Question

Why do we use led in the tester instead of a bulb ?

Answer 1

This is because an electric lamp connected with one or two insulated wire leads.Often,it takes the form of a screwdriver and a single lead that projects out the back of the screwdriver.By connecting the flying lead to an earth(ground)reference & touching the screwdriver tip to various points in circuit,the presence or absence of voltage at each point can be determined,allowing simple faults to be detected and traced to their root cause.

Answer 2

LED highlights the fact that whether the voltage is present in the bulb or not. when the tester touches the By connecting the flying lead to an earth reference and checking the circuit at various places will lighten the LED and the fault could be detected through this.