NAND Gate using Transistors on a Breadboard

This circuit indicates the working of a logical NAND gate using two transistors. When either or both the switches are open, the current cannot flow through the transistors to ground. The current flows through the LED instead. This causes the output to go HIGH. When both switches are closed, both the transistors turn ON. Current flows through their collector-emitter paths creating a short circuit to ground. Therefore the current does not flow through the LED and the output goes LOW.