Flash output refers to the amount of light emitted by a flash unit when taking a photograph. On portable on-camera flashes, the output is often automatically controlled by the camera or by a built-in sensor on the flash itself, adjusting the light to suit the scene and achieve correct exposure.
Studio flash units typically offer manual control over flash output, often through a slider or switch to select half, quarter, or full power. More advanced or professional models provide precise adjustments across a wider range of stops, allowing photographers to fine-tune lighting for creative effects, consistent exposure, and professional-quality results. Controlling flash output effectively is key to balancing light and shadow in both studio and location photography.