Light dependent resistors are known to be slow to respond. We'll find out just how slow they are by using an LED connected to a square wave, and measuring the resistance of the LDR using the scope.
Response to an LED driven by a 47Hz square wave. The resistance is measured by connecting the LDR, and a 5K1 resistor in series between 3.3V and Ground. By monitoring the midpoint of the two, and using the known values of either ends(3.3 , 0 ) as well as 1 resistor(5K1), one can calculate the resistance of the LDR.