What do lumens and lux mean for auxiliary driving lights?

Lumens and lux are two different measurements used to describe light.

They are important to understand when comparing auxiliary driving lights and LED light bars, because high light output does not automatically mean a light has a long range.

What are lumens?

Lumens (lm) describe the total luminous flux from a light source.

A higher lumen value generally means the light emits more light overall.

However, it does not tell you how the light is distributed or how far it reaches.

What is lux?

Lux (lx) describes how much light falls on a given surface.

One lux equals one lumen per square metre.

In vehicle lighting, lux is often used to describe a light’s range.

For example, manufacturers may state the distance at which the light provides an illuminance of 1 lux.

What does 1 lux at 500 metres mean?

It means that, according to the manufacturer’s measurement, the light provides an illuminance of 1 lux at a distance of 500 metres.

This is a common way to compare the range of auxiliary driving lights.

Remember that 1 lux does not mean the entire road is well lit at that distance. It normally describes a specific point in the beam pattern.

Are more lumens always better?

No.

Two lights can have the same lumen value but completely different beam patterns.

One light may spread its light widely and provide good visibility to the sides, while another concentrates it forwards and achieves a longer range.

It is therefore important to compare lumens, lux and beam pattern.

Tip: Check whether the manufacturer gives theoretical or measured lumen values. Measured values normally give a better indication of the light’s actual luminous flux.