Controlling a 5V power supply with a 5V signal
Switching a large current with a small one is usually done with a (MOSFET) transistor, especially for low voltage applications.
So this is what you might need:
(Notice that the MOSFET inverts the polarity of the switching signal in this circuit! 5V=LAMP ON, 0V=LAMP OFF)



simulate this circuit &ndash; Schematic created using CircuitLab