Luminance converter

Luminance is referenced to candela per square meter (cd/m²), and the first thing worth knowing is that "nit," the unit TV and monitor marketing loves, is exactly the same unit under a different name — the factor between them is 1, not a rounding coincidence. Stilb (candela per square centimeter) scales that up by ten thousand for very bright, small sources, while candela per square foot and candela per square inch simply swap in imperial area.

The featured pair is candela per square meter to foot-lambert: fL = cd/m² × 0.291863508, with the reverse direction multiplying by 3.4262591.

A typical laptop display running at 300 cd/m² (300 nits) converts to 300 × 0.291863508 = 87.5590524 fL. A bright HDR television peaking at 1,000 nits converts to 1,000 × 0.291863508 = 291.863508 fL, illustrating just how much brighter modern HDR panels can get compared with older displays and the cinema-screen standards foot-lamberts were originally built around.

Luminance is the number display makers, cinema projectionists, and lighting designers all live by: monitor and phone marketing specs brightness in nits (cd/m²), movie theaters still target screen luminance in foot-lamberts under long-standing projection standards, automotive designers check dashboard and instrument-cluster luminance for daylight readability, and photometric engineers use candela per square meter when modeling how bright a surface appears under a given lighting design.

Because nit and cd/m² are identical, no actual conversion is needed between them — the confusion is just that two different industries picked two different names for the same thing. The real pitfall sits with the lambert-family units (lambert, millilambert, foot-lambert, apostilb, blondel): each bakes in a factor derived from the Lambertian (perfectly diffuse) reflection model, which involves π, so their conversion factors to cd/m² come out as long, non-round decimals like 3183.098861837907 rather than anything you could estimate mentally.