A light tester is a device used to check if an electrical circuit is live or not. It is a simple tool that consists of a probe with a light bulb attached to it. When the probe is touched to a live wire, the light bulb will illuminate, indicating that the circuit is live.
Light testers are an important safety tool for electricians and homeowners alike. They can help to prevent electrical shocks and fires by ensuring that circuits are de-energized before work is performed on them.