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Lumen to Lux Calculator – Illuminance Converter

Convert lumens to lux based on area and calculate illuminance

Calculate Illuminance

Method and source check

Last checked:

Source and implementation check; this is not professional review or advice.

Method

The calculator converts square feet to square metres when necessary, divides luminous flux by illuminated area to obtain lux, and also reports the equivalent average illuminance in foot-candles.

lux = lumens / area in m²

foot-candles = lumens / area in ft²

1 ft² = 0.092903 m²

Variables and units

lm
luminous flux in lumens
lx
illuminance in lumens per square metre
fc
illuminance in lumens per square foot

Worked example

For 1,000 lm distributed over 10 m², illuminance is 1,000 / 10 = 100 lx, equivalent to about 9.29 foot-candles.

Limitations

  • This is an average-area calculation that assumes the entered luminous flux reaches the surface uniformly. It does not model distance, beam angle, fixture losses, reflections, obstructions, or compliance with a lighting standard.

Sources

Table of Contents

How to Use

  1. Enter the total lumens of your light source
  2. Enter the area to be illuminated
  3. Select your area unit (square meters or square feet)
  4. Click calculate to see the illuminance in lux

What is Lux?

Lux (lx) is the SI unit of illuminance, measuring the amount of light that falls on a surface. One lux equals one lumen per square meter (lm/m²). It describes how bright a surface appears based on the light it receives.

Unlike lumens, which measure total light output, lux measures light intensity at a specific location. The same light source will produce different lux values depending on the distance and area it illuminates.

Lumens vs Lux

Understanding the difference between lumens and lux:

  • Lumens (lm): Total amount of visible light emitted by a source
  • Lux (lx): Amount of light falling on a surface per unit area
  • Formula: Lux = Lumens / Area (in square meters)
  • 1 lux = 1 lumen per square meter
  • 1 foot-candle = 1 lumen per square foot ≈ 10.764 lux

Lighting Design Applications

Lux calculations are essential for:

  • Architectural lighting design
  • Workplace safety and compliance
  • Photography and videography setup
  • Retail and display lighting
  • Sports facility illumination
  • Road and street lighting design
  • Museum and gallery lighting
  • Energy-efficient lighting planning

Frequently Asked Questions

What is the difference between lumens and lux?
Lumens measure the total light output from a source, while lux measures how much light falls on a surface. The same number of lumens spread over a larger area results in lower lux values.
How many lux do I need for reading?
For comfortable reading, 300-500 lux is recommended. For detailed reading or for older adults, 500-750 lux or higher may be more comfortable.
How do I increase lux without changing bulbs?
You can increase lux by: moving lights closer to the surface, using reflective surfaces to bounce light, adding more light fixtures, or reducing the area you're trying to illuminate.
What is a foot-candle and how does it relate to lux?
A foot-candle (fc) is the imperial unit of illuminance, equal to one lumen per square foot. One foot-candle equals approximately 10.764 lux. It's commonly used in North America for lighting specifications.

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