Conversion Equation

Where 'r' is the radius of the sphere in feet.

In case, If you would like to use meters instead of feet, then convert sq. feet to sq. meter.

ie; 1 sq. mt. = 10.76391 sq. ft. 

Lumen

Lumen is the SI unit of Luminous Flux. It indicates the total amount of visible light emitted from a source.

Luminous Flux / Luminous Power is the amount of light energy radiated from a source in all directions per second and is denoted as F.

Lux

Lux (lx) is the SI unit of illumination. It indicates the illumination intensity of an area.

One Lux is equal to One Lumen per square meter.

illuminance (Ev) is the amount of luminous flux per unit area.