Carnegie Mellon University

streetlights and stars

The Challenge of Turning Down the Lights to Turn Up the Stars

Light pollution is a problem familiar to most residents of the eastern side of the country. Researchers at Carnegie Mellon have teamed up with the City of Pittsburgh to install special types of LED streetlights so that the stars can emerge once again.

LEDs have become a longer-lasting and more energy efficient alternative to incandescent bulbs. This fact has caused cities to prematurely transfer to these types of lights to illuminate the city streets. There was backlash from residents living in areas with bright new LED streetlights, and these complaints were compounded by researchers determining that the new bulb type causes significant glare to drivers. 

A 2016 report by the American Medical Association found that one of the main disadvantages of LED technology is the color temperature of the lights, which are measured in Kelvin. Higher-Kelvin lights emit light at a shorter wavelength. Original streetlights were made of High-Pressure Sodium (HPS) which gave it the iconic golden glow that most people are familiar with. However, the color temperature of many of those first-generation LEDs installed in cities was around 4,000K, which is squarely in the blue end of the spectrum. These incredibly bright bulbs are a challenge for drivers’ eyes to adapt to quick brightness changes in the dark. 

Pittsburgh’s relative cautiousness in replacing the remainder of its streetlights means that it can now choose streetlighting that’s more friendly to the human eye. Although the exact type of lighting that will be installed is not yet known, the LED lighting market has evolved over the past few years such that lower-color temperature LEDs are now available to purchase at a commercial scale.

Carnegie Mellon faculty members Diane Turnshek and Stephen Quick, and members of IDA Pittsburgh, are developing a comprehensive light pollution map of the city. The two maps - one from before installation of these new bulbs and one from after - will provide a concrete measure of how levels of light pollution are impacted by LED adoption and will highlight the city’s biggest light pollution offenders.

To learn more about this project, click here.