Illuminance Converter

THE PRACTICAL GUIDE · NORMANDIN SYSTEMS

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Illuminance Converter expresses the same illuminance measurement in another unit. It is useful when a specification, worksheet, instrument, or reference uses a different scale from the one you need. One foot-candle is approximately 10.7639 lux, based on lumens per square foot versus lumens per square metre. The numerical value changes because the unit changes; the underlying measured quantity stays the same. Illuminance is light arriving at a surface. Lumens describe luminous flux and cannot become lux without information about the illuminated area. Enter the measurement together with its source unit, then read the equivalent in the destination unit. Keep the full result while doing subsequent calculations and round only when preparing the final report. A converted value cannot be more precise than the original measurement, even when the calculator displays many decimal places.

Guide updated October 13, 2026

How to use this tool

1. Find the foot-candles input row. If a metric-prefixed row is hidden, clear Exclude SI prefixes to reveal the supported prefixed units.
2. Enter 1 into the foot-candles row for the worked example. Editing a row recalculates the other supported unit rows automatically.
3. Read the lux row; the example should give approximately 10.7639 lux. Keep the unit label with the number when using it elsewhere.
4. Replace the demonstration value with your measurement, preserving its source unit and meaningful precision. Review the relevant physical assumptions before applying the converted value.

SEE IT IN PRACTICE

A worked example

1 foot-candle

10.7639104167 lux

One foot-candle is approximately 10.7639 lux, based on lumens per square foot versus lumens per square metre.

Understand the area behind the unit

A foot-candle is based on lumens per square foot, while lux use lumens per square metre. The area relationship makes one foot-candle approximately 10.7639 lux. A smaller area unit produces a different numerical scale even though the illumination being described is unchanged. Preserve the full unit name because terms such as luminous intensity and luminance refer to other photometric quantities.

Measurement geometry still controls the comparison

A sensor at a desk, on a wall, or facing a light source can report different illuminance. Distance, angle, shading, and surrounding reflections also matter. Convert values to a common unit, then compare the measurement plane and conditions. A unit conversion does not predict how a fixture will illuminate a room or replace measurements at the locations relevant to the actual task.

Comparing meter readings

A light meter reading depends on the location and orientation of its sensor. Two readings in lux can differ because one was taken at a desk surface and another at the floor. Convert foot-candles and lux to a common scale, then compare measurement conditions. A numerical unit change cannot correct for a different measurement plane or shading of the sensor.

When this tool is useful

• Prepare consistent illuminance values for lighting measurement notes.
• Compare meter readings in lux and foot-candles without mentally switching between unit systems.
• Check surface-lighting unit checks before adding a value to a report or calculation.

Tips for a better result

• Illuminance is light arriving at a surface. Lumens describe luminous flux and cannot become lux without information about the illuminated area.
• Use lux as a common reference when comparing values from several sources; keeping one unit throughout a calculation makes dimensional errors easier to notice.
• Retain meaningful significant figures. Extra decimal places are useful for intermediate arithmetic, but do not imply that the original instrument measured with that precision.

Frequently asked questions