Taking Inventory

In late 2014, the U.S. Department of Energy’s(DOE) Municipal Solid-State Street Lighting Consortium (MSSLC) published the results of a survey of entities across the United States that operate public street and area lighting.

Not surprisingly, the survey found that high-pressure sodium (HPS) is the most popular outdoor light source technology among respondents, followed by metal halide (MH). 

The light-emitting diode (LED) is now the third-most prominent source technology in terms of number of entities reporting use. While many muncipalities are embracing the benefits of LEDs, others are continuing to operate older source technologies such as mercury vapor. A significant number of organizations are planning to install advanced lighting control systems.

The survey was conducted in the latter half of 2013 to gain a better understanding of national energy consumption related to outdoor lighting used to illuminate public buildings and streets. Streetlights are of particular interest. An estimated 26.5 million streetlights are in service, and they impose an estimated annual electricity cost of $2 billion.

Some 245 entities participated, including 148 municipalities, 14 counties, 34 state departments of transportation, 17 investor-owned utilities and 32 municipally owned utilities. Combined, the municipalities and investor-owned utilities covered about 100 million people, including 25 percent of the total 2010 U.S. municipal population. The total public street and area lighting inventory for all respondents was 11 million luminaires, which consumed 5.7 billion kilowatt-hours.

Respondents identified HPS as the most widely used source technology for public street and area lighting; 86 percent indicated some use of HPS, and 82 percent cited it as the most prominent technology in their system. MH came in second, with 51 percent reporting some use. However, only 3 percent cited it as the most prominent technology, and 14 percent cited it as the second-most prominent. LED came in third, with 62 percent reporting some use of the technology. Eight percent cited it as the most prominent, and 30 percent of respondents cited it as the second-most prominent technology in their system. Respondents also indicated some use of mercury vapor (36 percent), induction (19 percent), incandescent/halogen (16 percent), fluorescent (11 percent), low-pressure sodium (8 percent) and light-emitting plasma (1 percent).

The average age of luminaires was 15.3 years. The average luminaire costs $96 per year in electric energy and $75 in operations and maintenance.

Many respondents reported continuing use of obsolete technology, notably mercury vapor. Fifty-three percent of investor-owned utilities indicated use of mercury vapor, which comprised 9.6 percent of their total inventory of 6.85 million luminaires. Thirty-two percent of municipalities also indicated use of mercury vapor, which comprised 6.9 percent of their inventory of 1.7 million luminaires.

These statistics suggest a significant opportunity to save energy, particularly through deployment of LED luminaires, which have come a long way in a short time and for which outdoor lighting was an early adoption opportunity. Replacing conventional technology with LEDs often presents 50-plus percent energy savings; according to the DOE, total savings can reduce a city’s electric budget by as much as one-fourth. Additional cost savings are realized in maintenance due to the longevity of the LED source. According to the DOE, a simple payback of 6–9 years is typical, based on projected energy and maintenance cost savings; this figure is improving over time.

As a result, the DOE has forecast significant adoption of LEDs through 2030, with the most rapid growth in street and roadway lighting. The DOE predicts LEDs will achieve an 83 percent market share of sales (measured in lumen-hours) by 2020 and nearly 100 percent by 2030. 

The most significant trends in LED street and area lighting have been increasing efficacy and decreasing cost. Between 2005 and 2013, package efficacy increased an average 8 percent annually. Meanwhile, package cost fell 36 percent during that same period, which, along with other factors such as volume and competition, has driven reduction in luminaire pricing. Seattle, for example, discovered a 50 percent price reduction in LED streetlights in just two years. Some manufacturers now offer residential LED streetlights for less than $200. 

LED technology is also an enabling lighting control functionality, such as shutoff and dimming. Advanced control options are now available coincident with a general move toward smart grids and intelligent highway systems. These systems can enhance energy savings and maintenance through luminaire remote monitoring and diagnostics. While the large majority of the 11 million outdoor luminaires included in the DOE study were controlled by a photocell controller and few by a centralized or advanced lighting control system, roughtly one-fourth of respondents (23.4 percent) said they planned to install an advanced control system within five years.

The MSSLC is working toward extrapolating the reported data to create an estimate of the larger national inventory. For more information, visit www.ssl.energy.gov and click on the Municipal Solid-State Street Lighting Consortium link.

About the Author

Craig DiLouie

Lighting Columnist
Craig DiLouie, L.C., is a journalist and educator specializing in the lighting industry. Learn more at ZINGinc.com and LightNOWblog.com .​

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