Free Electrical calculator

Lux and lumen preliminary calculator

Use the lumen method to estimate average illuminance or preliminary lamp lumens required.

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All values remain in your browser. Review the assumptions before using the result.

Your result will appear here.Calculate to see the outputs, formula and substituted working.

How the calculation works

Preliminary lumen-method average illuminance relationship.

Formula

E = N × Φ × UF × MF ÷ A

Worked example

Luminaires10 × 5,000 lm

Area100 m²

UF / MF0.60 / 0.80

Expected average illuminance240 lx

Assumptions and limitations

Assumptions

UF and MF are selected by the user.
Lamp/luminaire lumens are appropriate to the intended calculation.

What this does not check

Does not model photometric distribution, spacing, uniformity, glare or reflectance.
Does not verify emergency lighting, daylight or task-specific criteria.

Formula version: 1.0 · Last reviewed: 16 August 2026

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Engineering basis: first-principles electrical relationships using user-entered values. The page does not reproduce BS 7671 tables or establish compliance. Complete the project-specific design against the current BS 7671 information, manufacturer data and the applicable project requirements.

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