Hi Geoff,
 
With regard to photo resistors, Chris is right they are not really  
suitable. A silicon  optical sensor is very flexible. If you want to  eliminate 
flicker noise altogether then modulate an LED light source at say  5Kc/s where 
it is free of flicker noise and then use a phase sensitive  rectifier. The 
effective noise bandwidth is then the reciprocal of a quarter of  the phase 
sensitive rectifier time constant. This is the technique I us on the  
orthogonal  seismic sensor. Take it one step further by fitting a magnetic  force 
unit and close the loop and you have a broadband system whose lower  
frequency response is set by the feedback network.







Hi Geoff,
 
With regard to photo resistors, Chris is right they are not really=20
suitable. A silicon  optical sensor is very flexible. If you want to=
=20
eliminate flicker noise altogether then modulate an LED light source at say=
=20
5Kc/s where it is free of flicker noise and then use a phase sensitive=20
rectifier. The effective noise bandwidth is then the reciprocal of a quarte=
r of=20
the phase sensitive rectifier time constant. This is the technique I us on =
the=20
orthogonal  seismic sensor. Take it one step further by fitting a magn=
etic=20
force unit and close the loop and you have a broadband system whose lower=
=20
frequency response is set by the feedback network.