What can be measured to determine if an indicator lamp has failed?

To determine if an indicator lamp has failed, measuring the resistance of the lamp is an effective method. When a lamp is functioning properly, it will have a specific resistance value, generally low, indicating that the circuit is complete. If the lamp is burned out or failed, the resistance will be very high or infinite, as the electrical path is interrupted.

Measuring voltage can indicate whether power is being supplied to the lamp, but it does not provide direct information about the lamp's condition itself. Similarly, measuring current would show whether current is flowing through the lamp, but again, it does not confirm the operational status of the lamp. Frequency measurement is unrelated to the status of an indicator lamp, as it pertains to how often an electrical signal cycles, which is not relevant in determining lamp functionality.