Theater Calculators

Screens & projection

Projector Brightness (Foot-Lamberts) Calculator

Foot-lamberts = lumens × gain / area in square feet. Cinema SDR sits near 14–16 fL; living-room HDR wants more. High gain helps and hurts viewing angle.

Inputs

Units
lm

1.0 matte white; ALR often 0.6–1.2 on-axis.

m
m

Results

Image area
3.95m²
Foot-lamberts
58.8fL
Nits
201.5cd/m²

The Result is indicative and educational. It does not constitute a design, a technical opinion or medical advice and does not replace calculations or verification by a person with the appropriate qualifications and authorisations. Before purchase, installation or use in practice – in particular in electrical installations – the Result should be verified by a qualified specialist. Details: Terms of Service, point 4.

Example products

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Calculation method

fL = (Φ × G) / A_ft². Nits ≈ fL × 3.426. Area comes from width × height.

Exact formula

A_ft² = W·H·10.764. fL = lumens·gain / A_ft². Limits: centre-screen, no ANSI checkerboard, no lamp age, no HDR tone-map.

Frequently asked questions

How many foot-lamberts for HDR?

Consumer HDR highlights want far more than 16 fL. Treat this as SDR cinema math, then add headroom for HDR tone-mapping.

Does ALR lower fL?

On-axis gain can be near 1.0; off-axis it drops. This tool is on-axis only.

Lux or foot-lamberts?

Lux is the light landing on the screen, in lumens per square metre. Foot-lamberts and nits are the light coming back off it after gain, which is what your eye sees. This tool reports the second.

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