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.