Municipal lighting is an enormous market for LEDs. Most US cities have installed at least some LED street lamps, and a small number have switched over almost entirely. LEDs are considered superior for street lighting for several reasons, but their appeal was dimmed (sorry, couldn’t help myself) in 2016 when the American Medical Association (AMA) warned that some LEDs have adverse effects on night driving and human health. Lighting experts and cities interested in LED street lighting have been contending with that warning ever since.

The AMA cautioned that high-intensity LED lighting was bad for night-time driving because the illumination produced in the part of the spectrum that appears white to the naked eye (in the blue frequencies) is too intense. It would be perceived as glare that could affect driving. Furthermore, AMA said these frequencies of light suppress melatonin in humans, which the organization linked to problems with sleeplessness, reduced daytime productivity, and even obesity.

The AMA recommended minimizing output in the blue part of the spectrum and including shielding against glare. The figure of merit when discussing the appearance of a light source is correlated color temperature (CCT), which is expressed in degrees Kelvin. Most of the LED street lights that get installed are rated at a CCT of between 3,000 K and 4,000 K. The AMA suggested light fixtures should be 3,000 K or lower for roadway installations due to the effects of blue lighting.

The Municipal Solid-State Street Lighting Consortium (MSSLC), a program within the US Department of Energy (DOE), has been the point source for the responses to the concerns raised by the AMA. The MSSLC contends that CCT is not the only factor to consider when measuring what’s referred to as the melanopic output of LED lighting.

That’s a word that pops up constantly in discussions about LED street lighting. It’s either so new or so esoteric it isn’t in major dictionaries. Melanopsin is a photopigment – a protein – found in the retina; it has a direct relationship with circadian rhythms. Melanopic describes how certain kinds of light might affect human sleep cycles via activation of melanopsin. The illumination from LED street lights qualifies.

So back to the MSSLC. It says that any evaluation of melanopic output of LED street lighting has to take into account a number of factors beyond CCT, including luminaire output, fixture type/distribution, and lighting design. Lighting engineers can balance these factors to design LEDs with higher CCT levels but still reduce the melanopic output as recommended by the AMA.

Portland OR began swapping out its sodium street lights before the AMA issued its warning, and continued doing so afterward. The city has approximately 45,000 street lights and almost all of them are now LEDs, and most of those are 4,000 K lamps. Decorative lights (in city parks, for example) are all 3,000 K. The Portland Bureau of Transportation's (PBOT) FAQ about the new lighting on Portland’s municipal web site addresses the AMA warning at length, including copious links to additional information. Many Portlanders tend to be absolutist about health warnings.

Cities are beginning to replace sodium street lamps, with their familiar yellow-orange glow, with LED lighting. The new LED lights are more efficient, and life cycle costs are already lower. This is Route 26 (Powell Blvd.) in Portland OR, which has installed LEDs in nearly all of its 45,000 street lamps. Source: EDN

Other cities that have replaced the majority of the sodium lights with LEDs include Boston, Los Angeles, and Seattle. In other American cities, the vast majority of street lights are still high pressure sodium (HPS) lights, however. Sodium lights are recognizable by their distinctive yellow-orange glow. They became attractive for street lighting because they are far more efficient than incandescents and fluorescents.

On the downside, Portland found that with HSP street lights, too much light ends up focused at the base of the poles they’re mounted on, while not enough fills the space between poles. Sodium light is also monochromatic; the result is color distortion that some people reportedly find difficult to handle. Also, disposal of sodium lights is difficult because they contain mercury.

LEDs promise to lower maintenance costs, lower energy costs, and last longer than all of the other choices for municipal lighting, however. PBOT said it had to replace its old sodium lights every 5 years; the new LEDs are expected to last for 24.

The prices for LED lights have been steadily falling, and are expected to diminish further. PBOT said the cost of the specific make and model of LED fixture it has been installing (the Leotek ECobra) started at $500 per in 2000, but by 2018 it had dropped to $124 each.

HPS lights are still cheaper at $110 apiece, so a city replacing 50,000 lights with LEDs will face an upfront additional cost of $700,000. Municipalities are forever scrambling for money and that’s not chump change even for a large city.

But even though HPSs are less expensive to buy, just given their longer life spans, LEDs are already far more economical in the long run. A city with HPSs would have two more rounds of outlays for replacements before a city with LEDs would have to do the same. Also, as PBOT reports, “[B]ecause LEDs last longer and are easier to service, the City projects a 75 percent reduction in maintenance costs over the life of the LEDs.”

The new lights draw 29W each, whereas the replaced sodium lights were 118W. Advocates also assert that the light from LED street lamps reflects less than the illumination from sodium lights, minimizing light pollution.

Assuming the engineering claims about LEDs are accurate, even at a slightly higher upfront cost, LEDs are already the better economic choice for municipal street lighting. Even if the AMA’s worst fears about LED street lamp illumination are proven, the economics of LED street lighting are getting too attractive and may trump health concerns. It seems inevitable that the yellow-orange glow associated with urban living will eventually be just a memory.

For any municipal engineers looking to get additional information, the MSSLC is the main source, including engineering data on the many types of illumination. The DOE set up the MSSLC in 2014 to help support cities considering the use of LEDs. Operating out of the DOE’s Office of Energy Efficiency & Renewable Energy, the MSSLC “represents a coordinated effort among interested cities, power providers, government entities and others to minimize duplication of effort and spread associated risk across multiple locations.” It’s essentially a user group backed by DOE resources.

Those “resources” are mostly a knowledge base. By federal standards, the consortium has a paltry budget in the single-digit millions of dollars. That said, providing information about the technologies available and occasionally offering a modest grant is enough to get some cities started. Cities that want to consider installing LED lighting won’t have to start from scratch, and could benefit from the experience of others who have already adopted the technology.

EDN editor-in-chief Brian Santo has been writing about science and technology for over 30 years, covering cable networks, broadband, wireless, the Internet of things, T&M, semiconductors, consumer electronics, and more.