💡 Illuminance Converter (Lux, Foot-candle, Phot, Nox)
By Shihab Mia · Updated 2026-07-30
Type in any box and every other unit updates instantly.
This illuminance converter changes a light level between lux, foot-candles, phot, nox and kilolux. Illuminance is how much light lands on a surface, and different fields quote it in different units: most of the world uses lux, while North American lighting plans still lean on foot-candles. Type a value into any box and every other unit updates instantly using exact conversion factors, so you can read a spec, a light-meter reading, or a lighting standard in whatever unit you need.
What is the Illuminance Converter?
Illuminance measures the luminous flux (in lumens) that falls on a unit of area. One lux is one lumen spread over one square metre, so lux is simply lumens per square metre. The foot-candle is the imperial counterpart: one foot-candle is one lumen falling on one square foot. Because a square metre is larger than a square foot, the same lumens spread over a square metre give a smaller number, which is why one foot-candle equals 10.7639 lux (the number of square feet in a square metre).
The phot is an older CGS unit equal to one lumen per square centimetre. Since a square metre holds 10,000 square centimetres, one phot equals 10,000 lux. The phot is rarely used in modern practice but still appears in older instruments and textbooks. At the opposite extreme, the nox is one thousandth of a lux (1 nox = 0.001 lux) and is used to specify extremely low light levels, such as the sensitivity of night-vision gear or security cameras rated for near total darkness. Kilolux (1,000 lux) is handy for bright outdoor levels: full daylight is roughly 10 to 25 kilolux, and direct sunlight can exceed 100 kilolux.
Illuminance is not the same as luminance or luminous intensity. Illuminance (lux, foot-candles) describes light arriving at a surface and is what a light meter reads. Luminance describes brightness leaving a surface toward your eye, and luminous intensity (candela) describes light from a source in a given direction. When a lighting standard specifies a target, it almost always means illuminance on the working plane, so lux and foot-candles are the units you convert between most often.
A lux meter (also called a photometer or illuminance meter) reads illuminance directly at a single point, and that reading only applies to the exact spot and angle where it was taken. For a point source like a bulb, illuminance follows the inverse-square law: doubling the distance from the source cuts the reading to a quarter, and tilting the sensor away from the light reduces it further by the cosine of the angle. That is why two readings taken a metre apart in the same room, or at different times of day outdoors, can differ substantially even though nothing about the light source has changed.
Lux is easy to confuse with lumens and watts, but all three measure different things. Lumens measure the total light a source emits in every direction, lux measures how much of that light actually lands on a surface, and watts measure raw electrical or radiant power, not perceived brightness. Because lux is weighted by how sensitive the human eye is to different colours, there is no single factor that converts watts or lumens straight to lux, you always need to know either the illuminated area or the light source's specific output.
When to use it
- Reading a North American lighting plan in foot-candles when your light meter reports lux.
- Converting an office or workplace lux requirement into foot-candles to match a US specification.
- Checking that a photography or videography light reading meets a target in either unit.
- Translating an older instrument reading given in phot into modern lux.
- Comparing a security camera or night-vision device minimum lux rating against a real light-level reading.
- Comparing plant grow-light or greenhouse lighting specs that mix lux and foot-candle units.
How to use the Illuminance Converter
- Type your known light level into the box for its unit, for example lux or foot-candles.
- Read the equivalent value from every other unit box, which updates as you type.
- Use kilolux for bright outdoor levels and phot or nox only for legacy or specialist readings.
- Press Clear to reset all boxes and start a new conversion.
Formula & method
Worked examples
Convert an office target of 500 lux into foot-candles.
- Use foot-candles = lux / 10.7639
- foot-candles = 500 / 10.7639
- foot-candles = 46.452
Result: 500 lux ≈ 46.45 foot-candles
A US plan calls for 50 foot-candles. Convert it to lux.
- Use lux = foot-candles x 10.7639
- lux = 50 x 10.7639
- lux = 538.195
Result: 50 foot-candles ≈ 538.20 lux
An old meter reads 0.2 phot. Convert it to lux and foot-candles.
- lux = phot x 10000 = 0.2 x 10000 = 2000 lux
- foot-candles = 2000 / 10.7639 = 185.81 fc
Result: 0.2 phot = 2000 lux ≈ 185.81 foot-candles
A security camera needs a minimum of 0.5 lux to work at night, and a floodlight test reads 6 foot-candles in the yard.
- Use lux = foot-candles x 10.7639
- lux = 6 x 10.7639
- lux = 64.58
Result: 6 foot-candles ≈ 64.58 lux, well above the 0.5 lux camera minimum
Illuminance unit conversion factors (relative to lux)
| Unit | Symbol | Value in lux |
|---|---|---|
| Lux | lx | 1 |
| Foot-candle | fc | 10.7639 |
| Phot | ph | 10000 |
| Kilolux | klx | 1000 |
| Nox | nx | 0.001 |
| Lumen per square metre | lm/m² | 1 |
| Lumen per square foot | lm/ft² | 10.7639 |
Typical illuminance levels for common situations
| Situation | Lux | Foot-candles |
|---|---|---|
| Starlit night, no moon | 0.001 | 0.0001 |
| Moonlit night | 1 | 0.09 |
| Living room | 50 | 4.6 |
| Office or classroom | 300 to 500 | 28 to 46 |
| Detailed bench work | 1000 | 93 |
| Overcast daylight | 1000 to 10000 | 93 to 929 |
| Direct sunlight | 32000 to 100000 | 2973 to 9290 |
Recommended lux levels by task (general guidance, check local codes)
| Task or area | Lux | Foot-candles |
|---|---|---|
| Corridors, warehouses, storage | 100 to 200 | 9 to 19 |
| Retail floor, general office | 300 to 500 | 28 to 46 |
| Classrooms, reading areas | 300 to 500 | 28 to 46 |
| Detailed technical drawing | 750 to 1000 | 70 to 93 |
| Fine assembly or inspection work | 1000 to 1500 | 93 to 139 |
| Security camera minimum (typical spec) | 0.5 to 1 | 0.05 to 0.09 |
Common mistakes to avoid
- Mixing up lux and lumens. Lumens measure the total light a source emits, while lux measures how much of that light lands on a surface. A bright bulb (high lumens) can still give low lux on a wall if the wall is far away or the light is spread out.
- Using the wrong conversion direction. Lux numbers are larger than foot-candle numbers for the same light level, because a square metre is bigger than a square foot. If your converted value looks roughly ten times too big or small, you have applied the factor the wrong way.
- Confusing illuminance with luminous intensity. Candela measures light from a source in a direction, not light arriving on a surface. You cannot convert candela directly to lux without knowing the distance, so do not treat them as interchangeable.
- Rounding 10.7639 too early. Using a rough 10 or 10.76 instead of 10.7639 introduces small errors that grow with large readings. This converter keeps full precision and rounds only the displayed result.
- Assuming lux converts directly to watts. Lux measures visible light weighted by human eye sensitivity, not raw radiant power. Two bulbs with the same wattage can produce very different lux, so there is no single lux-to-watts factor without knowing the light source.
- Ignoring distance for point-source readings. Illuminance from a point source falls off with the square of distance (the inverse-square law), so a lux reading taken close to a lamp will not match a reading taken further away, even though the source has not changed.
Glossary
- Illuminance
- The amount of luminous flux falling on a surface per unit area, measured in lux or foot-candles.
- Lux (lx)
- The SI unit of illuminance, equal to one lumen per square metre.
- Foot-candle (fc)
- An imperial unit of illuminance equal to one lumen per square foot, about 10.7639 lux.
- Phot (ph)
- A CGS unit of illuminance equal to one lumen per square centimetre, or 10,000 lux.
- Nox (nx)
- A unit for very low illuminance equal to one thousandth of a lux, used for night-vision and low-light camera specs.
- Lumen (lm)
- The SI unit of luminous flux, the total visible light emitted by a source.
- Candela (cd)
- The SI unit of luminous intensity, describing light emitted from a source in a given direction, not light landing on a surface.
- Inverse-square law
- The rule that illuminance from a point source falls to one quarter when the distance from the source doubles.
Frequently asked questions
How many lux are in a foot-candle?
One foot-candle equals exactly 10.7639 lux. That factor is the number of square feet in one square metre, since lux is lumens per square metre and a foot-candle is lumens per square foot. To go from foot-candles to lux, multiply by 10.7639.
How do I convert lux to foot-candles?
Divide the lux value by 10.7639. For example, 500 lux / 10.7639 is about 46.45 foot-candles. This converter does it instantly when you type a value into the lux box.
What is the difference between lux and lumens?
Lumens measure the total light a source emits in all directions. Lux measures how much of that light actually lands on a surface, equal to lumens per square metre. A source with high lumens can still give low lux if the light is spread over a large area.
What is a phot?
A phot is an older CGS unit of illuminance equal to one lumen per square centimetre. Because one square metre contains 10,000 square centimetres, one phot equals 10,000 lux. It is rarely used today but appears on some legacy instruments.
How much illuminance is daylight?
Full daylight without direct sun is roughly 10,000 to 25,000 lux (about 930 to 2,320 foot-candles), and direct sunlight can exceed 100,000 lux. Indoor office lighting is usually only 300 to 500 lux by comparison.
Is lux the same as lumen per square metre?
Yes. One lux is defined as exactly one lumen per square metre, so the two are identical. The lumen per square foot is the foot-candle, which is about 10.7639 lux because a square metre is larger than a square foot.
How do I convert lumens to lux?
You cannot convert lumens to lux with a fixed factor alone, because lux depends on the area the light covers: lux = lumens divided by area in square metres. A 1,000 lumen bulb gives 1,000 lux spread over one square metre, but only about 111 lux spread over nine square metres. Always divide by the illuminated area rather than looking for a single conversion number.
Can you convert lux to watts?
Not directly. Lux measures visible light weighted by how sensitive the human eye is to different colours, while watts measure raw radiant power across the whole spectrum. An LED, an incandescent bulb and sunlight all convert watts to lux differently, so there is no universal lux-to-watts factor.
What is a nox and when is it used?
A nox is a very small unit of illuminance equal to one thousandth of a lux (1 nox = 0.001 lux). It is used for extremely low light levels, such as specifying the sensitivity of night-vision equipment or security cameras that need to operate in near total darkness.
Does illuminance change with distance from a light source?
Yes. For a point source such as a bulb, illuminance follows the inverse-square law: doubling the distance from the source cuts the illuminance to a quarter. A lux reading is only valid at the exact point and distance where it was measured, so readings can vary a lot across a room.