Thanks for the reply.
Interesting. So it seems footcandles/lux are used when you want to express a "fixed" unit of incident light measurement, but regardless of any other factors.
The other two guys, foot lamperts & cd/m², also measure with a "fixed" unit of light but they measure reflectived light (or light being emitted by a particular object). And since we measure with "m²" that also is typically used outside the U.S.
I guess they are just an extension to the idea of incident and reflective light measurement.
Please let me know if I'm wrong! Other than that, splendid! Thanks for the reply.