Illumination Calculations

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One lux is equal to one lumen per square metre, where 4π lumens is the total luminous flux of a light source of one candela of luminous intensity:

1 lx = 1 lm·m^-2 = 1 cd·sr·m^–2.

To be simple,

A bulb of 1 candela will give out an illumination energy of 1 lumen per st-radian ie total energy output of this bulb is 4π Steradians.

If this amount of light falls on an 1 sq meter area then that area will be lit by a lux illumination.

In fact if you want it to be simple, then the definition of steradian is the solid (conical) angle subtended by the surface of the sphere whose area is r²

if r=1 then the area too is 1 so one cd source will illuminate a surface (spherical) at 1 m from the source to 1 lux illumination. (this will bypass the lumen )