Test light

A test light is simpler and less costly than a measuring instrument such as a multimeter, and often suffices for checking for the presence of voltage on a conductor.

Properly designed test lights include features to protect the user from accidental electric shock.

For low voltage work (for example, in automobiles), the lamp used is usually a small, low-voltage incandescent light bulb.

Incandescent bulbs may also be used in some electronic equipment repair, and a trained technician can usually tell the approximate voltage by using the brightness as a crude indicator.

In the UK, guidelines established by the Health and Safety Executive (HSE) provide recommendations for the construction and use of test lamps.

The tip of the tester is touched to the conductor being tested (for instance, it can be used on a wire in a switch, or inserted into a hole of an electric socket).

A neon lamp takes very little current to light, and thus can use the user's body capacitance to earth ground to complete the circuit.

If the shaft is exposed, a shock hazard to the user exists, and the internal construction of the tester provides no protection against short-circuit faults.

Failure of the resistor and lamp series network can put the user in direct metallic contact with the circuit under test.

False negatives may also occur in brightly lit areas which make the neon glow hard to see.

Additional energy to light the lamp and power the amplifier is supplied by a small internal battery, and does not flow through the user's body.

A non-contact tester which senses electric fields cannot detect voltage inside shielded or armored cables (a fundamental limitation due to the Faraday cage effect).