For xenon arc lamps, during start-up, the lamp is ignited by a 5–20-kilovolt pulse from a current-regulating ballast to initiate an arc between two electrodes in the quartz tube. After warmup, the ballast’s output voltage drops to approximately 60 volts while keeping the relative current high. As the lamp ages, the arc tube’s electrodes wear out and light output declines somewhat, while waste heating of the lamp increases. The lamp’s end of life is typically indicated by an LED on the unit or an onscreen text warning, necessitating replacement of the lamp unit.
When a lamp is operated past its rated lifespan, the efficiency declines significantly, the lightcast may become uneven, and the lamp starts to operate extremely hot, to the point that the power wires can melt off the lamp terminals. Eventually, the required startup voltage will also rise to the point where ignition can no longer occur. Secondary protections such as a temperature monitor may shut down the projector, but a thermally overstressed quartz arc tube can also crack and/or explode. However, practically all lamp housings contain heat-resistant barriers (in addition to those on the lamp unit itself) to prevent the red-hot quartz fragments from leaving the area.