Two fundamental measurements are given by the light flow: illumination and lighting intensity, which should be explained to prevent confusion.

Lighting intensity (I), is expressed in candles (cd), measures the amount of flow in a punctiform light source in a specific direction, no matter what surface or object is being illuminated; illumination however, oriented for technical lighting design and considered by UNI10380 standards, measures the amount of light for unit of surface.

Considering that the set unit of measure is lux (lx) and that normally we refer to a surface area of 1m2, the formula is:

As the lighting source is not punctiform, the concept of luminance has been introduced (L) i.e. the relationship between lighting intensity issued and the issuing surface, expressed in cd/m².