By Daniela Castleberg

Original article:

Evolution of Brightness and Color of the Night Sky in Madrid

José Robles, Jaime Zamorano, Sergio Pascual, Alejandro Sánchez de Miguel, Jesús Gallego, and Kevin J. Gaston

  Our skies are getting bluer, and that’s not during the daytime. The introduction of LEDs as replacements to high pressure sodium lights has increased the amount of blue light in our communities at night. From the years 2010 to 2020, José Robles from the Universidad Complutense de Madrid and his team investigated light pollution changes as well as the increase of blue light and presented their findings in the article, “Evolution of Brightness and Color of the Night Sky in Madrid.” In this study, multiple kinds of readings were taken every night to record different aspects of sky brightness and color spectrum. Previous studies on light pollution had focused primarily on the brightness of the sky, not researched the changes in color. In this new study however, they took measurements that were able to tell which wavelengths of light were present.

             What they found was interesting, and not far from what has been seen in a number of other cities. In the year 2015, Madrid changed more than 50,000 out of 250,000 streetlights to LEDs, and in the four years that followed, “the color index shifted considerably toward bluer skies.” [1] This conclusion is powerful because according to the International Dark Sky Association, “exposure to blue light at night is particularly harmful. Unfortunately, most LEDs used for outdoor lighting – as well as computer screens, TVs, and other electronic displays – create abundant blue light.” [2] This blue light sends cues to our body to block melatonin production, shifts our internal circadian clock and disrupts our entire routine.

             As if routine disruption wasn’t enough, according to the UN Bio-Environment report, “convincing studies have shown the ability of [light at night] to promote the growth progression and metabolism in human breast cancer xenografts.” [3] But this issue doesn’t just affect women because similar findings have been found with regards to prostate cancer. If you were looking for a sign to stop using your phone late at night, you’ve found it. The scary part is that minimizing phone use won’t even make much of a difference if more streetlights change to LEDs because then we will almost constantly be surrounded by blue light.

            After reading about all these consequences, you might be wondering why blue light is being used at all? Blue light is a consequence of white LEDs, and white LEDs are being used in streetlights because they are perceived to be more cost effective than the legacy high pressure sodium bulbs. However, as the researchers from Madrid point out, “the relevant savings are not due to the lamps’ energy efficiency but the dimming capabilities and the lower [upward light output ratio] of the LEDs compared to traditional lighting.” [4] The research team suggests simply reducing power to current sodium bulbs as a cost-effective alternative to LEDs, because even dimmed LEDs emit enough blue light to cause negative consequences on light pollution.

            After ten years of research, José Robles and his team found that the amount of blue light in the night sky in Madrid increased significantly after LEDs were introduced into street lighting. Light at night is not created equal with blue light being particularly harmful for light pollution and the health of humans and other animals. Despite these negative consequences, LEDs rich in blue light have been more commonly used around the world as replacements to older kinds of lights and will continue to do so until better solutions can be found.

[1] Robles, J., Zamorano, J., Pascual, S., Sánchez De Miguel, A., Gallego, J., & Gaston, K. J. (2021). Evolution of Brightness and Color of the Night Sky in Madrid. Remote Sensing, 13(8), 1511. https://doi.org/10.3390/rs13081511; p. 4, 23

[2] International Dark-Sky Association. (2021, July 2). Human Health. https://www.darksky.org/light-pollution/human-health/

[3] United Nations Office for Outer Space Affairs. (2021, January). Dark and Quiet Skies for Science and Society. United Nations; p. 98

[4] Robles. Evolution of Brightness and Color of the Night Sky in Madrid; p. 23

References

International Dark-Sky Association. (2021, July 2). Human Health.
https://www.darksky.org/light-pollution/human-health/

Robles, J., Zamorano, J., Pascual, S., Sánchez De Miguel, A., Gallego, J., & Gaston, K. J. (2021). Evolution of Brightness and Color of the Night Sky in Madrid. Remote Sensing, 13(8), 1511. https://doi.org/10.3390/rs13081511

United Nations Office for Outer Space Affairs. (2021, January). Dark and Quiet Skies for Science and Society. United Nations.
https://www.unoosa.org/oosa/en/ourwork/psa/schedule/2020/2020_dark_skies.html