The implementation of LED street lighting is rapidly moving from pilot projects to widespread use because of the promises the technology offers. Understanding those promises, including financial benefits, reduced carbon emissions and improved safety and security lighting, can be better achieved with a basic understanding of the technology and its functionality. Unfortunately, many articles and other research material either provide information overload or leave one with more questions that have been either asked or answered. This article is designed to provide a basic understanding of the technology, its features and benefits in street lighting use and through this knowledge to offer readers a level of confidence that LED lighting is the primary technology for this application
What is LED Street Lighting?
While LED technology for street lighting is relatively new, the science behind it is actually well understood because LEDs themselves have been around for decades. Basically, an LED is just a light bulb without the filament and its color and illumination intensity are dictated by the movement of electrons in the semiconductor material. And because LEDs are based on solid state technology, they can more readily be controlled and programmed which makes them one of the most versatile and flexible light sources available today.
LEDs used in quality street light luminaries are commonly referred to as High Power LEDs and are quite different from LEDs used in automobile brake lights or Christmas tree lights. The life span of an LED street light can exceed 50,000 hours, which is equivalent to almost six years of continuous operation which equates to 12 years of life when in operation 12 hours a day. To meet existing form factors, the mounting apparatus are available in conventional cobra head designs and, depending on the lighting application (i.e. freeway, residential street, parking lot, etc.), the LEDs are available in various wattages and with different color temperatures ranging from 3000K (warm white) to 6000K (day white). They are largely impervious to vibration and temperature extremes because they do not have filaments or glass enclosures that are subject to breakage. Among other functions, LEDs turn on at full brightness almost instantly, with no resart delay.
Rewriting the Standard for Street Lighting High and low pressure sodium lamps have been the de facto standard for street and security lighting for the past several decades but improved LED technology and lower prices have the potential to rewrite this standard in the not too distant future. A recent report by Pike Research (now a part of Navigant Consulting) predicts that LED street lights will become second in usage only to high pressure sodium lamps by the year 2015 with a continued upward curve toward predominance by 2020.
The following chart compares the efficacy of various street
|Technology||% Market Share||Typical Source Efficacy||Typical Efficiency||Typical Net Efficacy|
|59%||70 – 150||45%||32 – 68|
|10%||68 – 177||25%||17 – 44|
|Mercury Vapor||20%||34 – 58||30%||10 – 17|
|Metal Halide||5||61 – 85||35 – 40%||21 – 34|
|2||50 – 70||60%||30 – 42|
|Incandescent||4||10 – 17||60%||6 – 10|
|Induction||0||60 – 80||60 – 80%%||36 – 64|
|HE ceramic MH||0||95 – 120||60 -80%||57 – 96|
|LED||0||60 – 100||60 – 90%||36 – 90|
Source: Clinton Climate Initiative, 2010
System efficiency of high pressure sodium lamps is based on how many lumens actually reach the target area, not simply how many lumens are emitted from the lamp. However, the total efficiency of a street light system should consider both the efficacy (how efficiently electricity is converted to visible light) of the light source as well as the optical efficiency of the luminaire. Typically, 40% or more of the light emitted from a high pressure sodium lamp is trapped within the luminaire and does not reach the target area. A November, 2008 study in Oakland, California for street lighting in which installed LED street lights were compared to existing high pressure sodium lamps revealed the LED illumination as good or better even though measured Lumens per square meter (Lux) on the ground was less than for the high pressure sodium source.
In comparing basic design, LEDs don’t contain toxic chemicals like mercury which are found in traditional high pressure sodium lamps or mercury vapor lamps. Further, while high pressure sodium and other similar technologies continue to improve incrementally, LED technology is improving very rapidly in terms of luminous efficacy, color quality, optical design, thermal management, and cost. There is also considerable research suggesting that, especially at low light levels, humans have better visibility under the white light produced by LEDs than by the yellow light produced by high pressure sodium lamps.
The Need for a Lighting Revolution
Energy conservation and awareness created by new LED lighting technologies is also becoming a more predominant trend globally – and for good reason. In a report published by the International Energy Agency (IEA) (Light’s Labors Lost, 2006), lighting is responsible for 19% of global electricity use and around 6%of global greenhouse gas emissions. This information was further updated in an IEA 2011 report stating that doubling lighting efficiency globally would have a climate impact equivalent to eliminating half the emissions of all electricity and heat production in the EU. Published data from market intelligence and the IEA also suggests that in the United States alone, cutting the energy used by lighting by 40%would save US$53 billion in annual energy costs, and reduce energy demand equivalent to 198 mid-size power stations.
Narrowing the focus to how LED technology has the potential to affect energy usage in street lighting in the United States, current estimates show that there are about 52.6 million installed public roadway lights nationwide, which includes 26.5 million streetlights and 26.1 million highway lights. The U.S. Department of Energy’s Municipal Solid-State Street Lighting Consortium estimates the nation’s streetlights consume the energy equivalent of 1.9 million households and cost $6-8 billion annually for energy and maintenance.
According to one estimate, converting all of these streetlights to LEDs would halve the amount of energy used for lighting in the country. The impact of this data was significant enough to prompt the U.S. Conference of Mayors in 2012 to adopt a resolution endorsing the nationwide use of LED street lighting.
LED Lighting Technology Leading the Revolution
LEDs have become the driving force in the evolution of street lighting. The combination of improved nighttime visibility and safety, reduced maintenance/operational costs, no toxic chemicals and a decrease in carbon emissions have made LED lighting systems a top consideration for municipalities and utility companies everywhere.
The Climate Group, a non-profit international organization committed to a low carbon future, has recently released the findings of a two and a half year study(Lighting the Clean Revolution: The Rise of LED Street Lighting and What it Means for Cities) which examined the use of LEDs in major cities. Piloting 15 separate schemes in 12 cities across the globe, including New York, London and Kolkata, the report found that in some cases, LED technology accounted for an 85 percent reduction in energy costs. The report also indicates that citizens of pilot cities prefer LED lighting, citing social and environmental benefits. In Kolkata, London, Sydney and Toronto, between 68 and 90 percent of respondents indicated that they approved of city-wide LED rollouts. The pilot projects were launched as part of the Clean Revolution campaign at the Rio+20 UN Global Compact Corporate Sustainability Forum with the report generated by The Climate Group.
Across the United States, recent LED street light projects have been funded through the federal government’s stimulus programs as well as from the Department of Energy funding programs. Cities that have implemented LED street lighting systems either with government funding or through other means include Los Angeles, CA; Seattle, WA; Greenville, NC; Lima, OH; Madison,WI; Pittsburgh, PA; andWest Palm Beach, FL, among others.
While the advantages offered to these cities by implementing LED street lighting system are many, the most commonly cited are:
Overall System Cost – Across the country, most street lights have been in operation for more than 30 years on average. Many are over or undersized for current needs or the reason for their original installation may no longer exist. By transitioning to an LED street light system, municipalities can address these issues and in so doing increase the energy savings and decrease the energy bill.
Additional operational savings can be derived from: Long Life – with a projected lifespan of 50,000 hours and more, LED lighting systems contribute to reduced maintenance and replacement costs.
Lower Power Consumption – LED lights use less power than conventional street lights to produce more light. LED systems can also be powered by solar energy sources. Improved Power Usage – Many existing light fixtures emit only a fraction of the light actually produced by the source. LED lights waste less light and have a maximum power efficacy of 90 versus 68 for high pressure sodium lamps.
Smart Operational Control – Roadway lighting covers a broad range of locations, from low-traffic residential neighborhoods and rural roads to interstate freeway interchanges. All have their own requirements for acceptable light levels and distribution patterns and this is where LED street light systems with “smart control” can be the most effective.
For example, street lights with controls systems offer dynamic dimming during long periods of inactivity, a feature with tremendous potential to save energy, mitigate waste, reduce light pollution, and increase public safety. Or, LED street light systems with embedded sensors can detect movement from pedestrians, cyclists and vehicles, anticipate their approach, and communicate the change in traffic to light poles downstream, increasing light output in a fluid and real-time response to travelers’ needs.
Quality of Life – Because of its capability for dynamic control, LED street lighting can address issues of dark sky and light pollution in residential areas during the long night time hours of inactivity. Alternately, where and when needed, LED’s near white light makes it feel like daytime which can significantly help in reducing criminal activity. The improved illumination can also improve safety for drivers, cyclists and pedestrians.
Operational Standards – As LED street lighting grows in popularity, it is supported with a growing set of lighting standards that can be applied to help ensure the product performs as specified. These standards, which cover aspects of glare, visibility, uniformity, color accuracy, light pollution, light consistency and more, provide the metrics to help municipalities in comparing available options.
Carbon Footprint – LED lights contain no toxic materials and are 100% recyclable. Because of their long life, they can significantly reduce landfills and bulb disposal costs compared to conventional street lights.
Because LED technology is advancing so rapidly, utility companies and municipalities may have concerns that systems purchased today will become obsolete or will not be compliant with future upgrades. Reputable manufacturers however are making their LED street light offerings future-proof by designing them with replaceable modules that can be swapped out as technology improves. As well, the Department of Energy’s model specification for roadway luminaires contains an optional clause that requires the luminaire/driver to be able to accept a control signal and dim for future control. Finally, once one community, utility or State successfully implements an LED street lighting system, it paves the way for others to follow.