Why some motorcycles have only one headlight on

Unlike older motorcycles that have a single dimmable headlight, modern motorcycles have two separate lights for dim and bright, and there is no reason to notify the rider about it. It’s completely normal.


We will have a look at why many motorcycles have only one headlight on and some other related topics around this; why manufacturers make motorcycles in this way, how lights affect a rider’s safety, how you can change your bike’s lighting system, and what type of headlights are the best for your motorcycle.

Why one of two?

As you may have noticed on sportbikes, motorcycles might have two headlights, and I often get people telling me to check my headlights because they see only one of them is working.

It is entirely normal for bikes to have this kind of setup. But the question is; why though?

When looking at functionality, motorcycles only need one dimmable headlight, but for the aesthetics, many have two headlights. Unlike a car, a motorcycle’s lights are very close to each other, and this makes it unnecessary to have both working at the same time.

When driving or riding at night, you would be able to estimate the distance of a car by your perspective of how far the headlights look apart. On a motorcycle, the lights are too close to each other to estimate distance adequately.

You might have learned back in school how we can measure distance through angles and a single measurement. This is called triangulation.

Your brain also does this when you look at an object with your two eyes; the closer an object is, the narrower your eyes will come to look directly at the object.

When an object is far away, we struggle to perceive the distance because the angle is too small. So when we look at a car’s headlights, the triangle is actually turned around; we perceive two lights from one perspective, which would be both our eyes or effectively one eye.

This makes it difficult to perceive the distance of a motorcycle because there is only a straight line between your eyes and the bike. We estimate the distance of a motorcycle by the brightness of the light and how the light moves and reflects on the road.

This is also very applicable to daylight riding/driving, even if you don’t realise your brain perceiving distance all the time in various ways.

Regarding human perspective, I would love to see a study on how a person’s workspace influences their perspective. Imagine if results showed that driving home after a long day behind a computer screen makes you more likely to cause an accident.

I think this information would be beneficial if the results do show this.

Why build bikes this way?

The only answer to why they build motorcycles with two headlights is because they can, and people like it. I like it, even though I do like the old school single headlight you still find on many new motorcycles today.

It just depends on what fits with the rest of the styling on the bike, and since it doesn’t matter if you have one or two lights, you can just as well save a bit and have separate lights for dim and bright instead of two dimmable lights.

In a way, having one light on instead of two kinda looks awesome.

Safer to have your headlights on

Today new motorcycles are all required to have the headlights turn on automatically when the bike starts; this was decided after many studies were done all over the world.

One such study revealed that a motorcyclist had a 27% lower risk of a crash if the headlights were turned on during the day. The study was a population-based case-control study in Auckland, New Zealand, between February 1993 and February 1996.

Source: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC387473/

Replacing your motorcycles headlights

Some might want to know if installing additional lights might help in safety.

While additional lights may be useful for safety, not all additional lighting is legal depending on where you live. On one of my previous motorcycles, I had LED lighting underneath the fuel tank that emitted light onto the engine.

Although this was legal where I lived, I had a switch on my handlebar to switch it on and off.

Final words

Many sportbikes and other motorcycles have two headlights; one for dim and one for bright. You can replace your bulbs and/or lighting system to make riding safer and also look good. You might also like another post: Why do some motorcycle’s brake lights flash?

I always try to keep my articles interesting and informative. And I’m always thankful when they are shared on social media platforms or Pinterest.

Two Motion

I don’t see myself as an expert in every topic of motorcycling but my articles usually relate to new experiences that are relevant at the time of writing.

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