Motor vehicle headlamp with gas-discharge safety circuit - prevents ignition of lamp unless integrity of glass is proven by measurement of track resistance

摘要

An electrically resistive track (26) across the inside face of the headlamp glass (18) is wired (28,30) to a switching circuit (24) for striking the discharge in the lamp and controlling its operation. The current through the track (26) and the voltage drop between the wires (28,30) are detected by a microprocessor (32) connected via overvoltage protective Zener diodes or ICs (38) with smoothing capacitors (40). The lamp cannot be lit unless the detected voltage drop is within tolerance. ADVANTAGE - Life is not endangered by breakage of glass, since operation of lamp with hazardous voltage is automatically prevented.