Seeing Red: The Science Behind Why Tail Lights Are Red

Red is danger. Red is caution. Red is stop. Also, red lights are common in motorcycle and car tail lights. Universal as well.

So why are vehicle tail lights red? Red color light has the longest wavelength which makes them visible from long distances easily. Coupled with the red symbol for caution and stop, a red tail light acts as a better safety light on a vehicle.

Seeing the red tail light, the other vehicles behind will slow down.

That’s why, all vehicles – be it cars, motorcycles, or trucks – have red color tail lights or backlights.

In addition, most road laws and regulations across the world mandate the tail lights to be red in color.

That’s the gist. Now let’s dive deeper.

Red in the visible light spectrum

Before we dive into why red is used in vehicle tail and backlights, it’s important to understand the visible spectrum and red’s place in it.

The visible light spectrum, put simply, is the wavelength range that a human can see. This is the only segment of the electromagnetic spectrum that is visible to humans. Hence the name, visible light spectrum.

Now, within the visible light spectrum, we have 7 colors of differing wavelengths.

These seven colors, as you might have guessed by now, are the rainbow colors – often shorthand called as VIBGYOR.

Each of these colors has different wavelengths, here is the data:

The wavelengths of visible light are:

Color	Wavelength
Violet & Indigo	380–450 nm
Blue	450–495 nm
Green	495–570 nm
Yellow	570–590 nm
Orange	590–620 nm
Red	620–750 nm

Of these colors, red has the longest wavelength. And hence, has the shortest frequency.

This longer wavelength of red has its uses. It makes the red color visible from long distances as compared to others.

That’s the reason why red color light is used on top of the towers.

And that also brings us to why vehicle tail lights are red too.

Reasons why vehicle tail lights are red

Here are the main reasons why vehicle tail lights are red:

1. Easier to see from a distance: Red light has the longest wavelength among the visible spectrum colors (with violet having the shortest wavelength). The long wavelength of red makes it easier to see it from a distance by other vehicles on the road.
2. Higher visibility in fogs and rains: Red color is easier to spot in low visibility conditions like rain, fog, dust, and winter roads. In addition, red lights have great visibility at night time too.
3. Symbol of caution and stop: Red color is universally seen as a symbol of danger, caution, and a stop signal. When a vehicle behind, sees the red tail light shining on the vehicle in front, the driver will show caution and slows down accordingly.
4. Better safety: Combined with better visibility and the symbol for caution, the red light acts as the perfect safety tail light option in a vehicle over any other color light.
5. Road laws and regulations: Legislatures across the world mandate the tail lights to be red in color. Any other color tail lights are prohibited.

In short, the higher wavelength of red color light makes them visible from long distances. Coupled with the red symbol for caution and stop, a red tail light acts as a better safety light on a vehicle.

Seeing the red tail light lightened, the other vehicles behind will slow down.

Cars, motorcycles, and all other vehicles

The red tail light is universal across all automobiles. Be it cars, motorcycles, trucks – all the vehicles have the red tail and back lights.

So whenever the vehicle brakes, the tail light lights up. The red tail light brightened up – cautions the vehicle behind to slow down.

Even symbolically, the red tail light when brightened because of the vehicle braking – kind of gives a stop signal to the vehicles behind it.

As a result, red tail lights act as better safety color tail lights in these vehicles. If there was any other color used, the effectiveness would definitely have been lost.

Yellow or Orange indicator lights

You might have noticed just how the tail lights are red in color, the turn key indicator lights are yellow or orange in color. Universally.

This is no coincidence either.

If you go back to the visible light spectrum and the wavelengths again, yellow and orange have the next longest wavelengths to red.

This again helps in visibility over a long distance. And keeping the indicator lights yellow or orange makes it distinguishable from the tail lights.

So to keep the indicator lights distinguishable from the tail light, and yet make them visible at a distance – yellow or orange color lights are used in turn key indicators.

Is it mandatory to have red tail lights?

In a way, yes. Vehicle tail lights need to be red in color.

Road laws and legislations across the world mention, some direct and some implicit, that the tail lights must be in red color.

The tail lights are not to be tampered or modified.

So, even if you are replacing the tail light, backlight, or brake light (whatever you prefer to call them), you must replace it with a red color light only.

Any kind of color customization on the vehicle lights is prohibited in almost all regions worldwide.

So, don’t change the backlight color. Keep it simple and red.

Before you go…

Now that we know about tail lights and their color, here are a few more posts related to motorcycle lights:

• Motorcycle headlights – Halogen vs HID vs LID
• Reasons some motorcycles only have one headlight on
• Dim headlight – causes and solutions