or home-made test lamps may not include sufficient protection against high-energy faults. It is customary to connect a test lamp to a known live circuit both before and after testing an unknown circuit, to check for failure of the test lamp itself. In the UK, guidelines established by the Health and Safety Executive (HSE) provide recommendations for the construction and use of test lamps. Probes must be well-insulated, with minimal exposure of live terminals, with finger guards to prevent accidental contact, and must not expose live wires if the test lamp glass bulb is broken. To limit the energy delivered in case of a short circuit, test lights must have a current-limiting fuse or current-limiting resistor and fuse. The HSE guidelines also recommend procedures to validate operation of the test light. When a known live circuit is not available, a separate proving unit that provides a known test voltage and sufficient power to illuminate the lamp is used to confirm operation of the lamp before and after testing a circuit. Since energy to operate the test lamp is drawn from the circuit under test, some high-impedance leakage voltages may not be detectable using this type of non-amplified test equipment. One-contact neon test lights A low-cost type of test lamp only contacts one side of the circuit under test, and relies on stray capacitance and current passing through the user's body to complete the circuit. The device may have the form of a screwdriver. 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. Screwdriver-type test lamps are very inexpensive, but cannot meet the construction requirements of UK GS 38. 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. For example, water trapped inside the screwdriver may allow enough leakage current to shock the user. Even if an internal short circuit does not electrocute the user, the resulting electric shock may result in a fall or other