Lighting Lumen Calculator
Use the lumen method to work out how many luminaires are needed to reach a target illuminance (lux) in a room, plant area or control room.
- N = E × A ÷ (Φ × UF × MF) = 500 × 96 ÷ (4,000 × 0.6 × 0.8) = 25
Typical recommended illuminance
| Area | Illuminance |
|---|---|
| Corridors and stairs | 100 lux |
| Plant rooms and switch rooms | 200 lux |
| General offices | 500 lux |
| Control rooms | 300 to 500 lux |
| Fine assembly and inspection | 750 to 1000 lux |
The Lumen Method
E is the target illuminance (lux), A the floor area (m²), Φ the lumen output of one fitting, UF the utilisation factor (light reaching the work plane, from the luminaire data) and MF the maintenance factor for dirt and lamp ageing.
Worked example
A 12 × 8 m office at 500 lux with 4,000 lm fittings, UF 0.6, MF 0.8: N = 500 × 96 ÷ (4,000 × 0.6 × 0.8) = 25 fittings.
Frequently Asked Questions
What is the lumen method?
A simple way to find the number of luminaires for a target average illuminance using lumen output and correction factors.
What utilisation factor should I use?
It comes from the luminaire photometric data and depends on room size and reflectances. 0.5 to 0.7 is common for offices.
What maintenance factor is typical?
About 0.8 for clean areas with LED fittings, down to 0.6 for dirty industrial environments.
Learn more on the blog
Electrical units of measure explained
A practical, field focused guide on instrumentationblog.in that explains the theory behind this calculator and how engineers apply it on real plants.
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