Here’s a question you may have asked yourself many times but possibly not enough to go and find the answer. Why are most street lights orange rather than white?
Well, I thought I had the answer when I noticed that cars tend to have a yellow tint to their headlights. Halogen lights, as used in most cars for the last 40 years, burn with a slight yellow colour, which removes the blue-violet wavelengths from the projected light. Blue and violet light causes dazzle and glare.
You might recognise this when cars with xenon headlights are first switched on – the lights have a blueish tint until they warm up when they become much whiter. By removing blue-violet wavelengths, the quality of our vision is actually improved even though the overall brightness is somewhat reduced.
So if that’s true for cars, then surely that explain why street lights are orange? No – silly me. It turns out there’s a big difference between orange light and yellow light.
But let’s go back to the beginning.
The first electric street lights appear
Electric street lights have a long history dating back to the 1800s. The first electric street lights were developed by Russian-born Pavel Yablochkov in 1875, replacing existing gas- or oil-lit lighting. These were known as ‘Electric Candles’, or ‘Yablochkov Candles’ and were, in fact, carbon arc lamps that used an alternating current to ensure that both electrodes were used in equal parts. Before long, these inefficient types of light bulb were replaced with incandescent lights, much like the ones we still use today.
Electric street lights first came to the UK in 1878, when electrical arc lamps were installed along the Holborn Viaduct and Thames Embankment in London. The first street to be lit with modern electricity as we know it was the appropriately-named Electric Avenue in Brixton in 1880.
Initially called lightpoles, then lamp posts and then street lamps, these raised lights used on the edge of roads or pedestrian footpaths have now become an everyday part of modern day living. Many of today’s street lamps have light-sensitive photocells that automatically operate as and when light is needed. As the sky darkens, the lights come on and as dawn approaches and the sky brightens, the lights go off.
Orange light is actually not that helpful for our eyes
Municipal authorities worldwide eventually began to adopt sodium lamps, and these burn with that familiar orange glow when electricity is passed through them. High-pressure sodium lamps are still used around the world for street lights because they produce the greatest amount of light for the least amount of electricity required to power them. They’re not the best lights and don’t light up a street as well as other lights. They’re just cheap to run because they use less electricity.
Research has revealed that our eyes perceive an orange-lit street as darker than a white-lit street even when the same levels of light are provided. In fact, white light actually increases our peripheral vision by 100% and reduces our braking times by 25%, when compared to orange sodium lights. That’s a very big difference. So, forget what’s best for drivers, street lamps are orange not because they help us see better but because they’re cheaper to run.
New technology can make street lights whiter, brighter and cheaper
Having said that, many towns and cities around the world have started moving towards LED street lighting and high-intensity discharge lighting, which provides a cleaner white light which helps us to see better. And, thankfully, these types of light don’t cost a lot to power.
A comparison between metal halide and high-pressure sodium lamps has shown that at equal light levels, a street that’s been lit at night by metal halide lights is brighter and safer than the same street lit by high-pressure sodium lamps. The new LED, or induction lights, emit a white light that provides high light levels and lower wattages, so they provide a brighter light at a lower cost.
East Sussex County Council became the first local authority to roll out a major LED street light conversion project, converting more than 11,000 sodium street lights in Eastbourne and Hastings to LED lights. The Council expects to save nearly £300,000 per year from reduced electricity and maintenance costs. Several other councils have followed suit, such as Gloucestershire, which is in the middle of a project to replace 55,000 street lights for an anticipated saving of £17 million over 12 years.
Over in Italy, Milan has become the first major city to have switched completely to LED lighting.
An American organisation called the Civil Twilight Collective – dedicated to reducing energy emissions – has developed a lunar-resonant street light, which is a variation on a conventional LED street light. These street lights increase or decrease their intensity depending on the light of the moon. So instead of wasting energy, it uses light in a very smart way by tapping into the moon’s cycle.
This street light design reduces energy consumption and cuts down on light pollution. Maybe it’s the way we should be going here in the UK.
