The luminance of a perfect Lambertian diffuse reflecting surface in foot-lamberts is equal to the incident illuminance in foot-candles.
For real diffuse reflectors, the ratio of luminance to illuminance in these units is roughly equal to the reflectance of the surface.
The foot-lambert is also used in the flight simulation industry to measure the highlight brightness of visual display systems.
The minimum required highlight brightness varies based on the type and level of Flight Simulation Training Device (FSTD), but is generally 3–6 foot-lamberts for most devices qualified under Federal Aviation Administration (FAA) or Joint Aviation Authorities (JAA) regulations.
[1][2][3] Military specifications for illuminated switches, panels, and displays, such as MIL-PRF-22885 and SAE AS7788, also require luminance measurements in foot-lamberts.