Don’t Blame Street Lights for Light Pollution — New Stats Say It’s Your Neighbors

Terry McGowan, FIES, LC, retired director of Engineering at the American Lighting Association (ALA) and co-chair of the Technical Committee of the DarkSky Association, presented the latest findings from the DarkSky Association to the ALA Engineering Committee last week.

“When it comes to residential lighting and dark skies, there is some new information that I want to bring everyone up to date on,” McGowan said, adding, “It’s a time of change.”  

McGowan explained that early on when DarkSky and like-minded groups were evaluating the effect of lighting on the night sky, high-pressure sodium – with its widespread yellowish cast – was the predominant light source for suburban and city streetlights, highways, and commercial buildings. The gradual conversion to LED lighting – which has a more cool blue appearance – reduced that overall haze of yellow to a large degree and kept the lighting more tightly focused onto the areas it was meant to illuminate due to the directional nature of LEDs.

The result is that the commercial sector has been able to get light pollution more under control. “There’s still a long way to go, but residential [use] has turned out to be more of an addition to sky glow than we had previously thought and now the focus is on residential outdoor lighting and the [circadian] disruptions it can cause,” he stated.  “We [DarkSky Association] have found that a lot depends on the type of lighting used, as well as the type of light source, and so there are going to be some changes.”

McGowan shared an image of Chicago’s downtown in the era of high-pressure sodium lighting, followed by a recent image where LED illumination in the same area has dramatically cut down on sky glow.

There is still room for improvement, however. “While LEDs have been good overall for shielding light pollution, the blue wavelengths from LEDs are still a problem,” McGowan stated. “The point is that it is not just street lighting anymore that contributes to the sky; residential lighting has gained importance. The world has become brighter — whether it comes from  a streetlight or from somebody’s window. We are losing our darkness, and when we lose our darkness, we lose a lot of things,” he remarked. “Visible light pollution has turned out to be an environmental concern, as it affects all living things — from animals to birds to insects. As the general public has become more aware, we have many more organizations and people who are saying, ‘It’s time to do something.’” In response, DarkSky International put out a simple consumer guideline a few years ago that provided the basic tenets of what homeowners need to look for when buying and installing outdoor lighting.

According to McGowan, this topic should become more important to lighting showrooms and manufacturers since a 2023 study has indicated that residential lighting is contributing more to light pollution year over year. There is another key point to keep in mind: It isn’t just the outdoor lighting on homes that is contributing to the problem, but also the light emanating from inside the home via floor-to-ceiling windows and skylights that spill out past the home’s exterior. “Light emitted from windows makes up a significant part of sky glow, so perhaps that is a business opportunity for showrooms that sell motorized shades and window coverings that can limit the [light spill] to some degree,” he commented.

McGowan explained that offering DarkSky-compliant outdoor fixtures does not mean the consumer will have less light for pedestrian safety on walkways or on porch stairs. “It involves shielding the light source in some way that minimizes light trespass into nearby homes, directs the light to where it’s neededt, and reduces glare, which is a problem with LEDs more  than with any other light source the industry has ever used,” he said.

Common rules of thumb for DarkSky’s newest guidance for compliance includes:

•  Shielding, plus the ability to dim or change the intensity or the timing of the lights can make a big difference, according to McGowan.

• Light output is limited to 1,000 lumens. “This covers most of the outdoor lighting that we tend to use for lighting, whether at the door, the porch ceiling, or other common places. Uplight in the 90- to 80-degree range will be limited. “It’s realistic to have some spill light,” McGowan said, adding, “There is a clause in the DarkSky recommendation to be able to do that.”

• Color temperature should be 3000K or less. “You can vary it if you feel that it should be warmer, or a bit cooler, over part of the evening. Just don’t go over 3000K.  You do need a standard photometric to be officially DarkSky-compliant,” McGowan stated.

“This topic is going to become more important, and it could become more of a marketing opportunity for ALA and ALA-member manufacturers and showrooms,” he said. “This is not strictly a U.S. certification, it applies all over the world. DarkSky has 70 chapters worldwide in 30 countries and about 993,000 supporters and members and advocates who work with us from a variety of organizations in order to move this whole idea along.”

McGowan concluded his presentation to the Engineering Committee by stating, “What we have here is an opportunity for ALA members — especially from a fixture standpoint as a way to reduce the amount of light that causes sky glow and from the standpoint of caring about the environmental effects that stray light causes.”  

Lighting News Now asked whether there is a national dark sky-friendly standard for all municipalities to follow or if it will remain up to the discretion of each city and state to decide — an aspect that has been a stumbling block for achieving nationwide adoption. McGowan answered that the goal is to get the DarkSky language to the point where it can be used and adopted by various cities and other organizations that decide local ordinances.

“I think this will still be a local [decision], but we wish that more cities will find the DarkSky [guidelines] easy to adopt,” McGowan said. “For example, DarkSky spent time recently working up the [lighting] language for seaports. The ports organization came to [DarkSky] and said they’d like to have dark sky lighting for ports, which have a lot of stray light, of course, because the lights are on at all hours of the day and night. The ports  organization adopted DarkSky’s verbiage and suggestions and passed official DarkSky certification. “I think we have a chance to create language that is understandable by municipalities to adopt going forward. I think it will be better [than what is in place currently], but it won’t be perfect.”

At Lightovation in January and June, more manufacturers were displaying what they label “dark sky-friendly” fixtures that meet most of the criteria set by the DarkSky Association, but without the official designation (said to be a cost-saving measure). Look for this category to grow on the manufacturer level as well as among consumers as awareness gathers momentum. 

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