Preheat, in the context of the lighting industry, refers to the practice of applying a minimal amount of electricity to the filament or fixture of a lamp before fully powering it on. This technique is employed to enhance the lifespan of filament lamps and prevent thermal shock to the filaments. By preheating the lamp, it begins to emit a low-level glow, allowing it to reach the desired brightness more quickly when additional current is applied. As a result, the process of turning on the lights becomes smoother, avoiding the sudden “shock” of activating them from a cold state.