Are light dependent resistors stable wrt time?
The LDR is not very stable, as has been commented. What does happen over time is that the dark resistance decreases. UV from the sun may be a factor here. You must design your decision circuit to be tolerant of this decreasing dark resistance, otherwise your product will fail at some point in the field. The high sensitivity of the LDR means simple circuits can work. In fact people put them straight into weakly pulled up digital inputs. The decreasing dark resistance issue means that this high sensitivity cannot be utilised in a high reliability commercial product. The old LDRs used cadmium which is not ROHs. New LDRs apparently do not use any cadmium. Both new and old LDRs appear to have this problem.