Stars vanishing from view faster than previously thought

With help from international citizen scientists, a German research group has attempted to quantify the extent to which artificial lighting has caused stars to vanish from human view. In suggesting an alarming 60% decline over 18 years, the team implicates LEDs in more ways than one.

The researchers from the GFZ German Research Centre for Geosciences in Potsdam correlated star visibility with changes in sky brightness as measured by 51,351 individuals who used a template provided by Tucson, Arizona’s National Optical-Infrared Astronomy Research Laboratory, which is part of the U.S. government’s National Science Foundation.

The measurements took place between January 2011 and August 2022 and revealed an annual increase of 9.6% in sky brightness.

Brighter skies bleach out the visibility of stars, so the Potsdam group applied a set of algorithms and variables to extrapolate the extent to which stars are vanishing from view., as they reported in the journal Science.

“For an 18-year period (such as the duration of a human childhood), this rate of change would increase sky brightness by more than a factor of 4,” the team states in the paper lead by Christopher C.M. Kyba. “A location with 250 visible stars would see that number reduce to 100 visible stars over the same period. Because our method uses measurements made with human vision, it accounts for changes in both the radiance and spectrum of the night sky.”

Doing the math, that means that 60% of stars are fading from view every 18 years. The available data and citizenry was heavily weighted toward Europe, North America, and to some extent Japan. The rate would probably be higher if observations were available from other parts of the world, especially those experiencing rapid modernization, the paper notes, an insight which echoes a recent call from a Swedish/U.S. team for consistent methodologies for measuring light pollution and its many impacts (not just on star gazing).

But even 60% is a much more rigorous disappearing act than perhaps previously thought. Therein lies one reason to incriminate LEDs. The researchers note that earlier measurements of sky brightness taken from satellites have failed to capture blue spectra that can veer skywards from LED lighting. And, they note, blue light energy is particularly guilty at washing out the view of stars.

“In principle, it is possible to directly measure skyglow through satellite observations of Earth at night,” they write. “Unfortunately, the only satellite instruments that currently monitor the whole Earth have limited resolution and sensitivity and cannot detect light with wavelengths below 500 nm.”

The report does not mention the increase in blue spectra detected in another recent study of similar years in Europe by Britain’s University of Exeter. The Exeter study used images from the International Space Station, which orbits at a much lower altitude than most satellites, taken with digital SLR technology.

But the two studies corroborate that blue wavelengths are night sky culprits.

The German study ascribes blame not just to LED street lighting, but also to LED lighting for advertising and for architectural purposes. In fact, it notes that advertising and decorative lighting is more likely than street lighting to stretch horizontally, which can have a more harmful night-sky effect than vertically pointed streetlights. “[L]ight propagating toward the horizon is the largest contributor to skyglow because of its longer path length (by an order of magnitude) from ground to space at such angles,” the study authors explained.

Not all LED streetlights are created equally in that regard, though. The Tucson-based International Dark-Sky Association (IDA) issues a seal of approval for street luminaires that avoid spill and glare, such as those used in parts of England’s Lake District National Park.

Even properly pointed streetlights can be culpable night-sky villains in the general sense that the energy efficiency of LEDs has encouraged their adoption, making artificial lighting more widespread than in pre-LED days.

The German team stops short of concluding that is happening, but notes that “some researchers have predicted…a rebound effect in which the high luminous efficacy (more light emitted for a given power) of LEDs leads to more or brighter lights being installed or longer hours of operation.”

One group that has raised such concerns is the IDA, which is granting light monitors to certain qualified entities to help them measure light pollution.

The U.S.-based DesignLights Consortium (DLC) has also recently focused on promoting responsible uptake of energy-efficient LED lighting via its LUNA v1 Technical Requirements to help buyers, designers, and specifiers identify outdoor fixtures that mitigate excessive artificial light at night. DLC offers resources such as educational events and guidance for outdoor lighting based on lighting research (see sidebar on “Examining solutions for responsible outdoor lighting”).

MARK HALPER is a contributing editor for LEDs Magazine, and an energy, technology, and business journalist ([email protected]).

Examining solutions for responsible outdoor lighting

In collaboration with Honolulu Energy and the Illuminating Engineering Society’s Honolulu Section, the DesignLights Consortium will host a Feb. 1, 2023 panel discussion titled “Impacts of Outdoor Lighting: Considerations to Reduce Energy, Save Money and Minimize Light Pollution for People and the Environment.”

Panelists from DLC, Hawaii Energy, the U.S. Fish and Wildlife Service, and the University of Hawaii’s Institute of Astronomy intend to explore the effects of outdoor lighting on astronomical studies and coastal ecosystems. The mix of scientists, consultants, and regional program leaders will talk about challenges in outdoor lighting, explain sky glow and light trespass, and deliver guidance on how building owners, municipal authorities, and outdoor lighting stakeholders can decrease overlighting and minimize negative effects of nighttime illumination while enabling safety, visibility, and community engagement alongside energy savings.

Visit the DLC website for participant details and to register for the online event.

— Carrie Meadows

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