💡 Illuminance

Illuminance Converter

Light levels for offices, studios, warehouses and photography — convert lux, foot-candles and phot. Enter a value and press Convert.

Written and reviewed by SM Arijul Islam · Last reviewed 28 October 2026 · Editorial standards · Report an error

About the illuminance converter

Illuminance describes how much light falls on a surface, measured in lux — one lumen per square metre. It is different from luminance, which measures the light leaving a surface, and from luminous flux, which is the total output of a lamp in lumens.

Factors used

1 lux = 1 lumen per square metre
1 foot-candle = 10.7639104 lux
1 phot = 10,000 lux
1 nox = 0.001 lux
1 kilolux = 1,000 lux

Typical light levels

Overcast day outdoors: 1,000 – 5,000 lux
Direct sunlight: 32,000 – 100,000 lux
Office or classroom: 300 – 500 lux
Living room: 100 – 200 lux
Full moon at night: about 0.3 lux

Recommended office lighting of 500 lux is roughly 46 foot-candles.

How to convert illuminance

Illuminance measures how much light arrives at a surface, in lux (lx), where one lux is one lumen spread over one square metre. The foot-candle is the imperial equivalent — one lumen per square foot — so 1 fc is about 10.7639 lx. Because illuminance falls with the square of distance from a source, the same lamp produces very different lux readings at 1 m and at 3 m.

Common illuminance conversions

One lux expressed in other units of illuminance
Unit	1 lux equals
Lumen per square meter (lm/m²)	1
Foot-candle (fc)	0.09290304
Lumen per square foot (lm/ft²)	0.09290304
Kilolux (klx)	0.001
Phot (ph)	0.0001

Everyday uses

Planning lighting for rooms and offices
Photography, film and exposure settings
Workplace and safety lighting standards
Grow lights for plants
Screen and display brightness checks

Frequently asked questions

How many lux is a foot-candle?

About 10.7639 lx, because one square foot is 0.092903 square metres.

How much light is daylight?

Overcast daylight is roughly 1,000–5,000 lx, direct sunlight can exceed 100,000 lx, and a typical living room sits around 100–300 lx.

What is the difference between lux and lumens?

Lumens measure the total light a source emits; lux measures the light arriving at a surface, so distance and beam spread both matter.

How bright should an office be?

Many guidelines suggest around 300–500 lx on the working plane for general office tasks.

How many foot-candles is 500 lux?

500 lux × 0.09290304 = 46.45 foot-candles. To reverse it, multiply foot-candles by 10.7639 to get lux.

More worked examples

A well-lit office sits at around 500 lux.
A moonlit night outdoors is roughly 0.1 to 0.3 lux.
Direct sunlight reaches about 100,000 lux.
One foot-candle is about 10.7639 lux.

Typical illuminance levels

Approximate illuminance levels for common environments
Environment	Approximate illuminance
Full moon, clear night	about 0.1 to 0.3 lux
Living room	about 150 lux
Office or classroom	about 300 to 500 lux
Overcast day	about 1,000 lux
Full daylight, indirect	about 10,000 to 25,000 lux
Direct sunlight	about 100,000 lux

Common mistakes to avoid

Confusing lux with lumens. Lumens measure how much light a lamp emits, while lux measures how much light lands on a square metre of surface.
Assuming a brighter bulb always means a brighter room. Distance matters enormously, because illuminance falls with the square of the distance from a point source.
Mixing foot-candles and lux. One foot-candle is 10.7639 lux, not 10 exactly.
Treating recommended levels as universal. They vary by task, by standard and by country.

Further questions

How do I convert foot-candles to lux?

Multiply by 10.7639, the number of square feet in a square metre.

What is a comfortable light level for reading?

Around 300 to 500 lux is usually comfortable for extended reading without straining.

Does illuminance drop with distance?

Yes. From a point source, illuminance falls roughly with the square of the distance, so twice as far away gives about a quarter of the light.

Sources and standards

Illuminance is luminous flux per unit area, measured in lux, and it is a photometric quantity weighted to human vision. The SI Brochure defines the candela through a fixed luminous efficacy, and NIST SP 811 lists the photometric units used here.