Photometric formulas
| Luminous intensity I |
| Luminous flux in solid angle |
| Solid angle |
|
|
| Luminous flux Ф |
Luminous intensity x solid angle |
|
| Illuminance E |
| luminous flux |
= |
luminous intensity |
| illuminated area |
square of the distance |
|
| E [lx] = |
Ф [lm] |
= |
I [cd] |
| A [m2] |
a2 [m2] |
|
| Luminance L |
| luminous intensity |
| observed illuminated area |
|
| L [cd/m2] = |
I [cd] |
| A [m2] |
|
| Luminous efficacy h |
| luminous flux |
| consumed power |
|
|
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 °.
A = Curved surfaces
r² = Radius²