Measuring illuminance - how to check lux at the workplace?
Illuminance in lux decides whether a task can be carried out safely and without eye strain. This guide shows how to measure correctly with a lux meter to EN 12464-1, which nominal values apply per task, and how to set up the measurement grid and maintained value.
View lux metersWhat does a lux meter measure and why in lux?
A lux meter measures illuminance, the luminous flux per area in lux (lx = lumens per square metre). The sensor weights the light according to the sensitivity of the human eye (V-lambda matching) and corrects obliquely incident light through the so-called cosine correction.
EN 12464‑1 defines the required nominal illuminance values for indoor workplaces depending on the visual task. They are defined as maintained values: the average must not fall below this value over the service life despite ageing of the luminaires.
- Lux (lx): illuminance on the working plane, this is the reading.
- Lumen (lm): the total luminous flux of a light source.
- Candela (cd): the luminous intensity in one direction.
- Maintained value: required minimum average to EN 12464‑1.
Which nominal values apply per task?
The finer the visual task, the higher the required maintained value. Coarse work needs 200 to 300 lx, while fine assembly or inspection needs 750 to 1000 lx. The following reference values to EN 12464‑1 help you assess your measurement.
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Read the guideHow do you measure correctly using a grid?
Measurement takes place on the evaluation surface at the height of the visual task, usually 0.85 m above the floor for seated work or on the actual working plane. The area is divided into a grid, a reading is taken at each grid point and the average is formed.
- Place the sensor horizontally at the measuring height and avoid casting your own shadow.
- Distribute grid points evenly (derive the grid spacing from room geometry per EN 12464‑1).
- Let the lighting warm up for 20 to 30 minutes before measuring, especially fluorescent and LED luminaires.
- Document or shade external light such as daylight when only artificial light is assessed.
- Calculate the average and the uniformity (Uo = minimum divided by average).
Take the maintained value into account: freshly installed luminaires initially deliver more lux than required because a maintenance factor covers ageing over the service life. An acceptance measurement should therefore lie clearly above the nominal value.
Frequently asked questions
At what height is illuminance measured?
Usually on the evaluation surface at the height of the visual task. For seated work this is typically 0.85 m above the floor, otherwise the real working plane.
How many measuring points are needed?
The grid spacing follows from the room geometry per EN 12464‑1. Larger areas need more points; the individual readings give the average and the uniformity.
Why is the reading above the nominal value right after installation?
The nominal value is a maintained value. New luminaires deliver more light because a maintenance factor accounts for ageing and soiling over the service life.
Is a simple smartphone lux meter enough?
For rough orientation yes, for standard-compliant assessment no. You need a device with V-lambda matching, cosine correction and calibration to DIN 5032‑7.
Looking for the right lux meter?
We supply calibrated lux meters with V-lambda matching and cosine correction - suitable for measurements to EN 12464-1.
Standard-compliant
Instruments for measurements to EN 12464-1.
Calibrated
V-lambda matching and cosine correction included.
Precise
Accuracy class to DIN 5032-7.
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