Lux – Planning Illuminance Correctly
How many Lux does my room need?
Lux (lx) is the unit of illuminance indicating how much luminous flux per square metre hits a surface. 1 Lux = 1 Lumen per m². For lighting design, the required Lux value is the starting point: it determines how many luminaires with what output must be installed. DIN EN 12464-1 defines minimum Lux values as maintained values – values that must not be undercut even after years of use. The formula for approximate calculation: Number of luminaires = (Lux × Area) / (Lumens per luminaire × Utilisation factor × Maintenance factor).
Calculation Example: Workshop 80 m²
Lux vs. Lumen vs. Watt: What Is the Difference?
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FAQ
How many Lux does an office need?+
500 Lux on the work surface for screen work, reading and writing (DIN EN 12464-1). In the immediate surrounding area at least 300 Lux. In corridors and traffic routes within the office 100 Lux.
How many Lux does a workshop need?+
Rough work: 300 Lux. Medium work (e.g. metalworking, assembly): 500 Lux. Fine work (electronics, watchmaking): 750 Lux. Very fine work (quality control): 1000 Lux. Additional task lights can achieve higher values locally.
How do I convert Lumens to Lux?+
Simplified: Lux = (Lumens × Utilisation factor × Maintenance factor) / Area. The utilisation factor (0.4-0.9) accounts for how much light actually reaches the work surface (depends on room geometry and reflectances). The maintenance factor (0.6-0.8) accounts for ageing and soiling. For exact calculation, DIALux or RELUX software is recommended.
Can you have too much Lux?+
Yes. Excessive illuminance wastes energy and can cause discomfort. DIN EN 12464-1 recommends not permanently exceeding 1.5 times the minimum value. More Lux also means more heat. Exception: Individual workstations with particularly high visual requirements can and should be specifically more strongly illuminated (task light).
How do I measure Lux values of an existing installation?+
With a lux meter (illuminance meter, from approx. €30). Measure on the work surface (typically 0.85 m height) at several points in the room. Measure both the average and uniformity (darkest / brightest point). Measure with daylight off (evening or darkened room). Compare values with the maintained value from the standard. If measured values are below the standard, retrofit or additional lighting is required.
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DIN EN 12464-1 – Workplace Lighting
DIN EN 12464-1 requirements: Lux values, UGR limits, colour rendering for office, industry, workshops. Overview table and practical tips for electricians.
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