I want you to stop what you are doing—reading this paper, perhaps—and look up at the sky. You probably see a bright blue expanse possibly dotted with white or gray clouds. Oops. Try again later, as we want a good look at the night sky! Can you count the stars overhead? If you live in or near a city or population hub, the answer is most likely yes. Light pollution floods the skyline, distant stars obscured behind the bright skyglow. Cities are filled with sources of artificial light at night (ALAN) due to light-emitting fixtures like streetposts, spotlights, and skyscrapers. This ALAN harms humans, fauna, and flora within miles of any bright city center (United Nations Office for Outer Space Affairs, 2021).

Modern technology has brought a new type of lightbulb from an expensive luxury to a commonplace light source. LEDs, light-emitting diodes, convert an electric current into a burst of photons, shedding light into its surroundings. These LEDs outperform other light source types hand over fist. The usage of a semiconductor to produce light instead of heating up a filament or gas saves heaps of energy by cutting out power inefficiencies from the warming of elements. A study to determine the optimal lighting system for Pakistan amid a power and energy crisis determined that LEDs use 85% less watts than standard incandescent bulbs to achieve the same level of luminance (Khan & Abas, 2011).

Saving 85% on power consumption for lighting could save billions of dollars annually if we transitioned public lamps over to LEDs. With billions on the line, why shouldn’t we convert over as quickly as possible? Simply put: up-front savings are not the only change this overhaul would bring. The introduction of LEDs brings with it a whole spectrum of issues. Another study was run, this one on the changes light retrofits would bring. The United States Department of Energy (USDOE) conducted a study in 2017 to gauge how the introduction of LEDs would affect night skyglow and found that skyglow “should be no worse than before, and may possibly improve, relative to the system being replaced” (Kinzey et al., 2017). Meanwhile, another study in 2014 argues the opposite, claiming that “high correlated color temperature LEDs and metal halide sources produce a visual brightness up to 8x brighter than low-pressure sodium and 3x brighter than high-pressure sodium when matched lumen-for-lumen” (Luginbuhl et al., 2014).

Hung et al. wanted to investigate the confusion on LEDs “improving or degrading the quality of the night sky” (Hung et al. 2021). To do so, they used data obtained from the United States National Park Service’s (NPS) Night Skies Program, measuring changes in sky brightness in Chelan County after a countywide lighting retrofit project. (Hung et al. 2021). The group used before and after images of the night sky from the NPS night sky camera system and satellite imagery from the Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership satellite. And what did all of this research determine? Light pollution got both better and worse! Hung et al. wrote “our measurements show that the post-retrofit skyglow became brighter and extended higher in the sky, but upward radiance, as measured by the day-night band radiometer, decreased” (Hung et al. 2021).

In an annoying turn of events, LEDs both improve and deter city skyglow. The better shielding on the luminaires (ceiling-mounted, white LEDs) help reduce the amount of light shined upwards while the shorter wavelengths (bluer light) emitted increased the scattering the photons undergo. Our sky looks blue midday due to the blue light beamed from the sun scattering when it hits water molecules in our atmosphere. Increasing the amount of blue light late at night leaves more light to scatter, increasing the skyglow more than the shielding dampens it. LED lighting, as it currently stands, brings a net negative effect against the night sky. If you want to see the stars at night, I encourage you to petition your local city council to install warmer lights such as low-temperature LED bulbs.

References

Hung, L. W., Anderson, S. J., Pipkin, A., & Fristrup, K. (2021). Changes in night sky brightness after a countywide LED retrofit. Journal of Environmental Management, 292, 112776. https://doi.org/10.1016/j.jenvman.2021.112776

Khan, N., & Abas, N. (2011). Comparative study of energy saving light sources. Renewable and Sustainable Energy Reviews, 15(1), 296–309. https://doi.org/10.1016/j.rser.2010.07.072

Kinzey, B. R., Perrin, T. E., Miller, N. J., Kocifaj, M., Aube, M., & Lamphar, H. A. (2017). An Investigation of LED Street Lighting’s Impact on Sky Glow. U.S. Department of Energy Office of Scientific and Technical Information. Published. https://doi.org/10.2172/1418092

Luginbuhl, C. B., Boley, P. A., & Davis, D. R. (2014). The impact of light source spectral power distribution on sky glow. Journal of Quantitative Spectroscopy and Radiative Transfer, 139, 21–26. https://doi.org/10.1016/j.jqsrt.2013.12.004

United Nations Office for Outer Space Affairs. (2021). Dark and Quiet Skies for Science and Society. United Nations.