Illuminance Converter
Converters · Added 15 August 2026
Convert illuminance between lux, foot-candles and the older CGS units. Illuminance measures light arriving on a surface — one lux is one lumen per square metre — which makes it distinct from a lamp's lumen output and from the candela rating of a beam.
Result
1 fc in lux (lumen per m²)
10.7639104 lx
1 fc = 10.7639104 lx
The same value in every unit
- Lux (lumen per m²) (lx)
- 10.7639104
- Kilolux (klx)
- 0.0107639104
- Millilux (mlx)
- 10,763.9104
- Foot-candle (lumen per ft²) (fc)
- 1
- Phot (lumen per cm²) (ph)
- 0.00107639104
- Milliphot (mph)
- 1.07639104
- Nox (nox)
- 10,763.9104
Lux measures light falling on a surface, so it depends on distance from the source. A lamp's lumen rating is fixed; the lux it delivers to your desk falls with the square of how far away you move it.
How to use the illuminance converter
- 1Enter the illuminance value from your light meter or specification.
- 2Pick its unit — lux in most of the world, foot-candles in US lighting practice.
- 3Choose the unit you want.
- 4The table shows the same illuminance in every unit at once.
- 5Swap the units to reverse the conversion.
Examples
US lighting spec to metric
- Input
- 50 fc
- Result
- 538.20 lx
American lighting standards are written in foot-candles; European ones in lux.
An office lighting level
- Input
- 500 lx
- Result
- 46.45 fc
A common design target for general office work.
Photographic units
- Input
- 1 phot
- Result
- 10,000 lx
The phot is one lumen per square centimetre — a very bright level, hence the large lux figure.
About the illuminance converter
Four quantities that describe light
Lighting has four related but distinct photometric quantities, and confusing them is the source of most lighting-specification errors. Luminous flux, in lumens, is the total light a source emits. Luminous intensity, in candelas, is the light emitted in a particular direction — which is why a focused torch and a bare bulb can share a lumen rating and differ enormously in candelas.
Illuminance, in lux, is what this converter handles: light arriving on a surface, per unit area. Luminance, in candelas per square metre, is light leaving a surface toward an observer, which is what corresponds to perceived brightness.
All four are weighted by the human eye's spectral response rather than measuring raw radiant power. That is why a photometric measurement is not a physics measurement of energy: 1 watt of green light at 555 nm produces about 683 lumens, while 1 watt of deep red or violet produces far fewer, because the eye is much less sensitive there.
Reading a lighting level in context
Illuminance levels in daily life span an extraordinary range. Full direct sunlight is on the order of 100,000 lux; an overcast day perhaps 1,000; a well-lit office around 500; a living room in the evening perhaps 50; and full moonlight well under 1 lux. The eye handles this range through adaptation, which is why a room that feels perfectly bright can measure a small fraction of what daylight delivers.
That adaptation is exactly why measured lux and perceived adequacy diverge. Lighting standards specify task illuminance because the eye's impression is unreliable — a space can feel well lit while delivering far too little light for detailed work, particularly for older readers, whose retinas receive considerably less light than a young person's at the same measured level.
Uniformity matters alongside the absolute number. A room averaging 500 lux with bright pools and dark corners is a worse working environment than one evenly at 400, because the eye must readapt as it moves between them. Good lighting design is as much about controlling the ratio between brightest and dimmest as about hitting a target figure at one point on a desk.