Illuminance and Luminance Converter
Convert lighting units with the factor behind each answer. Illuminance, luminance and luminous intensity are three different quantities.
1 lx = 0.09290304 fc
Common conversions
Three different quantities
Illuminance (lux) is light arriving on a surface. Luminance (cd/m²) is the brightness of a surface or source seen from a direction. Luminous intensity (cd) is the light emitted in one direction by a source. They cannot be converted into each other with a fixed factor.
Foot-candle and foot-lambert
One foot-candle is one lumen per square foot, about 10.764 lux. One foot-lambert is 1/π candela per square foot, about 3.426 cd/m². Airfield sign luminance may be quoted in cd/m² or in foot-lamberts, depending on the standard, so convert before comparing a measurement with a requirement.
Luminous intensity
Airfield light intensities are given in candela, often in kcd for approach lights. Intensity is measured on the beam, so it is not the same as the lux on the ground.
Unit factors
Every unit in terms of the base unit shown. To convert, multiply by the factor of the unit you have and divide by the factor of the unit you want.
Illuminance units
| Unit | Equals | What it is |
|---|---|---|
| lx | 1 lx | Lux: one lumen per square metre. The SI unit of illuminance. |
| klx | 1,000 lx | Kilolux, a thousand lux. |
| fc | 10.76391042 lx | Foot-candle: one lumen per square foot, about 10.764 lux. |
| phot | 10,000 lx | Phot, the CGS unit: 10,000 lux. |
Luminance units
| Unit | Equals | What it is |
|---|---|---|
| cd/m² | 1 cd/m² | Candela per square metre (nit). The SI unit of luminance. Sign and display brightness. |
| kcd/m² | 1,000 cd/m² | Kilocandela per square metre. |
| cd/ft² | 10.76391042 cd/m² | Candela per square foot. |
| fL | 3.4262591 cd/m² | Foot-lambert, 1/π candela per square foot. Older US practice for sign and display luminance. |
| sb | 10,000 cd/m² | Stilb, the CGS unit: 10,000 cd/m². |
Luminous intensity units
| Unit | Equals | What it is |
|---|---|---|
| mcd | 0.001 cd | Millicandela. LED indicators. |
| cd | 1 cd | Candela, the SI unit of luminous intensity. |
| kcd | 1,000 cd | Kilocandela. Airfield light peak intensities are often quoted in cd or kcd. |
Conversion pages
Frequently asked questions
What is the formula to convert lx to fc?
fc = lx × 0.09290304. For example, 500 lx is 46.45152 fc.
How do I convert fc back to lx?
lx = fc × 10.76391042. The Swap button above reverses the direction for any pair of units.
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