What is the difference between lux and lumens?

Quelle différence entre lux et lumens ?

Lux vs. Lumens: Spotlight lighting

Lighting plays a crucial role in our daily lives, whether at home, in the office or in public spaces. Two terms often used in lighting are lux and lumens. Although these two concepts are related to brightness, they measure different aspects of light. In this article, we'll dive into the fundamental differences between lux and lumens, as well as their respective importance in lighting design.

1. Lux: The Measurement of Illuminance

Lux is a unit of measurement which evaluates the light illuminance on a given surface. Concretely, it measures the quantity of light that reaches a specific surface. In other words, lux takes into account both the light intensity and the area over which it is distributed. If you place a light source a specific distance from a surface, lux will measure the amount of light hitting that surface.

Lux formula

The lux formula is relatively simple:

= ˋ ˊ

This means that if you have a light source that emits 1000 lumens and you measure this light over an area of ​​1 square meter, the illuminance will be 1000 lux.

For example, suppose you have a light source that emits 1000 lumens and you want to measure the illuminance over an area of ​​2 square meters. The conversion would be as follows:

= 1000 2 2 = 500

So, in this example, the illuminance over the area of ​​2 square meters would be 500 lux.

It is important to note that converting lumens to lux also requires taking into account the uniform distribution of light across the surface, as the formula assumes a uniform distribution of light flux. If the light is not evenly distributed, additional considerations may be necessary to make an accurate conversion.

2. Lumens: Measuring Light Flux

Lumens, on the other hand, measure the total luminous flux emitted by a light source, without taking into account the surface area over which it is distributed. Luminous flux represents the total amount of light produced by a source, regardless of the direction in which it propagates.

Example of Lumens

Let's imagine an LED bulb that emits 800 lumens. This means that this bulb produces 800 lumens of light no matter where that light is pointed. However, this doesn't tell us anything about the actual brightness in a particular area.

3. When to use Lux and Lumens?

Lux: For an Accurate Assessment of Brightness

Lux is particularly useful when you need to measure brightness in specific spaces, such as offices, classrooms or work areas. By understanding the level of illumination on a surface, you can design lighting that meets the specific needs of that space.

Lumens: For the Choice of Light Sources

Lumens are often used when choosing bulbs or fixtures. It's a measurement that gives you an idea of ​​the overall brightness of a light source. The higher the lumens, the brighter the light source will be.


In summary, although lux and lumens are both related to brightness, they measure different aspects of light. Lux evaluates the illuminance on a given surface, while lumens measure the total luminous flux emitted by a light source. Understanding these two concepts is essential to designing effective lighting adapted to each situation. The next time you're choosing light bulbs or designing lighting for a space, remember to look at both lux and lumens to achieve an informed solution.

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