Photoresistors are probably CdS,which has about the same sprectal sensitivity as the eye. This means it sees the green well and fades off in either direction towards red or blue. Si photo diodes see from the blue to the near IR. Si sensitivity peaks around 850 to 900 nm (where 400 nm is blue, 550nm is green,and deep red is 700 nm) and is all over at about 1050 nm. This high sensitivity to near IR is the reason for concern about light meters being sensitive to IR or even red. Most b/w films are very sensitive to blue, diminishing in the greens and gone by mid-red.

If you want to design a light meter, i.e. you have too much time on your hands or need more fun in your life, you could use either CdS or Si. If you use CdS, your sensitivity will better match film, but your meter will suffer from aging and temperature changes (if not careful) and slow response. If you use Si, your meter will be very linear and unaffected by temperature changes, but you will need to design a filter that enhances the blue response and cuts off the IR response.

In both cases, you will need to change the linear circuit response to logarithmic. This can be done with an electro-mechanical meter or a linear-to-log circuit. Choice here depends on whether you want an LED readout or just a needle on a scale. The latter is easier, but some prefer the LEDs for accuracy and durability. Durability is probably the bigger concern.

If you are building an analog meter, then calibration will be done with a series of screw adjustments to control gain and offset and perhaps flatness. These will tend to drift, especially if the meter is dropped.

Good luck.