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WP14 Street Lighting White Paper 20161201 ©2016 Lumileds Holding B.V. All rights reserved. White PaPer Street Lighting LEDs: coming soon to a street light near you The Performance, Design and Cost Benefits of Power LEDs in Street Lighting LEDs have been taking to the streets since the 1990s, when cities throughout the U.S. and Europe began replacing incandescent-based traffic lights with highly energy-efficient solid state fixtures. Today’s power LEDs are poised to cross the next municipal frontier and tackle the challenge of street lighting. If the mass adoption of solid state traffic signals is any indication, high pressure sodium, and high intensity discharge (mercury vapor) street lamps may soon lose their luster as the dominant sources of road and sidewalk illumination. The first LED street light installations are already being tested around the world, and in some cases implemented, in China, North America and Europe, as governments, municipalities and utilities strive to replicate the energy and maintenance savings of LED traffic lights elsewhere within their borders. With a 10- to 15-year lifetime that is at least triple that of current technologies, the maintenance advantages alone offer a street-smart argument for transitioning to LED-based systems. When we consider the design flexibility and sustainability af- forded by LED-based systems, the case for solid-state street lighting is compelling. LED solutions offer energy savings of as much as 50%, other ‘green’ features are mercury-free construction, and reduced light pollution made possible by the ability to precisely control light direction through LED placement and optics optimization. Moreover, street lamps using today’s power LEDs are fully capable of meeting stand- ard regulations for luminance levels and uniformity. LED solutions, unlike many other technologies, provide a sufficiently even light distribution (as shown in Figure 2) to meet recommended street light uniformity levels. This is a valuable benefit that is ca- pable of eliminating glare, hot spots and related visibility, safety and energy-wasting problems. Even light distribution improves the street lighting function and creates a better environment for people. All of these factors add up to make solid state street luminaires a bright idea.

collimating optic for maximum efficiency and uniformity. Figure 1. Solid-state street lamp demonstration design with LUXEON Rebel. over conventional light sources. priate but superior for many pedestrian and street lighting solutions. the 60,000-hour life expectancy of the LUXEON Rebel LEDs used in the model. tion of light through the optical lens.

up against the two dominant lighting technologies used for street lighting. Figure 2. Performance of LED demonstration design and conventional street lamps.

• Lower power consumption (67W) slashing energy use by 52% over Mercury Vapor (138W) and 26% over a high pressure sodium fixture (90W)
• Higher efficacy (50 lm/W) far exceeding mercury vapor’s 31 lm/W and again contributing to energy savings. – The higher efficacy measurement for high pressure sodium lamps is misleading because it includes wasted light that in turn wastes energy, as described below.
• More lux per watt (0.21) more than double that of a mercury vapor street lamp. – The LED-equivalent measurement for high pressure sodium lamps is skewed by hot spots that bump up the lux rating but cause undesirable visibility, safety and glare problems (see Figure 4).
• More even light distribution (0.40) than either of the other alternatives, as indicated by the ratio between the minimum and average lux produced in the target zone. The LED scenario was the only one of the three to match the European street lighting guidelines on this uniformity measure because of its ability to precisely direct light (see Figure 4).
• Longer lifetime (60,000 hours) translates into a 10- to 15-year life expectancy, depending on the duration of darkness in the specific geographic location. In contrast, conventional street lamps burn out after three to five years, incurring higher manpower and related maintenance costs for bulb replacement. Lower Total Cost of Ownership Beyond performance, one of the most compelling arguments in favor of LED street lamps is the cost advantage of operating and maintaining the fixtures. In part, this comes from reduced energy usage that can cut electricity bills in half. In part, it comes from the longer replacement cycle made possible by longer LED life. Increasing the interval between bulb replacements from three to five years to 10 or 15 means fewer truck runs, less fuel, and less overhead for work crews. This in turn accelerates the return on investment. Even with the higher initial cost of a solid state luminaire, municipalities can recoup the costs of an LED-based street lighting installation in four to six years (see Figure 3). The ROI will be even faster as power costs increase and technology advances increase LED light output, making it possible to deliver more lumens per watt for additional energy savings.

Figure 3. Estimated payback times. creates hot spots that can cause eye strain for drivers and pedestrians. ence between having a single massive spotlight pointed at a stage and aiming multiple smaller spots at strategic locations.

Figure 4. Light distribution of LEDs versus mercury vapor. expressed in the minimum/average lux ratio.

• Low Led power consumption yields energy savings of 20% to 50% over high pressure sodium and mercury vapor street luminaires at today’s levels, as indicated earlier. This energy efficiency is expected to increase with ongoing advances in solid state technology.
• LEDs’ ability to minimize wasted light lowers power demands even further by reducing the lumen requirements for a given street fixture. Since light distribution can be controlled on an LED-by-LED basis, engineers can effectively light the target zone without the light pollution created by a single-beam solution.
• Mercury-free LED construction makes solid state street lamps safe for landfills while also complying with mercury bans such as the European Union’s RoHS directive.
• Long LED life lengthens replacement cycles and associated fuel usage by maintenance crews, while also extending fixture life and thereby reducing the burden on the waste stream.
• LED street lights reduce pollution and carbon footprint via energy savings that lowers carbon dioxide and mercury emissions from coal-burning plants, as well as reduced fuel consumption by maintenance crews dispatched for bulb replacement.

WP14 Street Lighting White Paper 20161201 ©2016 Lumileds Holding B.V. All rights reserved. 6 Better Color Rendering and Color Temperature Choice Finally, LED street lights offer the benefit of more natural color rendering that can help improve safety and security. With a color rendering index (CRI) of 75, the LUXEON Rebel demonstration lamp discussed in this paper makes it easier for drivers and pedestrians to see street signs and other objects in the area illuminated by the fixture. To the extent that people feel safer and accidents can be prevented, the importance of the quality of light cannot be underestimated The availability of cool, neutral and warm white LEDs add the option to adjust the color temperature to the specific street lighting application. A neighborhood sidewalk might require a warmer color temperature, while a cooler LED might be used for roadway lighting to maximize efficiency. These alternatives are not available with conventional lighting technologies. Conclusion Taken together, these various solid state capabilities provide a persuasive value proposition for power LEDs in street lighting. As shown here, LED street lamps can meet standard regulations for luminance level and uniformity, deliver significant energy sav- ings, dramatically extend fixture lifetime, produce more usable light, support municipalities’ efforts to go green, lower the total of ownership, and more. Clearly, with so many incentives on the table, street lighting is a logical application for today’s increasingly powerful LEDs. The technology can help relieve government’s ever-present budgetary and environmental challenges as well as improve street light quality through features like reduced glare and better color rendering. LEDs have come of age for traffic signals, automotive light- ing and a host of other products. They now deserve serious consideration for roadway and pedestrian lighting.

©2016 Lumileds Holding B.V. All rights reserved. LUXEON is a registered trademark of the Lumileds Holding B.V. in the United States and other countries. lumileds.com Neither Lumileds Holding B.V. nor its affiliates shall be liable for any kind of loss of data or any other damages, direct, indirect or consequential, resulting from the use of the provided information and data. Although Lumileds Holding B.V. and/or its affiliates have attempted to provide the most accurate information and data, the materials and services information and data are provided “as is,” and neither Lumileds Holding B.V. nor its affiliates warrants or guarantees the contents and correctness of the provided information and data. Lumileds Holding B.V. and its affiliates reserve the right to make changes without notice. You as user agree to this disclaimer and user agreement with the download or use of the provided materials, information and data. WP14 Street Lighting White Paper 20161201 About Lumileds Lumileds is the global leader in light engine technology. The company develops, manufactures and distributes groundbreaking LEDs and automotive lighting products that shatter the status quo and help customers gain and maintain a competitive edge. With a rich history of industry “firsts,” Lumileds is uniquely positioned to deliver lighting advancements well into the future by maintaining an unwavering focus on quality, innovation and reliability. To learn more about our portfolio of light engines, visit lumileds.com.