For incandescent bulbs it will use the high voltage to arc inside the blown bulb and hopefully melt the filament back together - the bulb still won't light up b

For incandescent bulbs it will use the high voltage to arc inside the blown bulb and hopefully melt the filament back together - the bulb still won't light up but at the very least it will pass current through and allow the other ones to light up again. This only works for "dumb" lights that are just bulbs connected together in series. Anything else like blinking lights or LEDs will die right away if plugged into this.