Lighting Lux Calculator: engineer's guide
The lumen method returns the number of luminaires needed to hit the target lux level given room area, luminaire output, and losses.
Open the Lighting Lux calculator →
What this calculator does
The calculator applies the standard lumen-method formula and reports luminaire count plus room grid spacing.
Formulas used
- Number of luminaires:
N = (E × A) / (F × CU × MF)
Variables
- E = required illuminance, lux
- A = area, m²
- F = luminaire flux output, lumens
- CU = coefficient of utilization, 0.4 to 0.7
- MF = maintenance factor, 0.7 to 0.9
Worked example
Scenario: 10 m × 8 m office, 500 lux target, 4000 lumen LED panels, CU 0.6, MF 0.8.
- N = (500 × 80) / (4000 × 0.6 × 0.8) = 40,000 / 1920 ≈ 20.8
- Round up to 24 luminaires in a 6 × 4 grid
- Verify uniformity ratio Emin/Eavg ≥ 0.6
Common mistakes to avoid
- Using initial lumens instead of maintained
- Same CU across different room shapes
- Ignoring wall reflectance in dark-finish spaces
- Missing task/ambient lighting split for offices
Frequently asked questions
Typical lux targets?
Office 500, corridor 100, warehouse 200, classroom 500, retail 500 to 1000, hospital surgery 1000+.
Uniformity requirement?
EN 12464-1: 0.6 for offices, 0.7 for classrooms, 0.4 for corridors.
Standards and references
EN 12464-1, IESNA Lighting Handbook, ASHRAE 90.1
Related tools on this site
Open the calculator that pairs with this guide: Lighting Lux Calculator.
Verification note
This guide is planning support only. Final design must be verified against the applicable project specification, authority requirements, manufacturer data, and the standards cited above. Consult a licensed engineer for construction-issue calculations.