Nits and foot-lamberts on screen
Estimated on-screen brightness for a given lumen figure, screen size and gain.
- Unit
- cd/m² (nits)
- Standard
- Physics: L = Φ × gain ÷ (π × A)
- ISO 21118
- Extension
- Better
- ↑ Higher
- Screen
- 2.21 × 1.25 m
- 2.76 m²
- Luminance
- 231 cd/m²
- Foot-lamberts
- 67.4 fL
- vs 14 fL cinema
- 481 %
Show the numbers
| ST 431-1 · 14 fL | SMPTE ST 431-1:2006 digital cinema, 48.0 cd/m² nominal |
|---|---|
| SMPTE 196M · 16 fL | SMPTE 196M film projection, open gate, 16 fL ≈ 55 cd/m² |
| 30 fL | Upper end of the 16–30 fL home-theatre SDR range in our glossary |
| PQ max | SMPTE ST 2084 PQ signal range tops out at 10,000 cd/m² |
| Formula | L = lumens × gain ÷ (π × area m²); 1 fL = 3.426 cd/m² |
Idealised: uses the full rated lumens, a Lambertian-equivalent gain and no ambient light, so real measured nits will be lower. Dashed lines are published reference levels (see the numbers). The 30 fL line is the top of our glossary's 16–30 fL home-theatre range, not a standard.
How to compare it
Screen luminance (derived)(cd/m² (nits))
The only brightness that matters to the viewer. Target references: SMPTE ST 431-1 cinema = 48 cd/m² (14 fL). Home SDR and HDR targets are higher, with ambient light raising the requirement.
Target screen luminance(cd/m²)
The luminance we aim for at the screen.
Cinema reference is 48 cd/m² (14 fL). Dark home cinemas run brighter for SDR, rooms with ambient light need far more, and HDR wants as much as possible.
Standard: SMPTE ST 431-1 (48 cd/m², DCI)
Marketing traps
- Screen luminance (derived): This holds only for a Lambertian screen with an on-axis viewer. ALR and high-gain screens break the simple formula.
Deep cut
Screen luminance (derived). 1 fL = 3.426 cd/m². For 100″ 16:9 (≈2.76 m²) at gain 1.0 with 1,500 calibrated lm, the screen shows ≈173 nits (≈50 fL). HDR mastering targets of 1,000–4,000 nits are why projector HDR is all about tone mapping.
Target screen luminance. Pair it with `derived.screen_luminance_nits` to say 'this projector reaches X fL on your 120″ screen in calibrated mode' for each model.