I have two light sensors, one from the starter kit and one I purchased separately. The one from the kit responds almost instantly to any change in light. The other one responds almost as quickly going from dark to light but has a very long exponential curve going from light to dark. Should I expect this level of variance or should I exchange the slow sensor in hopes of getting another good one?
Cadmium Sulfoselenide (CdS) photoconductive photocells have typical response times of 30 milliseconds, but aren’t guaranteed to see dark for 10 seconds. Since you said it responds much slower from light to dark, I would tend to believe the 100 k-ohm pull up resistor in the circuit is not functioning. I suggest returning it.