When you want to know how much light a particular light source emits, you often look at the number of lumens stated on the lamp. However, this does not immediately tell you how much light from the lamp reaches, for example, your desk or workplace. We do not measure this in lumens, but in lux.

What is lux?

Put simply, lux is the amount of light that falls on a surface. More specifically, lux is the number of lumens (the light emitted by the lamp) per square metre, and is therefore also expressed as lm/m­­². The number of lux is affected by the distance between the light source and the surface being measured. Logically, more light falls on a surface that is 1 metre from the light source than on a surface that is 5 metres away. Think of a reading lamp that you switch on in the evening: under the lamp, you can read your book easily because the lux levels are high there. But if you sit a little farther away from the lamp, you can barely read the book anymore. The number of lumens emitted by the lamp remains the same, but the number of lux on the pages of your book has decreased.

What are typical lux levels?

There are, of course, also guidelines for assessing whether the lux levels in a room are sufficient. In offices, for example, lux levels of approximately 300–500 lx are used. By comparison, indirect sunlight has a value of approximately 10,000 lux, while a living room often has only 50 lux. The required lux level naturally depends mainly on the function of the room.

When are lux levels important?

Lux levels are therefore important when you want to assess whether a surface or workplace is sufficiently illuminated, or when creating a lighting plan. Naturally, the light output of the light source is related to this, but it is also important to consider the placement of the light source. This has a significant impact on the number of lux on a surface. When we at Qub create a lighting plan, we therefore look not only at the number of lumens emitted by the lamp, but also primarily at the lux levels on different surfaces.