Actually, footcandles and lux are not units of Luminance, but rather units of Illuminance.
There are four main measurements of photometry:
-Lumens: Total Power of Light (weighed to human eye response) that a light gives off. [lumen]
-Candelas: Total Intensity (Luminous Flux) given off PER solid angle. [cd or lumens/steradian]
-Illuminance: Total Power Incident on the surface of a square meter. [lumens/m2 or LUX]
-Luminance: Total Intensity per Solid Angle from a light with a given size. [cd/m2]
Footcandles are the US (read non-metric) version of Illuminance, measured in lumens/ft2.
Footlamberts are the US version of Luminance, IF the luminance is measured from a Lambertian (perfectly diffusing) Surface. This does not readily apply to screens with gain other than 1.0. Often cosine falloff adjustments are needed for the proper interpretation of the levels read.
Incident Light Meters give you an exposure for a surface that would be a given percentage of the light incident. Often this percentage is erroneously called 18%, but to find the actual percentage you plug in this equation for the meter's calibration constants ( [K*PI/C] ). Sekonic gives you readings for 15.7% on the incident meter, for instance. What this translates into on your camera is dependent on the ISO speed and manufacturer's deviations, of course.
Footcandles, Lux, Foot Lambert, and cd/m² are great for the reasons listed above and serve to give you "absolute values" of the scene, etc. EV, Aperture Priority, Shutter Priority and camera-centric values give you "relative values" to a given meter and camera calibration.