Illuminance Converter

1. Enter the value you want to convert.
2. Choose the from unit.
3. Choose the to unit.
4. Read the result and the conversion rate.

Here is what each result means:

Illuminance is how much light falls on a surface, spread over its area. The SI unit is the lux, which is one lumen of light per square metre. A well-lit office is around 500 lux, an overcast day outdoors is a few thousand lux, and direct sunlight can exceed 100,000 lux. It measures light arriving at a surface, not the brightness a surface appears to give off.

The main alternative is the foot-candle, still common in North American lighting design. It is one lumen per square foot, and because a square foot is smaller than a square metre, one foot-candle equals about 10.76 lux. The phot and milliphot come from the older centimetre-gram-second system, where a phot is one lumen per square centimetre, a very intense 10,000 lux. The nox is a tiny unit used for very low light.

This converter bridges every unit through the lux. It multiplies your value by the number of lux in its unit, then divides by the number in the target unit. Because each unit has a fixed value, the conversions are exact and never change.

Illuminance should not be confused with luminance or with luminous flux. Flux, in lumens, is the total light a source emits. Illuminance, in lux, is how much of that light lands on a given area. This converter deals only with illuminance units.

It converts through the lux, the SI unit of illuminance.

1. Your value is multiplied by its unit's value in lux.
2. That gives the illuminance in lux, the common base.
3. Dividing by the target unit's value gives the result.

For related quantities, see the power converter and the energy converter.

Convert 500 lux to foot-candles.

Result: 500 lux is about 46.45 fc, since one foot-candle is 10.76 lux. That is a typical office light level, whichever unit a lighting standard happens to use.

Every unit has a fixed value in lux.

The phot is a large unit, at 10,000 lux, so it suits intense light, while the nox at one thousandth of a lux is for very dim conditions such as moonlight. The foot-candle sits close to 10.76 lux, a factor worth remembering when reading lighting standards.

Illuminance spans a huge range, from moonlight to direct sun.

Comparing settings this way shows why lighting design uses these units. A workspace standard might call for 500 lux, or about 46 foot-candles, and the converter lets you move between whichever unit a local code or datasheet uses.

The Two Units

The ratio between the from-unit and to-unit sets the result; each has a fixed value in lux.

Area Basis

The foot-candle uses a square foot and the lux a square metre, which gives the 10.76 factor.

The Size of the Unit

A large unit like the phot gives small numbers, while a tiny one like the nox gives large ones.

Lighting Design

Convert between lux and foot-candles when following a lighting standard or code.

Photography

Compare a metered light level in lux with foot-candle references.

Older References

Turn a phot or milliphot figure from an older text into modern lux.

1. Confusing Lux and Lumens

Lumens measure total light output; lux measures light per square metre landing on a surface.

2. Mixing Lux and Foot-candles

They are not equal. One foot-candle is about 10.76 lux, a factor easy to drop.

3. Confusing Illuminance with Luminance

Illuminance is light arriving on a surface; luminance is light leaving one toward the eye.

4. Wrong Direction

Check which unit is the from and which is the to; swapping them inverts the result.

5. Forgetting the Phot Scale

A phot is 10,000 lux, so a small phot value is a very bright light.

Conversions use fixed factors relative to the lux.

About 10.76 lux. A foot-candle is one lumen per square foot, and a square foot is smaller than a square metre, so it packs the same lumen into less area.

Divide lux by about 10.76. So 500 lux is about 46.5 foot-candles. To go the other way, multiply foot-candles by 10.76.

Lumens measure the total light a source gives out. Lux measures how much of that light falls on each square metre of a surface.

A phot is a light level of one lumen per square centimetre, equal to 10,000 lux. It comes from the older centimetre-gram-second system and is now rare.

Around 500 lux, or about 46 foot-candles. Detailed tasks may call for 750 to 1,000 lux, while a corridor may need only 100 lux.

Roughly 100,000 lux, or about 9,300 foot-candles. An overcast day is far dimmer, at around 1,000 lux.

No. Illuminance in lux is light arriving on a surface. Luminance, in candela per square metre, is light leaving a surface toward the eye.

A nox is a very small unit of illuminance equal to one thousandth of a lux. It is used for very low light levels, such as moonlight.

No. The calculation runs in your browser and nothing you enter is stored or sent anywhere, unless you choose Save, which keeps the result only on this device.

• Lux (Wikipedia).
• Foot-candle (Wikipedia).
• Illuminance (Wikipedia).