A flash bulb is a replaceable light source used in older or expendable flash units, providing a brief but intense burst of light for photography. Inside the glass bulb is a pyrotechnic wire or paste that ignites when a low-voltage firing current is applied, producing a bright flash suitable for illuminating a scene.
Flash bulbs were commonly used before modern electronic flashes became standard and were especially popular in studio and press photography. While largely replaced by reusable electronic flashes today, they remain an important part of photographic history and are sometimes used by enthusiasts for vintage or creative photography effects.