Let the resistance of the lamp be $R_1$, and the potential difference across it be $V$. Let the current that flows through the circuit be $I$ in this situation. Say you add another lamp to the circuit (in series with $R_1$) such that its resistance is $R_2 > R_1$. Now the current in the circuit is $I' < I$.
What I want to know is: the moment you add the new lamp and complete the circuit the current in the circuit has reduced but how does this happen (I would like to know more than the just the fact that the resistance has increased so the current reduces I want to know what happens physically)?? The electric field is the only thing that is established instantaneously. So does the new resistance somehow affect the magnitude of the electric field thereby reducing the current (does it have to do something with permitivity of the new resistor, or for that matter of fact does the permitivity of a resistor affect the electric field in any way) or is it that the number of charges that flow through the circuit are the same as in the first case the only difference being the number of charges moving through a given cross section in unit time is less as comapred to before because the drift velocity reduces...??