaction among LED device efficacy, the requirement placed on the thermal management system, The light output of an LED is proportional to its drive cur- and the cost of SSL. Increased efficacy reduces the heat rent, which is typically direct current (dc), and this current is generated per lumen, allowing either a shrinking of the nec- supplied at a relatively low voltage. To provide the appropriate essary heat sink, and thus a reduction in cost and weight, or dc current and voltage, an electronic circuit known as a driver an increase in lumen output for the same physical luminaire. is inserted between the alternating current (ac) line voltage and the LED. This electronic driver can be incorporated FINDING: LED efficacy strongly leverages cost, physi- within a lamp product, as for the A-lamp LED replacement, or cal size, and weight of SSL luminaires. as a separate device located external to the luminaire. RECOMMENDATION 4-1: The Department of Energy Integral Drivers in LED Replacement Lamps should place a high priority on research directed at increasing the efficacy of LEDs. The LED replacement lamp has an integral driver, illus- trated in Figure 4.1, that enables the lamp to be connected directly to the line voltage socket. The medium screwbase Thermal Management for OLEDs lamp offers very little space for the built-in or integral driver, One of the advantages of OLEDs is that the thermal man- so thermal challenges for the electrical components can be agement challenge is less stringent than for LEDs because significant. The drivers utilize electrolytic capacitors for their heat density is very low because of their large surface energy storage on the dc side of their ac-to-dc converters, area. Indeed, it is found that at a surface luminance of and they are likely going to be the weakest link in these 3,000 candlea per square meter (cd/m2), OLED panels typi- products and limit the product lifetime. The maximum cally operate in room environments cooled only by natural temperature ratings of these capacitors are typically in the convection, at 5-7°C above room temperature. However, 105°C to 125°C range, at which temperature their life ratings many applications require high-intensity spot sources. In are 5,000 to 10,000 hours. Each 10°C reduction in operating fact, very high luminances (>10,000 cd/m2) have been dem- temperature increases the capacitor life by roughly a factor onstrated for OLEDs, but, unfortunately, their operational of 2, giving the driver designer the challenge to maximize the

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64 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING driver life while also providing the required output power. manufacturers of the different component parts of an LED This challenge is the hardest for drivers that are integral to luminaire forming loose alliances to make certain that the screw-based lamps, because they cannot be moved far from products work together. It is also reasonable to expect a high the heat source. level of obsolescence of driver designs, with older designs For these reasons, the rated wattage of available LED lamps being replaced by those having different features during the is still fairly small. The luminous efficacy of the LED devices time that the industry remains without standards. Indeed, has increased to a point where a lamp with a light output equal the early designs from different manufacturers have been to a 60 W incandescent lamp consumes only 10 W. However, quite unique and not compatible with one another, so direct because of the thermal challenges, a 100 W equivalent lamp replacement of components within the LED luminaire, and has not yet become available. As a result, screw-in LED lamps sometimes even the replacement of the entire luminaire, can that are used as incandescent replacements in existing instal- be challenging. Leading companies have recognized the need lations are at present limited to the lumen output of a 60 W to rapidly develop standards, at least for the interconnections incandescent lamp, although a 75 W equivalent has recently between the various components within the LED luminaire. been made available. As a result, the Zhaga Consortium was formed to develop these standards. Non-Integral Drivers FINDING: Because of the large number of different Commercial-grade LED luminaires are not constrained ways to construct an LED lamp, industry has recognized the to use any particular form factors for the components. This need for some levels of standardization and has organized to is because luminaire replacement in commercial build- develop such standards. ings is easier in dropped ceiling-type construction where there is ample room for luminaire housing and components, The long expected life of an LED light engine will put and replacement is, therefore, more readily performed. The pressure on the driver designer to produce designs that have drivers in these luminaires are typically separate from the equally long life ratings. Just as with integral drivers in LED module, and the luminaire may be designed so as not to incandescent replacement lamps, the weakest link in a non- present a thermal problem for the drivers. There is a trend in integral LED driver is the electrolytic capacitor that is used the industry to design “universal” drivers that produce either for energy storage in the ac-to-dc converter that is part of the constant voltage or constant current output to the LED with driver. Research into other types of energy storage devices, input voltage ranging from 100 Vac to 277 Vac, which covers perhaps ceramic capacitors with high capacitance and small almost all global requirements. Having said that, today manu­ size, may become necessary, and funding for it should be facturers of these drivers—quite often the same companies considered. Another way to solve this problem may be to that also produce ballasts for fluorescent lamps—­ roduce a p create a new building infrastructure, where the ac-to-dc con- wide array of products with differing specifications, while version is performed centrally, nearer to the utility entrance they are jockeying for market position. Standardization in the to the building. This enables the building to use only a few industry has started in some areas (see, for example, NEMA larger power ac-to-dc converters that may not be as cost (2010a) and emerging standards by the Zhaga Consortium constrained as in the case when the conversion is performed (2012)), especially for the interconnections between different in every luminaire. At least one industry group, the EMerge components within the SSL luminaire (e.g., for standard- Alliance,4 has been formed to investigate the possibility of a izing electrical, mechanical, and thermal connections of the new electrical infrastructure and start the development of LED luminaire, including the LED module, the heatsink, standards in this area. This application is currently limited to the driver, and any lighting controls). commercial buildings that use a dropped ceiling consisting Most currently available drivers for interior lighting appli- of a ceiling grid and ceiling tiles, because it is envisioned cations have relatively low output power, up to around 40 W. that the elements of the ceiling grid are going to become the Some higher-output drivers, typically rated around 100 W, electrical conductors. do exist for outdoor and industrial high-bay applications. It is likely that higher-output drivers will be needed in both Drivers for OLEDs interior and exterior applications in the future, when higher- light-output LED modules become available. The construc- The driver industry for OLEDs is at its infancy. It can tion complexity of these products is similar to electronic reasonably be expected that the driver would look similar to, ballasts for fluorescent lighting, and their assembly can be if not be the same as, a driver for LEDs, because the electrical performed anywhere in the world. The potential number of requirement of both light engines are very similar. However, different output configurations of LED drivers is much larger only a few experimental OLED luminaires have been pro- than for fluorescent lamps, mainly because fluorescent lamps duced so far, and experience driving them is limited. Both are quite standardized, while LED designs are not. This may lead to fragmentation in the market in the short term, with 4 Further information is available at http://www.emergealliance.org.

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ASSESSMENT OF SOLID-STATE LIGHTING PRODUCTS 65 LEDs and OLEDs are current-driven devices and can work to the luminaire, so the development of SSL technology has using either dc or ac supplies. Given that the line source is practically no effect on the design of the former or compat- an ac voltage supply, the OLED driver must convert voltage ibility with SSL luminaires. to current. Luminance then, is controlled by the current in a In the case of incandescent or incandescent halogen nearly linear fashion. Hence, there is a roughly linear depen- lamps, the lighting control device that connects directly to the dence of luminance on current. The current-versus-voltage luminaire is either a switch or a dimmer. Switches are avail- (I-V) characteristic of an OLED follows a power law, I ~ Vm, able in two forms, mechanical and electronic. A mechanical where the dimensionless ratio m = B/T has values between 3 switch consists of metal switch leaves that open to form an and 7. Here, B is a constant, and T is the temperature. This is “air gap” (a physical disconnect) to disrupt electric current in contrast to that of an LED, where I ~ exp(−AV/T), where to the luminaire and turn the lights off. The actions of open- A is a constant. Hence, as an LED brightness increases, the ing and closing the switch leaves cause electric arcs to be voltage required to achieve a given brightness changes. How- formed that typically last no longer than a few milliseconds, ever, given the relatively constant temperature characteristic but over time this arcing causes the switch contacts to erode, of OLED operation, the voltage-to-luminance conversion thus eventually causing the switch to fail. The introduction required in the driver is simplified compared to that of an of electronic ballasts for fluorescent lighting in the 1980s LED, which requires aggressive cooling to remove heat at was followed by some reports of switch failures, which the highest brightness. However, these products are far from were the result of increased “inrush current” during switch being ready for any kind of standardization. turn-on compared with traditional lighting loads. This led Nevertheless, the large capacitance of an area device, cou- the industry to develop a switch-ballast compatibility stan- pled with a somewhat different current-voltage relationship dard (NEMA, 2011), which is in use today. SSL drivers that for OLEDs versus LEDs present as yet largely unexplored meet that standard are not expected to cause problems with challenges in the development of versatile, efficient, and mechanical switches. electronically robust control electronics for the former tech- Electronic switches also exist in the market. These are nology. Given the relatively early stage of development of used especially in components that are part of a lighting OLED lighting, it is important that issues of lighting control product, in so-called smart switches or smart dimmers. be investigated earlier rather than later to understand what Such devices use a semiconductor switch, typically a device challenges must be met to produce low-cost control systems. called a TRIAC, which can be turned off without creating In particular, the unusual form factor of OLEDs suggest that an airgap to the load. This technology is useful especially in there might be opportunities for integrating such electronics wallbox switches that may be remotely turned on and off, in unusual ways with the luminaires that will provide advan- for example, by using a sensor or handheld device. Typical tages over conventional SSL and other lighting systems. electrical wiring practices do not bring a neutral wire to the wallbox, and, therefore, the microcontroller that con- FINDING: OLEDs are still in their infancy. While the trols the operation of the smart switch or dimmer has to be driver electronics may have many similarities to that of kept “alive” by allowing a small amount of current to pass LEDs, there are some essential differences in their operating through the lighting load when the lamps are in the off state. performance because of the large capacitive load presented (Without such current, the microcontroller would shut off, by OLEDs. and there would be no way to turn the switch or dimmer on.) For conventional lamps this “keep alive” current does not cause inconvenience to the end user because incandescent or LIGHTING CONTROLS fluorescent lights do not emit any light when the current is Lighting controls for electric lighting have existed almost that small. However, more care has to be taken in the design as long as incandescent lamps themselves in the form of of controls for SSL devices. Because of the low wattage of switches and rheostat dimmers that were used primarily in the lamps, even small currents can cause visible light output, theatrical applications. The modern lighting control industry often in the form of flickering when the lights are intended had its beginning in the early 1960s, when the first wallbox5 to be off. The small current charges the capacitors typical in solid-state dimmer for incandescent lamps was commercial- the design of the drivers for these lamps, and the capacitors ized. Since that time, several lighting control devices have in some designs discharge periodically through the lamps, been developed by many companies, such as automatic time causing the flicker. Industry standards are being developed switches and sensors that are used for detecting the presence to address this issue, but there are SSL control products on of people (“occupancy sensors”) or ambient levels of day- the market today that cause this problem. light (“photosensors”). These devices do not connect directly Dimmers for incandescent lighting are available with analog and digital designs. The analog designs are similar to mechanical switches in the sense that they employ a 5 The term wallbox refers to a wall-mounted electrical box that houses mechanical switch producing an airgap when the dimmer is the wiring connections for electrical devices such as light switches, light dimmers, and receptacle outlets. off. However, digital dimmers are in this sense essentially the

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66 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING same as electronic switches, and flickering in the off state is actually increased, meaning that the minimum load require- observed with some SSL lamps. ment in an incandescent dimmer is not the only condition that Additionally, incandescent dimmers can also be cat- needs to be satisfied. Leading edge dimmers that are used in egorized into two main types: “leading edge” (also called commercial grade lighting controls sometimes provide a con- forward phase-cut) and “trailing edge” (also called reverse tinuous gate signal rather than a pulse, and this action is very phase-cut). The former uses a TRIAC as the semiconductor successful in keeping the TRIAC on even with smaller loads. switch, and the vast majority of incandescent dimmers in Additionally, trailing edge dimmers, which use transistor ­ residential buildings are of this type because of the lower switches that require a continuous signal to keep them on cost of the design. The TRIAC is turned on when it receives and are not characterized by a holding current, may also an electrical pulse at its “gate” (one of the terminals of the avoid this problem. Trailing edge dimmers were originally device) and stays on until the electric current falls below designed for low-voltage (incandescent) lighting using an the TRIAC’s “holding current” very near the end of the electronic transformer to step the 120 Volts ac (Vac) line volt- half cycle of the ac wave form, which in the United States age to the 12 Vac required by the lamps. These transformers operates at 60 Hz and ideally (and very closely in practice, were developed to make them lighter, smaller, and also often too) has the form of a sine-wave. The earlier the TRIAC is less expensive than core and coil wound transformers, and turned on in the half cycle, the brighter the lamp operates. they utilize capacitors on the “front end” for energy storage The resulting voltage waveform at the lamp is illustrated inside the device. When a capacitor suddenly experiences a in Figure 4.9. The design of the dimmer converts the user high voltage, a large inrush of current occurs, and many such action—such as moving a slider up and down—to the proper electronic transformers are not compatible with leading-edge timing of this TRIAC gate pulse. The operation of the TRIAC dimmer designs. Trailing edge designs reverse the process is illustrated in Figure 4.9. Electronic switches that employ of switching by turning the transistors on in the beginning a TRIAC simply turn it on at the beginning of the half cycle of the half cycle and turning them off at some point before to operate the lamp at full on. the end of the half cycle. Front end capacitors do not cause The TRIAC works very well with incandescent lighting problems for this mode of operation, so these types of dim- because the TRIAC’s holding current (below which the mers are more compatible with SSL drivers such as those TRIAC will not remain on) is much smaller than the cur- used in medium screw-base incandescent replacement lamps. rent in even the lowest wattage incandescent lamps, such The lighting controls industry is developing new dimmer as a 25 W lamp. However, with CFLs, and even more so designs specifically for LED lamps that are used as replace- with SSL devices that require very low power, the current ments for incandescent lamps. It is reasonable to expect that required to operate the lamps may be smaller than the hold- the lamps will operate well with the new designs, but the ing current, and this can lead to observations of flickering or industry has estimated that there are more than 150 million other improper operation. In addition, other problems have leading-edge dimmers installed in U.S. homes, and it is prob- been observed with keeping the TRIAC reliably in conduc- ably impractical to expect to replace them all as LED lamps tion with certain LED lamps. In some cases, the problems become more popular. NEMA (2010b) has developed a new manifest themselves when the total load (number of lamps) is standard, NEMA SSL 6-2011, to address the retrofit issue, 200 150 100 50 Voltage 120V 60Hz electric supply 0 0 5 10 15 20 voltage to lamp in -50 dimmed waveform -100 -150 -200 milliseconds FIGURE 4.9  Waveforms illustrating leading-edge dimming control. 4.9.eps

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ASSESSMENT OF SOLID-STATE LIGHTING PRODUCTS 67 and lamps that are designed to comply with this voluntary RECOMMENDATION 4-3: Industry should develop standard should operate with the existing dimmers and avoid standards for LED drivers and future generations of lighting such problems as flickering. Such controls, however, may not controls that will ensure that all LEDs that are designated provide the same low-end dimming range that consumers “dimmable” work well with all new dimmers in the future. are used to with incandescent lamps. In addition, the U.S. In the meantime, SSL products should indicate on their Environmental Protection Agency has asked the industry labels that they may not function correctly with presently to develop a testing standard for ENERGY STAR® lamps installed controls. regarding compatibility with controls.6 Together, these ini- tiatives should mitigate most of the compatibility problems, LED lamps offer an additional control opportunity, that or at least provide consumers reasonable options. Finally, of controlling the color of the light output. There have been NEMA and the Zhaga Consortium have started another some proprietary products in the market that offer this standard development (NEMA SSL 7-2012) to address the control function,8 but no industry standards are yet under need for future LED lamps and future dimmer designs to development. It is not yet clear how much value the market provide significantly better dimming performance. These gives to such color control, so the development of these standards will place new requirements on both the lamp and standards may not happen in the immediate future, if at all. the dimmer design. The functionality will probably begin with luminaires that In addition to controlling light levels through ­ immers d have a separate driver using digital communication (such as described above, there are other industry standard as an enhanced DALI that includes additional control func- “­ rotocols” to provide dimming signals to luminaires. These p tions or wireless protocol). Whether screw-in incandescent include 0 to 10 volts DC signals where higher voltages corre- lamp replacements ever develop this functionality remains spond to higher light levels, digital standards such as Digital to be seen. Addressable Lighting Interface (DALI),7 wireless standards An important difference between incandescent lamps such as Zigbee, and various proprietary standards by indi- and both CFLs and LEDs under dimming conditions is vidual manufacturers. In each of these cases, the luminaire that incandescent (and halogen) lamps become warmer, contains a separate fluorescent or high-intensity discharge exhibiting a color shift (in terms of color temperature, (HID) ballast or a separate driver for SSL products that has measured in Kelvin) toward the red, when dimmed. The been designed to be compatible with whichever method of other light sources do not inherently change their color signaling is used. This means that the method of signaling the temperature, which is often viewed as an undesirable feature dimming information is decoupled from the actual dimming by residential consumers. Humans are biologically biased function performed by the ballast or driver, and there is no to prefer red light in lower ambient conditions because of need for new compatibility standards. the same shift in sunlight toward the late evening hours. With the phase-out of incandescent lamps taking place With proper controls and devices emitting the appropriate in Europe, there has been a proposal to develop a new stan- colors, LED lamps and luminaires can mimic the color shift dard for communicating dimming information on the power performance of incandescent lights when dimmed in this line (the so-called “power line carrier” method) to CFL and manner. It should be noted that there is at least some patent LED lamps that would replace incandescent lamps. This is protection9 for this functionality, possibly leading to limited thought to be necessary by some industry representatives choices for consumers. because phase-cut dimming is interpreted to be permissible by European standards only when used with incandescent STANDARDS AND REGULATIONS lamps (International Electrotechnical Commission, 2009). The new standard is now under development, and some LED Product Measurement and Performance people in the industry expect it to be published in late 2012 or early 2013. This would also mitigate any concerns about Standards play an important role in the development total harmonic distortion (THD) and power factor (PF) that and deployment of new technologies as discussed in the have been expressed by power utilities. For more detail, see C ­ hapter 5 section, “Testing and Measurement Standards.” the discussion below, “Electric Power Quality.” During the past several years, several standards have been created, most notably IES LM-79, “Approved Method: Elec- FINDING: LED replacements for incandescent lamps trical and Photometric Measurements of Solid-State Lighting may not work with all existing control infrastructure, espe- Products” (IES, 2008a) and IES LM-80, “Approved Method: cially dimmers. Measuring Lumen Maintenance of LED Light Sources” (IES, 2008b), the latter used in conjunction with IESNA TM-21 to extrapolate estimates of lumen maintenance. More 6 Alex Baker, personal communication with Nadarajah Narendran, Com- mittee on Assessment of Solid State Lighting, August 2012. 8 See for example controls offered by Philips (Color Kinetics). 7 See IEC 62909. 9 See for example U.S. Patents 7,038,399; 7,014,336; and 6,636,003.

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68 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING standards are needed to resolve unknowns that will otherwise that were borrowed from the CFL industry. Manufacturers be left to consumers and other lighting decision-makers. grouping LEDs to single bin for a given correlated color Difficulties can arise with standards when the test con- temperature (CCT) product according to American National ditions do not match those of the installed application. As Standards Institute (ANSI) C78 tolerance area may find the an example, downlight luminaires are typically measured color variation between LEDs very large, to a point that it is according to the IES LM-79 standard that requires the sur- not acceptable for general lighting applications. Presently, rounding ambient temperature to be at 25°C. In practice, the some manu­acturers are using tighter bins to avoid visible f ambient temperature generally will be higher when the light color difference between products. source is recessed in a luminaire. In addition, the tempera- ture is dependent on where the luminaire is located and will FINDING: Additional standards or revisions to stan- be higher on upper floors where the fixture is surrounded dards are needed to resolve unknowns that will otherwise by insulation material. This potential for higher ambient be left to consumers and other lighting decision-makers to temperatures was less of an issue in the past when down- resolve, specifically test procedures and/or de-rating factors lights used incandescent and halogen technologies whose that account for higher temperature environments, where performance was less sensitive to changes in temperature. performance may vary from LM-79 data, and alternatives to But in the case of LEDs, increases in junction temperature LM-80 that can predict whole product life more accurately. can alter the performance. Past studies have shown that in In the case of the latter, research is under way to develop test some cases the light output reduction from the product is procedures to predict whole product life more accurately. significant, more than 30 percent (Narendran et al., 2008), versus the LM-79 data sheet. Practitioners expecting a cer- RECOMMENDATION 4-4: (a) Manufacturers should tain performance may be disappointed if they strictly rely on publish data for photometric quantities and life per industry the product’s LM-79 data. While the use of testing standards standards and de-rating factors for use in typical applications. has worked for incumbent lighting technologies, LM-79 may (b) IESNA should develop a test procedure to predict whole not work for SSL products because of the latter’s sensitivity product life more accurately. (c) ANSI should revise the color to heat. Test procedures specific to the application environ- binning standard to ensure imperceptible color differences ment are an ideal solution but much more costly than a single between two adjacent light sources. procedure for all applications. A compromise solution would be for manufacturers to publish data with de-rating factors Electric Power Quality for use in typical applications. Another important aspect of standards is their quality; that In the United States, power quality is a subject of volun- is, their ability to produce reliable and realistic information tary industry standards, except for electromagnetic compat- about performance. Today manufacturers commonly use the ibility of some lighting equipment, which is regulated by the IES LM-80 procedure to test the lumen depreciation of indi- Federal Communications Commission (FCC) at frequencies vidual LEDs, but then use those data to rate the entire product corresponding to radio and television transmissions. life. (Labeling programs also use LM-80 test data.) In reality, The Institute of Electrical and Electronics Engineers a product has many more components than just the LED. (IEEE) sets voluntary standards for distortion of the voltage Electronic drivers with electrolytic capacitors are known to waveform in the utility supply to buildings (IEEE 519) in have a short life, especially at high temperatures. Products order to ensure that electrical and electronic equipment in the claiming a life of 25,000 to 50,000 hours may not live up to building has a reasonably clean supply of power (correct such claims as a result. LM-80 test results are more appro- frequency, voltage, and lack of distortion). Distortion of priate for LED package manufacturers to provide to product the ­ inusoidal voltage waveform is of most concern and is s manufacturers, not to product end users. Even though white expressed in terms of a parameter known as “total harmonic papers have started to point out this issue (Next Generation distortion” (THD),10 which is typically limited to about Lighting Industry Alliance, 2011) and research is under way 5 percent. On the other hand, industry voluntary standards set to develop test procedures to predict whole product life more limits to the distortion in the current waveform drawn by the accurately (Davis, 2012; Lighting Research Center, 2012), equipment connected to the electric supply. The distortion is early adopters of LED lighting may be disappointed when products do not live up to the claims on their labels, based as 10 Total harmonic distortion (THD) of the supply voltage is equal to they are on LM-80 results. Some SSL product manufacturers the square root of the sum of the squares of the amplitudes of the volt- have started offering warranties for their products. This too age harmonic frequencies above 60 Hz divided by the amplitude of the is challenging because the terms and conditions for product fundamental 60 Hz voltage. A high THD (>33 percent) causes problems in replacement or cash reimbursement can be difficult to define three-phase power systems, because usually the dominant harmonic current and settle. is the third harmonic. The third harmonic currents add in the neutral wire Other examples of industry challenges with standards of the electrical system, and in cases of high THD one can have a situation where the current flowing in the neutral wire exceeds the rating of the wire, include the current color standards (e.g., ANSI C78.377) causing overheating.

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ASSESSMENT OF SOLID-STATE LIGHTING PRODUCTS 69 expressed as THD limits for the current, calculated in the same In the European Union, the Low Voltage Directive way as for the supply voltage; for commercial and industrial (2006/95/EC) of the European Parliament sets limits for PF, lighting equipment, the THD limit is set at approximately THD, and radio frequency emissions for lighting equipment 30 percent by ANSI standards. For fluorescent and HID and does so by reference to standards published by the Inter- lamp ballasts these limits are defined in ANSI C82.77-2002. national Electrotechnical Commission (IEC) and the Comité The displacement of the current waveform is expressed in International Spécial des Perturbations ­ adioélectriques R terms of PF, which is usually defined as the ratio of the real (CISPR; in English, Special International Committee on electric power flowing in the product to the apparent power.11 Radio Interference). All of these limits are mandatory in ANSI standards and other voluntary standards also define PF member countries, and the PF and THD limits tend to be limits for lighting equipment, typically 0.9 for commercial stricter in Europe (THD limits for current are in the range of and industrial equipment. These limits have been in place for 30 percent) than they are in the United States and apply to a several decades and, because of a lack of reported problems, broader class of lighting products, such as lighting controls. seem to be appropriately set. There are currently no THD or On the other hand, CISPR does not distinguish between PF standards for SSL products, so it would seem appropriate residential and non-residential emission limits, and the that similar limits be set for SSL drivers for commercial and European requirement falls between the FCC’s residential industrial applications as for fluorescent ballasts. It should and non-residential limits. Other countries typically follow be noted, however, that, for residential lamps with integral either the European model or the U.S. model. ballasts and medium screw bases, ANSI C82.77-2002 speci- Historically, there has been a tug of war between the elec- fies very loose standards—PF is required to be greater than tric utilities and the lighting industry about the importance 0.5 and THD less than 200 percent. Note, however, that the of stricter limits on power quality metrics, in particular on PF for an incandescent lamp is 1 (i.e., “perfect”) and its THD and PF, because of concerns about incompatibility THD is 0. Therefore, the impact of the residential standard between an increasing number of electronic loads in build- has been minimal as the penetration of screw-base CFLs is ings. However, the reported number of incidents claiming limited. As LED lamps become more ubiquitous as replace- poor performance because of power quality problems has ments for discontinued incandescent lamps, the effects of the remained low, while the number of installed electronic bal- liberal PF and THD limits may not be so benign. The ANSI lasts has increased. Electronic ballasts, introduced to the standard for residential screw-base lamps should match that market in the 1980s, now account for more than 80 percent of commercial and industrial applications, as for fluorescent of sales of all linear fluorescent lamp ballasts in the United ballasts. States. The current limits, therefore, appear to be appropriate. Modern lighting equipment, such as electronic ballasts for fluorescent lighting or drivers for SSL devices, also generate FINDING: There are existing standards for THD and some electrical energy in the radio frequency bands. These PF for electronic ballasts for linear fluorescent lamps, but types of equipment are termed unintentional radiators by the at present there are no such residential standards for LED FCC, and the FCC sets limits for the conducted (i.e., along d ­ rivers that are external to the lamp. Standards for low- the electrical wires) and radiated (i.e., into the air) emissions wattage, integrally ballasted CFLs with medium screw bases of such equipment.12 Separate limits are set for residential in residential applications allow low PF and high THD. and non-residential applications, with the residential limits being significantly stricter than non-residential ones, pre- RECOMMENDATION 4-5: For external solid-state sumably to protect the consumer’s ability to receive AM lighting drivers in general, industry should adopt the same radio broadcasts in the home. total harmonic distortion and power factor standards that are in place for electronic ballasts for linear fluorescent lamps. Industry should revisit the standards for low-wattage medium 11 The power factor (PF) of the equipment is equal to the electric power screw-base lamps to determine their impact on power qual- dissipated in the equipment expressed in watts divided by the product of ity before applying them for light-emitting diode lamps, the amplitude of the supply voltage and the amplitude of the electric cur- rent drawn by the equipment expressed in volt-amperes. In the past when and these standards should match those for commercial and most ballasts used in lighting were magnetic coils, the main effect to reduce industrial applications. PF came from the phase angle difference between the supply voltage and the current drawn by the equipment, which is why PF can be thought of as the displacement of the current relative to the voltage. With modern SSL PRODUCT COSTS electronic ballasts this effect is smaller, and increasing THD also decreases PF. For example, in the absence of any displacement PF, a THD of about A recent limited survey of consumer prices for a variety 44 percent corresponds to a PF of 0.9. of lamp types (A19, MR16, PAR20, and PAR38) at a Home PF is of particular interest to the electric utilities because they bill their Depot store in New Jersey indicates that the initial cost of customers based on delivered real power. However, the transmission line LED lamps ranges from 3.5 times to 15 times (PAR38) capacity is expressed in terms of amperes of current, so a low PF product that of halogen lamps (PAR20). However, when the total will limit the utility’s ability to generate revenue. 12 47 CFR Part 15 and 47 CFR Part 18. cost of ownership is calculated using an electricity rate of

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70 ASSESSMENT OF ADVANCED SOLID-STATE LIGHTING TABLE 4.1 Consumer Prices for a Variety of Lamps—Incumbent and Likely LED Replacement Halogen Incandescent LED Summary Price Price (incl. 7 (incl. 7 Savings Initial Lamp Power percent Life Cost to 10,000 hr Power percent Cost to 10,000 hr Over Savings Cost Type (W) sales tax) (h) Owna Costb (W) sales tax) Life (h) Owna Costb 10,000 hrs (%) Ratio A19 43 $1.75 1,000 $6.48 $64.85 12 $16.02 10,000 $29.22 $29.22 $35.63 55 9.1 MR16 50 $6.66 2,000 $17.66 $88.28 10 $26.72 10,000 $37.72 $37.72 $50.56 57 4.0 PAR20 50 $6.76 3,000 $23.26 $77.54 8 $23.51 10,000 $32.31 $32.31 $45.23 58 3.5 PAR38 90 $3.83 2,000 $23.63 $118.15 18 $56.68 10,000 $76.48 $76.48 $41.68 35 14.8 T3 150 $4.42 2,000 $37.42 $187.10 not available not applicable a Energy rate $0.11/kWh. b Not including labor to install lamp(s). $0.11/kWh, LED lamps save between 35 and 58 percent meet the needs of desired tasks or ambiance for the occupant. over 10,000 hours of operation, which corresponds to about Responding to this opportunity, researchers and industry 10 years in typical residential use. Table 4.1 summarizes the groups have been attracted to the concept of creating mini results of this survey. The LEDs that were chosen for this direct current (dc) grids within buildings for lighting and comparison are the closest available in light output to the some appliances (as well as power production from photo­ halogen lamps that they would replace. The “cost to own” is voltaic systems) while maintaining an alternating current the price of the lamp plus the energy cost over the lifetime (ac) power grid to transmit power from the generation site of the lamp. This calculation is limited to 10,000 hours, even to end-user sites without much loss (EMerge Alliance, 2012; though most of the life ratings shown on the LED packag- Narendran, 2012; Thomas et al., 2012). ing are actually longer than that. The initial price ratio in A dc-powered SSL infrastructure that allows for rapid the final column is just the ratio of the prices of one LED to reconfigurations of lighting systems using LED-lighted one halogen lamp (measuring “sticker shock”) even though ­panels that snap in and out of a modular electrical grid, makes more than one halogen lamp needs to be purchased to reach it as easy to redesign lighting as to move furniture, provid- 10,000 hours of use. Finally, it is also worth noting that LED ing value to the end users. Such concepts not only allow for alternatives are not available for all lamp types at this time, greater energy savings, but also can improve lighting in our such as the T3 tubular lamp that is used for example in some built environments. bathroom vanity lights and floor lamps. A calculation of life- cycle costs of LEDs and various fluorescent lamps, taking FINDING: The power requirements and flexible physical account of discount factors and expected improvements in configurations of SSL make attractive the concept of a new LED performance, is included in Chapter 6. dc building lighting infrastructure. RECOMMENDATION 4-6: The SSL industry should FUTURE OPPORTUNITIES collaborate with other industries such as building materials Purchasing a product while the technology is still evolv- and construction to explore the challenges and potential ing is always challenging, especially when the life of the benefits of developing and adopting standards for a new dc product is very long. Having said that, people are now electrical infrastructure. accustomed to upgrading computers and cell phones in 2 to 5 years because they see value in the new product’s functions. REFERENCES The same cannot be said for lighting. Until now, people have typically changed a light bulb only when the previous one has Acikalin, T., S.V. Garimella, A. Raman, and J. Petrosk. 2007. Charac- terization and optimization of the thermal performance of miniature failed. Unless the payback period is very short, many would piezoelectric fans. International Journal of Heat and Fluid Flow find it difficult to justify investing in LED lighting products 28(4):806-820. as replacements for traditional light bulbs, as promoted by Davis, J.L. 2012. Building a System Reliability Model for SSL Luminaires. the SSL industry. As a result consumers take a “wait and see” Paper presented at The Seventh Annual DOE Solid-State Lighting approach, even though the currently available LED products M ­ arket Introduction Workshop, Pittsburgh, Pa., July 17-19. DOE (U.S. Department of Energy). 2012. CALiPER Program. Available could save them significant amounts of energy. at http://www1.eere.energy.gov/buildings/ssl/caliper.html. Accessed Nevertheless, SSL offers new methods to light our spaces. August 2, 2012. SSL technologies can be embedded into many types of architectural elements due to their small size and long life to

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