Convert luminance units — candela/m², nit, stilb, foot-lambert and more.
| Unit | Name | Value |
|---|---|---|
| nt | Nit | 1 |
| sb | Stilb | 0.0001 |
| L | Lambert | 0.00031415915 |
| fL | Foot-lambert | 0.29186343 |
| cd/ft² | Candela/Square Foot | 0.09290313 |
| cd/in² | Candela/Square Inch | 0.00064516129 |
Formula: Foot-Lambert = Candela/m² × 0.2919
Multiply any Candela/m² value by 0.2919 to get Foot-Lambert.
Reverse: Candela/m² = Foot-Lambert × 3.426
Common luminance values — factor: 1 cd/m² = 0.2919 fL
| Candela/m² (cd/m²) | Foot-Lambert (fL) | Context |
|---|---|---|
| 0.001 cd/m² | 0.0002919 fL | Moonlit night sky |
| 0.1 cd/m² | 0.02919 fL | Overcast sky |
| 1 cd/m² | 0.2919 fL | Candle flame |
| 10 cd/m² | 2.919 fL | Very dim display |
| 50 cd/m² | 14.59 fL | Dark room display |
| 100 cd/m² | 29.19 fL | SDR reference white |
| 200 cd/m² | 58.37 fL | Typical office monitor |
| 500 cd/m² | 145.9 fL | Bright monitor |
| 1000 cd/m² | 291.9 fL | HDR10 peak |
| 2000 cd/m² | 583.7 fL | iPhone peak outdoor |
| 5000 cd/m² | 1459 fL | Dolby Vision phone |
| 1e+04 cd/m² | 2919 fL | Automotive HUD |
| 1e+05 cd/m² | 2.919e+04 fL | Direct sunlight |
| 1e+06 cd/m² | 2.919e+05 fL | Arc lamp |
| 1.600e+09 cd/m² | 4.67e+08 fL | Sun surface |
cd/m² ÷ 3.426 = fL.
48 cd/m² = 14 fL (SMPTE). 3.426 cd/m² = 1 fL.
fL × 3.426 = cd/m².
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.
Candela per square meter (cd/m²) is the SI unit of luminance, measuring the intensity of light emitted from a surface per unit area per steradian. It is identical to the nit (nt) in value and replaced the older photometric units in the International System of Units adopted in 1979.
cd/m² is the universal unit in display technology and lighting engineering. Computer monitors: 200–350 cd/m²; smartphone screens: 600–2,000 cd/m²; the sun's surface: about 1.6 × 10⁹ cd/m². SDR content is mastered at 100 cd/m²; HDR10 peaks at 1,000–10,000 cd/m².
Interesting fact: The minimum luminance the human eye can detect is about 10⁻⁶ cd/m² (starlight). The maximum comfortable luminance for sustained viewing is about 1,000 cd/m². The Sun at midday has a luminance of approximately 1.6 billion cd/m².
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 cd/m² = 0.2919 fL. Reverse: 1 fL = 3.426 cd/m².
All conversions use IEEE 754 double-precision arithmetic, accurate to at least 8 significant figures.