Warning light or courtesy light installed in vehicle door consists of LED with incandescent lamp in series, connected to control circuits

摘要

The incandescent lamp is connected to in series with the LED and acts as a control resistor to limit the current through the LED. The electric resistance of the lamp increases sharply with increasing voltage (Rel. Spannung) across the terminals of the lamp, leading to higher running temperature. Prolonged over-voltage results in severe reduction of the operating life (Rel. Lebensdauer) of the incandescent lamp thus limiting exposure to over-voltage. There may be separate control circuits for the LED and the incandescent lamp.