Lumen Method Calculator (Number of Light Fixtures & Lux)

How to use the lumen method calculator

Enter the target illuminance, the room length and width, the lumens per fixture and the utilisation and maintenance factors. The calculator returns the exact number of fixtures, the number rounded up and the illuminance you will actually get.

Lumen method formula

N = E × A ÷ (Φ × UF × MF)  ·  E_achieved = N × Φ × UF × MF ÷ A

Worked example

An office 10 m × 8 m (80 m²) needs 500 lux, using 4,000 lm LED panels with UF = 0.6 and MF = 0.8:

• N = 500 × 80 ÷ (4,000 × 0.6 × 0.8) = 40,000 ÷ 1,920 = 20.83 → 21 fixtures
• Achieved = 21 × 1,920 ÷ 80 = 504 lux

Fixtures for an 80 m² room by application (4,000 lm, UF 0.6, MF 0.8)

Notes

• In practice round to a number that fits a neat grid (for example 21 → 4 × 5 = 20 or 4 × 6 = 24) and recheck the lux.
• The lumen method gives the average illuminance; use lighting software to check uniformity and glare.

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