The color of nighttime is changing. It’s humans’ fault, and the change could have massive implications for animals and people alike.
How can the color of something as fundamental as nighttime change? To understand that — and why the change is happening — we need to take a step back and begin with some basics.
Lighting up the Night
Lighting city streets at night is tough. As early as the 1500s, Paris installed street lighting at scale. At the time they used candles and lanterns, which give off a tiny amount of light. Still, the effect was remarkable.
People felt safe from crime. They could stay out late, and stores could stay open past dark. The city flourished.
As people started to drive vehicles after dark, though, the dim light of candles and later gas lamps couldn’t keep up. Around the turn of the 20th century, electric lightbulbs helped, but their filaments still glowed too dimly to fully light dark streets.
In 1932, all that changed with the introduction of sodium vapor lamps. These lamps work by creating an electric arc in a bulb filled with vaporized sodium. They’re efficient and extremely bright. Some bulbs pump out 100 lumens per watt of power, which makes them way brighter than incandescent bulbs.
The issue — or perhaps, as we’ll see, the benefit — of sodium vapor lamps, though, is that they put out a single, monochromatic color. Sodium emits light at around 590 nanometers, and thus sodium vapor lamps do as well.
That makes their light a deep, unchanging yellow color.
The Color of Night
Picture a city street at night, lit by streetlights. Instinctively, you probably picture a road lit up by hazy pools of yellowish light, splashing and reflecting off asphalt, puddles, or wet pavement.
Indeed, that glow has long been a characteristic trait of urban nightscapes, making our night vision seem surreal, almost like looking through a vintage filter. However, our nights are shifting away from this particular hue, and our cities are beginning to tell a different color story.
And the culprit?
There’s a simple reason why the color of nighttime is changing: cities are replacing inefficient sodium vapor lamps with modern LEDs. And today’s LEDs simply look different.
For one thing, LEDs are a totally different color temperature. Most streetlight LEDS are tuned to mimic the color of daylight. Light color is measured in degrees Kelvin, with a lower number signifying a warmer, more orange light. A traditional sodium vapor lamp puts out light at around 2000K.
A modern streetlight LED? 4000–5000k. The upshot is that LED streetlights have a much bluer, more sunlight-esque hue. Think about the difference between the warm glow of a traditional incandescent bulb in your cozy living room (about 2700k) and the harsh, clinical glow of fluorescents in a hospital (5000k).
With the switch to LEDs, nighttime is becoming less like a living room, and more like a hospital.
Why Color Matters
That matters, and for reasons that go far beyond aesthetics. The light that LEDs emit is much more diffusive than yellow light, making our nights brighter and obscuring our view of the stars.
Astronomers are already feeling the pinch, with this increase in light pollution hampering their observations.
Then there are the impacts on human health and the environment to consider. Research suggests that exposure to blue light during the night can interfere with our circadian rhythms, potentially leading to sleep disorders and other health problems.
Wildlife, too, is affected. If you turn the nighttime into a daylight-colored, blueish dreamscape, it confuses nocturnal animals. This can disrupt their natural patterns of hunting, mating, and sleep. It can even reportedly lead to insect infestations, as bugs cluster around the bright, clear lights.
LEDs can also fail in spectacular ways. Some aging LED bulbs have recently begun turning purple. If you’re a barn owl trying to catch a mouse, try dealing with that!
Where to Go From Here
So, where does this leave us? It’s a tricky balance. LEDs are way more efficient than sodium vapor lamps. They use less power and need less maintenance.
But their multi-chromatic light — as well as their bright blue color — introduces its own array of problems.
As LED technology continues to evolve, there is hope. Scientists and conservationists are actively studying the effects of rapidly changing the color of nighttime. They’re also developing special LEDs that more closely mimic the light from lower-color-temperature sodium vapor lamps, while still shining brightly and efficiently.
Scientists are also working on filters for existing streetlights that help to remove some of their concerning wavelengths — especially those that tend to attract flying insects.
So, the next time you’re out on a city street after dark, take a moment to look up. Consider the color of the night, and think about what you want it to be. The color of our nighttime is changing, but maybe, just maybe, we can have some say in how it changes. The night belongs to all of us, after all.
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LED streetlights with a color temperature of 3000 deg K are readily available and do not have the problems that higher color temperature LED streetlights have. They are vastly more efficient than sodium vapor streetlights, and require vastly less maintenance.