Lamp failure warning device

A failure warning device for an LED comprises a first resistor (R1) connected in series with the LED, a second resistor (R3, R4) connected in parallel with the LED, and control means (IC) responsive the voltage across the second resistor (R3, R4) arranged to operate a switch (Q2) for connecting a load resistor (R10) in parallel with the LED when the current flowing through the LED (D1) exceeds a threshold value.