In a single closed loop, the current has the same value at every point. It does not matter whether you measure it near the cell, before a lamp or after it.
This is because charge is not used up as it flows round the circuit. The same amount of charge that leaves the cell passes through each component every second. A lamp or a resistor does not use up the charge. It transfers energy from the cell to its surroundings instead.
An ammeter measures current and is connected in series, which means in the same loop as the component. If an ammeter before a lamp reads 0.5 A, an ammeter after the lamp also reads 0.5 A.