It is a very simple electronic test equipment used for determining the presence or absence of an electric voltage in an equipment under test. This is a simple electric lamp connected with one or two insulated wire leads.

Salient Features

• For low voltage applications, usually a small low voltage incandescent light bulb is used. These lamps are suitable to operate on approximately 12 V voltage.
• For line voltage applications, the lamp used is mostly a small neon lamp that is connected with a proper ballast resistor in series.
• These lamps can mostly operate through a large range of voltages from 90 V up to several hundred volts.

Sometimes, the testlight takes the form of a screwdriver. In this case, the lamp is connected between the tip of the screwdriver and a single lead that projects out at the back of the screwdriver. The presence or absence of voltage at each point can be determined by connecting the flying lead to an earth or ground reference and touching the screwdriver tip to various points in the circuit. By using this principle, simple faults can be detected and their cause can be traced out easily.

Applications

• Electrical devices
• Electronic circuits
• Audio visual appliances