About this calculator
Estimates the number of luminaires needed to reach a target illuminance (lux) level in a room, using the lumen method: total lumens needed, then divided by luminaire output.
Formula
lumens needed = room area (m²) × target lux / (utilisation factor × maintenance factor)
luminaires = ceil(lumens needed / lumens per luminaire)
The utilisation factor accounts for light lost to walls, ceiling, and furnishings before it reaches the working plane; the maintenance factor accounts for expected lamp/luminaire output loss over time from dirt and ageing.
Worked example
Defaults: 5 m × 4 m room, 300 lux target, 0.6 utilisation factor, 0.8 maintenance factor, 3000 lm luminaires.
area = 20 m²
lumens needed = 20 × 300 / (0.6 × 0.8) = 6000 / 0.48 = 12,500 lm
luminaires = ceil(12,500 / 3000) = 5
FAQ
Why doesn't the calculator offer lux presets for different room types? EN 12464-1 sets recommended lux levels for many specific room and task types, but this calculator does not look those specific figures up with confidence — enter your own project's required lux level from its own lighting design standard or specification.
What are typical utilisation and maintenance factor values? Both depend heavily on room geometry, surface reflectance, and the luminaire/lamp type — the defaults here (0.6 and 0.8) are generic indoor-lighting estimates, not derived for your specific room.
Why doesn't the calculator cite a standard?
No specific illuminance level, utilisation factor, or maintenance factor is cited with
confidence here, so meta.standards is left empty — the lumen method formula itself is
standard photometric practice, not something needing its own citation.
Assumptions and limits
Target lux, utilisation factor, maintenance factor, and luminaire output are all disclosed estimates you should adjust to match your own project's lighting design and product data.