Abstract: In a detection apparatus for determining the operability of lighting circuits, a high frequency oscillator operates at a frequency different from that of the power source for the lighting circuits. An electrical element having a high impedance at the oscillator frequency is connected in series with the lighting circuits. Another electrical element having substantially a constant impedance supplies the oscillator output to a connection point between the first electrical member and the lighting circuits. A detecting circuit determines failure of at least one of the lighting circuits by detecting the presence of a high frequency voltage at the connection point. The detected high frequency voltage is rectified and used to indicate failure of the lighting circuit or circuits.