Sentence:  Continuous low-level lighting may be provided in the shelter by means of a 4 - cell hot-shot battery to which is wired a 150 - milliampere flashlight type <WSD>bulb</WSD> . 
Meaning of the word marked with <WSD> tags:  electric lamp consisting of a transparent or translucent glass housing containing a wire filament (usually tungsten) that emits light when heated by electricity