Convert luminance units — candela/m², nit, stilb, foot-lambert and more.
| Unit | Name | Value |
|---|---|---|
| cd/m² | Candela/Square Meter | 3183.1 |
| nt | Nit | 3183.1 |
| sb | Stilb | 0.31831 |
| fL | Foot-lambert | 929.03049 |
| cd/ft² | Candela/Square Foot | 295.71995 |
| cd/in² | Candela/Square Inch | 2.0536129 |
Formula: Foot-Lambert = Lambert × 929
Multiply any Lambert value by 929 to get Foot-Lambert.
Reverse: Lambert = Foot-Lambert × 0.001076
Common luminance values — factor: 1 L = 929 fL
| Lambert (L) | Foot-Lambert (fL) | Context |
|---|---|---|
| 0.001 L | 0.929 fL | Dark |
| 0.01 L | 9.29 fL | Very dim |
| 0.1 L | 92.9 fL | Dim |
| 0.314 L | 291.7 fL | 1 nit |
| 1 L | 929 fL | 3.18 nit |
| 3.14 L | 2917 fL | 10 nit |
| 10 L | 9290 fL | 32 nit |
| 31.4 L | 2.917e+04 fL | 100 nit SDR |
| 100 L | 9.29e+04 fL | 318 nit |
| 314 L | 2.917e+05 fL | 1,000 nit HDR |
| 1000 L | 9.29e+05 fL | 3,183 nit |
| 3183 L | 2.957e+06 fL | ~1 sb |
| 3.183e+04 L | 2.957e+07 fL | 10,000 nit |
| 1e+06 L | 9.29e+08 fL | 3.14 Mnit |
| 5e+08 L | 4.645e+11 fL | Sun |
1 L = 929 fL.
nit = cd/m² exactly. Use this as the bridge between SI and legacy units.
Multiply result by 0.001076 to recover the original L value.
Specifies monitor, TV, and smartphone panel brightness in nits (cd/m²) for HDR grading and product specs.
Calibrates projector output to SMPTE standard of 14 foot-Lamberts for optimal image quality.
Calculates luminance of illuminated surfaces in cd/m² to evaluate glare and visual comfort.
Designs head-up displays exceeding 10,000 nits for daylight readability.
Converts between legacy (Lambert, stilb) and SI (cd/m²) units when reviewing historical data.
Specifies outdoor LED sign brightness in nits for visibility across ambient lighting conditions.
The Lambert (L) is a CGS unit of luminance equal to 1/π candela per square centimeter ≈ 3,183 cd/m². It was defined by the German mathematician Johann Heinrich Lambert, whose work on photometry in the 1760s established the foundations of the science.
The Lambert was the standard photometric unit in North American optical engineering through the mid-20th century. Film screen luminance was specified in Lamberts; the SMPTE standard for cinema projection is 14 foot-Lamberts ≈ 48 cd/m².
Interesting fact: The Lambert is defined using 1/π because a perfectly diffuse (Lambertian) surface reflecting 1 lumen per cm² has a luminance of exactly 1/π cd/cm². This mathematical convenience made it the natural unit for Lambertian radiators.
The foot-Lambert (fL) is the US customary unit of luminance equal to 1/π candela per square foot ≈ 3.426 cd/m². It replaced the Lambert for cinema and television applications in North America and remains the standard in US projection specifications.
The film industry uses foot-Lamberts universally in North America: SMPTE specifies cinema screens at 14 fL (±3 fL); HDR cinema (Dolby Vision) targets 31 fL; 3D projection requires higher gain screens to compensate for dimming. Television studio monitors have been calibrated to 100 fL historically.
Interesting fact: The 14 fL standard for cinema projection was chosen in the 1950s as a compromise between image brightness and lamp lifetime. Modern laser projectors can maintain 14 fL throughout their lifetime, unlike xenon lamps which dim with age.
Luminance measures how bright a surface appears to a human observer. The SI unit is cd/m² (identical to the nit used in display industry). Older units — Lambert, foot-Lambert, and stilb — remain in cinema, photometry, and legacy specs. Key anchors: 100 cd/m² = SDR reference; 1,000 cd/m² = HDR10 peak; 14 fL = 48 cd/m² = SMPTE cinema standard.
Exact factor: 1 L = 929 fL. Reverse: 1 fL = 0.001076 L.
All conversions use IEEE 754 double-precision arithmetic, accurate to at least 8 significant figures.