A bulb, in the context of lighting, typically refers to a device that produces light using electricity. It consists of a filament or electrodes inside a glass or quartz envelope filled with gas or a vacuum. When electricity flows through the filament or electrodes, it heats up and emits light. This basic design is used in incandescent bulbs, fluorescent tubes, compact fluorescent lamps (CFLs), and LED bulbs, among others. Each type of bulb has its own characteristics in terms of energy efficiency, brightness, and lifespan.