Photometric formulas:
 

Luminous intensity I	Luminous flux in solid angle Solid angle	I [cd] =  F [lm] w [sr]
Luminous flux F	Luminous intensity x solid angle	F [lm] =  I [cd] x w [sr]
Illuminance E	luminous flux  =  luminous intensity illuminated area square of the distance	E [lx] =  F [lm]  =  I [cd] A [m2] d2 [m2]
Luminance L	luminous intensity observed illuminated area	L [cd/m2] =  I [cd] A [m2]
Luminous efficacy h	luminous flux consumed power	h [lm/W] =  F [lm] P [W]

 
There are 4p solid angles (sr) in a full sphere. A solid angle of 1 sr corresponds to circular cone with an apex angle of 65,6 °.