Video and displays
Foot-lambert (fL)
A unit of screen luminance used for projection, equal to 3.426 nits, with 16 fL as the SMPTE reference for a dark cinema.
A foot-lambert describes how bright the image on a projection screen appears after the projector's lumens have been spread over the screen area and modified by screen gain.
Projection is reflective, so the same projector looks dimmer on a bigger screen. Working in foot-lamberts lets you compare screen sizes, lamp modes, and gains on one scale and tells you when a screen is too large for the projector driving it.
SMPTE specifies 16 fL for cinema, and 12 to 22 fL is comfortable at home for SDR. Estimate it as (lumens x gain) / screen area in square feet: 1,500 lumens on a 1.0 gain 100 inch screen (about 29.7 sq ft) gives roughly 50 fL, leaving headroom for lamp aging and eco mode.
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