If you’re someone who spends a lot of time driving at night, you’ll be really familiar with that orange glow of street lights.
But have you ever wondered why the orange color was chosen?
Would it not have made sense to use a cooler light temperature that would be better for concentration while driving?
Simply, street lights are yellow or orange because the majority of them are either low-pressure sodium (LPS) or high-pressure sodium (HPS), which at the time of installing street lights was much more efficient than incandescent bulbs. LPS and HPS can only emit orange light.
In this article we’ll dive a little deeper into:
- Why street lights are orange
- Why sodium was used in street lighting
- Why LEDs aren’t used
Why Are Street Lights Orange?
Street lights give off an orange light is not an active choice by manufacturers but a result of the bulbs used.
Most street lights used in modern society are made using sodium vapor. There are two types – low-pressure sodium (LPS) and high-pressure sodium (HPS).
HPS lights are slightly more efficient and somewhat cooler in temperature than LPS. However, they are still firmly in the warm orange range.
LPS lights tend to be used more under bridges or tunnels and were generally adopted more in Europe.
Most street lights are, however, HPS.
LPS lights contain argon and neon gas, which light up when a current is passed through them.
These gasses increase in temperature, which then vaporizes the sodium, creating the yellow-orange light that you see.
HPS lights instead use a pressurized tube that contains sodium, mercury, and xenon.
They work the same way, but the difference is that the xenon and mercury will give more of a blue-white first before the sodium vaporizes and combine with the yellow-orange sodium light to create an overall more ‘white’ color.
It’s worth noting that color-corrected sodium vapor lighting does exist. Still, the bulbs are much more expensive and have a lower lifespan.
Some arguments suggest orange lighting has a better fog penetration than white light, but also that whiter lights give drivers better peripheral vision and therefore improved braking speeds.
There’s no formal study into these and that’s why fog lights on cars can be yellow, amber or white.
Why Is Sodium Used In Street Lighting?
So why did authorities decide to use sodium vapor lighting? The only reason is a straightforward one – cost.
Sodium vapor lights are more efficient than the other bulb options that were available at the time.
That’s because they only produce light that is at a visible frequency to the human eye.
Other bulbs such as incandescent create light across all frequencies, from infrared to UV.
This full-spectrum lighting is essentially wasting power.
The lumens per watt of an HPS bulb is around 7 times more efficient than an incandescent bulb on average, and with a much longer lifespan too.
So if a sodium light is just as bright but uses less power and lasts longer, why would the authorities have chosen any other option for the millions of street lights used worldwide?
It wouldn’t make sense.
|Bulb Type||Lifespan||Lumens per watt|
It’s worth noting that these are average values and will vary by the bulb.
Sodium vapor lights were invented back in the 1930s, with HPS lights being created later in 1970.
They became really popular in the 1980s in street light use, at least with those responsible for the lights – some people may not have liked the orange glow, although many became accustomed to it.
Why Are Street Lights Not LED?
So, if the main reason incandescent bulbs weren’t used in street lighting was efficiency, why wasn’t LED considered an alternative?
Especially when you look at how they closely match the efficacy and have a much longer lifespan.
Well, the first visible LED lights were only created in 1962, and by this point, a lot of street lights were either already in place or planned.
The new technology takes time to be adapted for broader use.
Not only that, but LEDs were costly at the time – around $200 per bulb! That’s a considerable amount, and imagine paying that on a per-bulb basis for street lights.
New York City alone has 250,000 street lights, so you’re talking $50 million for the bulbs alone, never mind the costs of the other materials and installation.
Obviously, as with any technology, LEDs have come down in price over the years and are now comparable prices with other bulb technologies.
Some street lights have started using LEDs already, and we’ll no doubt see more cities worldwide adopting LED tech in the future.
It’s all about the cost, though, so don’t expect any authorities to replace street lights with LEDs while the sodium ones are working sufficiently.
It will only be as they start to burn out or need replacing that the changes will be made.
Also read: Can LED Lights Power Solar Lights?
As with so many decisions made by those in charge of public facilities, the reason that street lights give off that orange glow is just that they were the most cost-effective choice when the lights were first installed.
That’s not a bad thing, though, because they have worked as required for many years. While the color isn’t ideal – it can make it difficult to correctly identify certain shades, which could impact reporting accidents with other cars that drive off.
For example, they have otherwise provided sufficient light to keep people safe without meaning huge charges in public taxes.
But, we can look forward to a future where LEDs will likely become much more prominent, as they are in so many other uses.
Some people are actually nostalgic for the orange glow, though – how do you feel about the modernization of street lights?
Will you miss the orange hue, or do you not care either way?