Why the iconic orange glow of streetlights is vanishing from our night skies

Nature · Published 3 October 2026 Swipe more like this →

In short: For decades, the distinct yellow-orange hue of low-pressure sodium lamps defined urban nights. Prized for their extreme energy efficiency and ability to cut through fog, these lamps were once the gold standard for street lighting. Now, they are being phased out, leaving behind a legacy of science and cinema.

The low-pressure sodium (LPS) lamp operates by ionizing a mixture of neon and argon, which glows red before vaporizing metallic sodium to produce a nearly monochromatic yellow light at 589 nm. This specific wavelength is highly efficient, with some models reaching up to 206 lumens per watt. Because this light is near the peak sensitivity of the human eye, it provides excellent visibility for outdoor tasks like roadway illumination, even if it renders colors indistinguishable.

Beyond street lighting, the unique properties of LPS lamps enabled a specialized film technique known as the sodium vapor process. Between 1956 and 1990, studios like Disney used this method to create seamless visual effects. By using a special camera to record foreground and background elements on separate film spools, they could create masks that were often superior to early blue-screen technology, famously appearing in films like The Birds and Mary Poppins.

Despite their utility, LPS lamps are disappearing. Production ceased at the final major factory in Hamilton, Scotland, on December 31, 2019, due to falling demand. While high-pressure sodium (HPS) lamps—which use translucent alumina to withstand higher temperatures and provide a broader light spectrum—remain in use, the industry is shifting toward narrow-band amber LEDs. These modern alternatives mimic the spectral benefits of LPS, which were once preferred by astronomers to minimize light pollution and by coastal communities to protect sea turtle nesting beaches.

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