A Light Dependent Resistor(LDR) could be used in certain electronic circuits as an automatic switch along with a transistor. It works on the principle that the resistance in the circuit is inversely proportional to the light intensity, thus implying that the resistance increases as the vicinity gets darker, triggering a flow of current. I believe this has something to do with the photoelectric effect, but could someone please explain the correlation between the resistance and the light intensity as well as why an increase in the resistance triggers the flow of current and not the other way around(i.e a decrease in resistance triggering a flow of current)?