What is evenness in indoor lighting?

Lighting uniformity is one of the standards described in the European standard NEN-EN 12464-1 that lighting installations must comply with. But what exactly is it and how do you calculate it? Whereas Lumen says something about the brightness of an individual fixture and lux value says something about the amount of light emitted on a given surface, uniformity is about how light is distributed in a room.

Evenness in the European standard NEN-EN 12464-1.

Within NEN-EN 12464-1, the number of lux the lighting must be for each type of room is described. For example, for a corridor this is 100 lux and for an office 500 lux. To meet the standard, you could install some very bright lights. This provides a lot of light, but also a lot of difference in light levels. Under the bright bulb there is a lot of light, however, between two fixtures there is a lot less light. In a hallway, this is not such a problem, which is a traffic space. In a workplace, this can already be a lot more annoying. There are then places with more than enough light, but also places where the light is insufficient.

That’s what evenness standards are for. The idea is not only to provide sufficient light for a task to be performed, but also to provide a calm and even light display. An example for workplace lighting in offices to indicate the differences in standards for lighting. The more precise the task, the higher the standard for light level and uniformity.

Calculating uniformity of lighting

The uniformity of lighting in a room is calculated by dividing the average illuminance by the minimum illuminance. The outcome must meet the standards described. Typically, light calculations are done in the program Dialux or Relux, for example. In this type of software, lighting in a room can be simulated and calculated. The program can also calculate how many fixtures are needed to achieve the standard.

For a light calculation, a room is entered into the chosen software. Length and width are important, as well as the height of the room and the mounting height of the fixtures. When the space is set correctly, the fixtures are drawn in. This is done by loading an Eulumdat (.ldt) file into the software. This file contains all the data of a luminaire’s beam.

Point lighting vs. line lighting

When choosing uniform lighting, light lines are often chosen in industrial halls. An important factor in this is that light lines provide high uniformity in the light display thanks to the favorable distribution of light. Below is an example of a 20-by-20-meter industrial hall equipped with Ocab Summus line lighting of 11,000 lumens per fixture.