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Illuminance (Lux) Calculator

Work out illuminance (lux) instantly with clear inputs, formula shown and shareable results.

About Illuminance (Lux) Calculator

Illuminance is luminous flux per square metre, and one lux is one lumen per square metre. 2000 lumens spread over 8 m2 gives 250 lux, adequate for a living room but short of the 500 lux an office desk needs. Illuminance falls as the lit area grows, which is why ceiling height matters as much as lamp output.

Formulas

Illuminance

E = luminous flux / area

Unit relation

1 lx = 1 lm/m2 = 0.0929 foot-candles

Worked example

With the default values below, Illuminance (Lux) Calculator returns Illuminance of 250.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Luminous flux reaching the surfaceminimum 0 lm
2,000 lm
Area illuminatedminimum 0 m2
8 m2

Results

Illuminance
250.00 lx
Same Illuminance In Foot-Candles
23.226
Lighting Assessment
Adequate for general living areas
Lumens Per Square Metre
250.00

Step by step

  1. 1Values used
  2. 2Illuminance
  3. 3Unit relation
  4. 4Illuminance= 250.00 lx
  5. 5Same Illuminance In Foot-Candles= 23.226
  6. 6Lighting Assessment= Adequate for general living areas
  7. 7Lumens Per Square Metre= 250.00

Assumptions and limits

  • The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How much light does a room need?

Roughly 100-200 lux for circulation, 300 lux for living areas, 500 lux for office work and 750-1000 lux for detailed tasks.

Why do lamps advertise lumens rather than lux?

Because lux depends on how far away and over what area the light falls. Lumens describe the lamp; lux describes the situation.

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Illuminance (Lux) Calculator – Calculate Illuminance