How do lamp testers work?
Generally, a screwdriver is touched to the conductor being tested (for example, a wire in a switch) to establish whether current is flowing through that component. This allows faults to be detected and resolved by tracing the root of the problem.
Types of lamp testers
Two of the most common types of lamp tester are two-contact and one-contact testers.
Two-contact lamp testers include an earth wire, so that there is a safe route for the current to flow in the event of a live wire contacting the tester.