Foot-Lambert calculator

is a unit of luminance (the intensity of light emitted from a surface). It is the luminance of a perfectly diffusing surface emitting or reflecting 1 lumen per square foot. This unit is used in the US and Canada, and worldwide in the cinema business.
     To calculate from screen dimensions, click here

Luminance conversion

4 cd/m2
Candela per square meter
4 cd/m2
Candela per square foot
0.3716 cd/sq.ft.
Stilb (CGS)
0.0004 Stilb
Apostilb (blondel)
1.27 Apostilb
0.000127 Lambert
1.1675 ftL
Exposure Value
5 EV

Screen luminance: EV5

-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


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.