Convert luminance units — candela/m², nit, stilb, foot-lambert and more.
| Unit | Name | Value |
|---|---|---|
| cd/m² | Candela/Square Meter | 3.42626 |
| nt | Nit | 3.42626 |
| sb | Stilb | 0.000342626 |
| L | Lambert | 0.0010763909 |
| cd/ft² | Candela/Square Foot | 0.31831028 |
| cd/in² | Candela/Square Inch | 0.0022104903 |
Formula: Candela/ft² = Foot-Lambert × 0.3183
Multiply any Foot-Lambert value by 0.3183 to get Candela/ft².
Reverse: Foot-Lambert = Candela/ft² × 3.142
Common luminance values — factor: 1 fL = 0.3183 cd/ft²
| Foot-Lambert (fL) | Candela/ft² (cd/ft²) | Context |
|---|---|---|
| 0.001 fL | 0.0003183 cd/ft² | Dark |
| 0.01 fL | 0.003183 cd/ft² | Very dim |
| 0.1 fL | 0.03183 cd/ft² | Dim |
| 1 fL | 0.3183 cd/ft² | 3.43 nit |
| 2 fL | 0.6366 cd/ft² | 6.85 nit |
| 5 fL | 1.592 cd/ft² | 17 nit |
| 14 fL | 4.456 cd/ft² | SMPTE cinema 48 nit |
| 31 fL | 9.868 cd/ft² | HDR cinema 106 nit |
| 50 fL | 15.92 cd/ft² | 171 nit |
| 100 fL | 31.83 cd/ft² | TV studio 343 nit |
| 200 fL | 63.66 cd/ft² | 685 nit |
| 500 fL | 159.2 cd/ft² | 1,713 nit |
| 1000 fL | 318.3 cd/ft² | 3,426 nit |
| 1e+04 fL | 3183 cd/ft² | 34,260 nit |
| 1e+05 fL | 3.183e+04 cd/ft² | 342,600 nit |
1 fL = 0.3183 cd/ft².
nit = cd/m² exactly. Use this as the bridge between SI and legacy units.
Multiply result by 3.142 to recover the original fL 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 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.
Candela per square foot (cd/ft²) is an Imperial luminance unit equal to approximately 10.764 cd/m². It is used in US lighting engineering for specifying surface luminance of illuminated panels, signage, and architectural lighting elements.
Architectural lighting specifications in North America sometimes use cd/ft² for luminaire surface luminance limits (to control glare) and for evaluating light trespass onto adjacent properties. Exit signs and emergency lighting luminance requirements may be stated in cd/ft².
Interesting fact: The difference between cd/ft² and foot-Lamberts reflects whether the surface is treated as a perfect diffuser: 1 fL = (1/π) cd/ft², while 1 cd/ft² = π fL. The distinction matters for calculating luminance of non-Lambertian (specular or textured) surfaces.
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 fL = 0.3183 cd/ft². Reverse: 1 cd/ft² = 3.142 fL.
All conversions use IEEE 754 double-precision arithmetic, accurate to at least 8 significant figures.