Darren Cassey 2 years ago 118
Wins

This Is Why Street Lights Are Orange

It's one of those things you might never have even considered, but there's a very simple reason why street lights emit orange light - and why white light is becoming more and more popular

Remind me later
"Highway 401 Night Lapse Busy" by kennymatic/Flickr

While researching a recent article on the evolution of headlights, I began reading about ‘selective yellow,’ which is the official name for yellow headlights. The reason they’re seen as advantageous is that they remove the blue to violet wavelengths from the projected light - human eyesight struggles to process these colours, which are the cause for dazzle and glare while driving in the rain and snow at night. By removing the blue-violet wavelengths and viewing the road in yellow light, you can see about 15 per cent less, but the effect of this isn’t so bad since the perceived quality of your vision is improved.

After reading that, I had a brainwave: that must be why streetlamps are orange! Well, no. Turns out there’s a difference between orange and yellow, who knew? After further research I discovered that the reason street lamps are yellow is actually far more simple than that: orange light is cheaper to produce.

Most street lighting comes in the form of high pressure sodium lamps, which produce the most amount of light for the least amount of electricity required to power them. The way it works is that the lamps have a quantity of sodium in them, and when electricity is passed through the sodium it gets excited and gives off an orange glow.

While this is good for your local council’s energy bills, it’s not ideal for people driving on the road or walking on the pavement. Studies have consistently shown that people perceive an orange-lit street as darker than a white-lit street, even when identical levels of luminance are provided. It’s also been shown that white light doubles a driver’s peripheral vision and reduces their braking times by 25 per cent when compared to sodium orange. That’s a huge difference.

So there you have it, street lamps are orange because they’re cheaper that way. The numerous disadvantages to people’s safety are the main reason why many towns and cities have been moving towards LEDs and high-intensity discharge lighting that provide a cleaner white light - new technologies mean white light doesn’t have to break the bank, and it could save a life or two.