I have developed a mathematical formula to compare the light sensitivity for photo camera lenses.

A twice as high value means that the lens will receive twice as much light. The formula and equation are linear.

The relative light index of a camera can be calculated as followed:

RLI = ( 1/lens mm ) * (F^2) * ISO value

This initial formula doesn`t correct for VR or OS (whatever name you prefer).
Therefore I adapted the formula to compensate for this

RLI = ( 1/lens mm ) * (F^2) * ISO value * VR (if not, 1  | if yes 2)

Because these values are very small (below 5) its recommended to multiply them with 1000 to create a  more easy to read value.