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/in² = Foot-Lambert × 0.00221
Multiply any Foot-Lambert value by 0.00221 to get Candela/in².
Reverse: Foot-Lambert = Candela/in² × 452.4
Common luminance values — factor: 1 fL = 0.00221 cd/in²
| Foot-Lambert (fL) | Candela/in² (cd/in²) | Context |
|---|---|---|
| 0.001 fL | 2.210e-06 cd/in² | Dark |
| 0.01 fL | 2.210e-05 cd/in² | Very dim |
| 0.1 fL | 0.000221 cd/in² | Dim |
| 1 fL | 0.00221 cd/in² | 3.43 nit |
| 2 fL | 0.004421 cd/in² | 6.85 nit |
| 5 fL | 0.01105 cd/in² | 17 nit |
| 14 fL | 0.03095 cd/in² | SMPTE cinema 48 nit |
| 31 fL | 0.06853 cd/in² | HDR cinema 106 nit |
| 50 fL | 0.1105 cd/in² | 171 nit |
| 100 fL | 0.221 cd/in² | TV studio 343 nit |
| 200 fL | 0.4421 cd/in² | 685 nit |
| 500 fL | 1.105 cd/in² | 1,713 nit |
| 1000 fL | 2.21 cd/in² | 3,426 nit |
| 1e+04 fL | 22.1 cd/in² | 34,260 nit |
| 1e+05 fL | 221 cd/in² | 342,600 nit |
1 fL = 0.00221 cd/in².
nit = cd/m² exactly. Use this as the bridge between SI and legacy units.
Multiply result by 452.4 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 inch (cd/in²) is used in display engineering and high-brightness projector specifications where cd/m² values would be inconveniently large. One cd/in² = 1,550 cd/m².
Very high-brightness applications use cd/in²: aviation cockpit displays, outdoor digital signage, and laser projectors for cinema and simulation. A 10,000 nit HDR display = 6.45 cd/in²; a cinema laser projector at 60,000 lumens might achieve 20+ cd/in² on a small screen.
Interesting fact: Military aircraft cockpit displays must remain readable in direct sunlight (approximately 10,000 cd/m² ambient). Modern night-vision-compatible displays adjust from <0.001 cd/in² (night mode) to >6 cd/in² (day mode) — a range of over 6 million to one.
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 = 0.00221 cd/in². Reverse: 1 cd/in² = 452.4 fL.
All conversions use IEEE 754 double-precision arithmetic, accurate to at least 8 significant figures.