Foot-lambert calculator

Foot-lambert is a unit of luminance. It is the luminance of a perfectly diffusing surface emitting or reflecting one lumen per square foot. This unit is used in the US and Canada, and worldwide in the cinema business.

     To directly input luminance values, click here

Foot-Lambert: 16.5fL

     Diagonal = 25 meter (m)
     ⇒ screen height = 9.79 meter (m), screen width = 23 meter (m)
     ⇒ screen area = 225.2 square meter (m)
     Diagonal = 82 feet (ft)
     ⇒ screen height = 32.1 feet (ft), screen width = 75.5 feet (ft)
     ⇒ screen area = 2424 square feet (ft)
     Luminance = 16.5 fL (foot-lambert)
     Acceptable for rooms with little ambient light. E.g. cinema screens aim for 14-16 ftL.
     Luminance = 56.5 cd/m2 (candela/square meter or nit)
     8.82 EV (exposure value)

Screen luminance: EV8.82

-5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
starlight to dim ambient lightmoon eclipse to night home interiorneon lights to landscape after sunsetbright light to weak sunbright daylight to direct sunlight

Explanation

A foot-lambert or footlambert (ftL, sometimes fl or ft-L) is a unit of luminance. For screens that are projected upon (like cinema, home cinema), it quantifies how much light is reflected (to the center of the room). This depends on the amount of light produced (lumens), the size of the screen and the screen gain.

Examples

Cinema: 32000 lumen on 23x10m screen

References

Foot-lambert
Lambert
Screen gain