LED street lamp cost measurement: is the time for a full outbreak?
For municipal lighting, LEDs promise to reduce maintenance and energy costs and outlast all other options. Even if the biggest fears of LED street lighting have been confirmed, the economics of LED street lighting are attractive, outweighing health concerns.
Municipal lighting is a huge market for LEDs. Most U.S. cities have installed at least some LED street lights, and a few cities have completely replaced LEDs. There are a number of reasons to choose LEDs for street lighting, but their appeal waned in 2016 when the American Medical Association (AMA) warned that some LED street lights could adversely affect nighttime driving and human health. Lighting experts and cities alike have been arguing over the warning ever since.
The AMA warns that high-intensity LED lighting is bad for nighttime driving because the blue part of the LED's white light spectrum is too intense. It creates glare and affects driving. In addition, the AMA says light at these frequencies suppresses melatonin in the body, causing problems such as insomnia, reduced daytime productivity, and even obesity.
The AMA recommends minimizing output in the blue part of the spectrum and increasing glare shielding. The figure of merit for the color appearance of a light source is the correlated color temperature (CCT), expressed in degrees Kelvin (K). Most installed LED street lights are rated between 3,000K and 4,000K CCT. Due to the effects of blue light, the AMA recommends that road-mounted luminaires should be no higher than 3,000K.
The Municipal Street Lighting Solid State Lighting Consortium (MSSLC), within the U.S. Department of Energy (DOE), has been an important source of responses to questions raised by the AMA. MSSLC believes that CCT is not the only consideration when measuring the melatonin output of LED lighting.
When discussing LED street lights, we can often see the new word melatonin. Melanosin is a photopigment in the retina that is directly related to circadian rhythms. Melatonin describes how certain kinds of light affect the human sleep cycle by activating melanopsin. LED street lighting is just right.
The MSSLC said that the evaluation of the melatonin output of LED street lights takes into account many factors beyond the CCT, including lighting output, luminaire type/distribution and lighting design. Lighting engineers can balance these factors and design LEDs with higher CCT levels, but lower the melatonin output to the range recommended by the AMA.
The city of Portland, Oregon, began replacing sodium street lights before the AMA's warning, and has continued since. The city has about 45,000 street lights, almost all of which are now LEDs, most of them 4,000K. Decorative lights (such as those in city parks) are all 3,000K. On the Portland Municipal website, the Portland Department of Transportation's (PBOT) FAQ on new lighting discusses the AMA warning in detail, including links to numerous additional information. Many Portlanders tend to take an absolutist stance on health warnings.
Many cities are beginning to replace the common yellow-orange sodium street lights with LED lighting. The new LED lamps are more efficient and life cycle costs have been reduced. Pictured here is Route 26 (Powell Avenue) in Portland, which has installed LEDs in nearly all of its 45,000 street lights. (Source: EDN)
Other cities that have replaced most of their sodium lamps with LEDs include Boston, Los Angeles and Seattle. However, in other U.S. cities, the vast majority of street lights are still high pressure sodium (HPS). Sodium lamps can be identified by their distinctive orange-yellow light. Such lamps are popular in street lighting because they are more efficient than incandescent and fluorescent lamps.
The downside, the City of Portland found, was that HSP street lights concentrated too much light on the bottom area of the poles and not enough to illuminate the space between the poles. Sodium lamps are also monochromatic, and color distortion is said to make it difficult for some people to deal with. In addition, sodium lamps are more difficult to dispose of due to their mercury content.
For municipal lighting, LEDs promise to reduce maintenance and energy costs and outlast all other options. PBOT says they have to replace the old sodium lamps every 5 years, while the new LEDs are expected to last 24 years.
The price of LED lights has been steadily decreasing and is expected to decrease further. PBOT said the cost of a particular make and model of LED fixtures they installed (Leotek ECobra), which cost $500 a unit in 2000, had dropped to $124 in 2018.
HPS lights are still cheaper at $110 each, so if a city were to replace 50,000 street lights with LEDs, it would cost an extra $700,000. So municipalities have been scrambling for funding, which is not a small amount even for a large city.
Even though the cost of purchasing HPS is lower, it will be much more economical in the long run to have longer LED lifespans. Cities with HPS will spend two extra rounds of replacement before cities with LED streetlights have to replace one round of streetlights. Additionally, as PBOT reports, “Given that LEDs last longer and are easier to service, the city expects to see a 75 percent reduction in maintenance costs over the life of an LED.”
The new street lamps consume 29W per lamp, while the replaced sodium lamps are 118W. Proponents of LEDs also assert that LED street lights reflect less light than sodium lamps, reducing light pollution.
Assuming the engineering claims about LEDs are correct, LEDs have become a better economical option for municipal road lighting, even with slightly higher upfront costs. Even if the AMA's biggest concerns about LED street lighting have been confirmed, the economics of LED street lighting are attractive, outweighing health concerns. It seems inevitable that the yellow-orange light that accompanies urban life will eventually become a memory.
MSSLC is a primary source for municipal engineers looking for more information, including engineering data for many lighting types. The U.S. Department of Energy established the MSSLC in 2014 to help cities consider LED street lights. Operating within the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy, the MSSLC "represents a coordinated effort among interested cities, power suppliers, government agencies, and other organizations to minimize duplication of effort and the associated risks expanded to multiple locations". It is essentially a user organization supported by resources from the U.S. Department of Energy.
These "resources" mainly refer to knowledge bases. By federal standards, the coalition's budget is only a few million dollars. That said, providing information about available technology, and occasionally modest grants, is enough to get some cities off the ground. Cities wanting to consider installing LED lighting don't have to start from scratch and can benefit from the experience of other cities that have already adopted the technology.
