Illuminance Converter

Convert illuminance values among common SI, metric and customary units. Illuminance is luminous flux arriving per unit area. One lux is one lumen per square meter.

ValueEnter zero or a positive value; scientific notation is accepted.Convert fromLux (lx)Kilolux (klx)Foot-candle (fc)Phot (ph)Convert toLux (lx)Kilolux (klx)Foot-candle (fc)Phot (ph)

Convert

Converted value46.45152 fc

SI-base value500 lx

Multiply by0.09290304

The displayed results apply to the default example. Enable JavaScript to convert other values.

How to use this converter

1. Enter the illuminance value.
2. Select its current unit and the unit you want.
3. Select Convert. The page shows the converted value, the SI-base value and the direct multiplication factor.

Conversion formula

Converted value = entered value × source-to-SI factor ÷ target-to-SI factor.

Every option is represented by its factor to lux (lx). This one-base method keeps reciprocal conversions consistent. Calculations run in your browser, and old results are hidden when an input changes or validation fails.

Worked example

Convert 500 lx to fc. Multiply by 0.09290304; the result is 46.45152 fc. The same input equals 500 lx in the SI-base unit.

Accuracy and limitations

Illuminance at a point does not fully describe glare, uniformity, color rendering or visual comfort. Use appropriate lighting standards for design.

The calculator retains more digits internally than it displays. Round the final value to the precision supported by your measurement. Very large and very small answers may use scientific notation.

Frequently asked questions

What is the relationship between lux and foot-candles?

One foot-candle equals about 10.7639 lux.

Can I reverse the conversion?

Yes. Swap the From and To selections. Because both units use the same SI base, the reverse factor is the reciprocal of the forward factor.

Why was my entry rejected?

Use digits with an optional decimal point or scientific notation. Blank values, commas, fractions, words and non-finite entries are rejected. Negative values are rejected because this converter treats the quantity as a magnitude.

Review notes and sources

Reviewed October 4, 2026. The conversion factors, default example, zero or signed boundary behavior, invalid-input handling and recovery after an error were checked. Factors follow SI definitions and published conversion guidance from the NIST Guide to the SI and the BIPM SI Brochure. Explanations and examples are original.

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