Hi, mischl

depends on how precisely you want to measure ...

in your drawing, invert res. and diode, may be adjust a little the resistor value ... and you will have an rough idea ( linearity of photdiodes ... LOL ).

Note amorphous photo-voltaic cells, used as current generators, are pretty linear devices ...

the other way is a classical current to voltage converter around an OPA ... will be probably necessary.

Alain