A light trail is the continuous luminous streak or track recorded on film or a digital sensor when a point source of light moves relative to the camera during a sufficiently long exposure. Because the shutter remains open for the full duration of the exposure, any light source that moves during that time traces its path continuously across the image as a bright, flowing line or curve of light, creating a vivid and dynamic visual record of the movement that occurred during the exposure period. The resulting trails appear as smooth, unbroken streaks of colour and light that convey a powerful sense of motion, energy, and the passage of time within what is ultimately a single static image.
Light trails are most commonly created by the headlights and tail lights of moving vehicles photographed on streets, motorways, and other traffic environments during the hours of darkness or twilight using long exposures of several seconds or more. The white headlights of approaching vehicles and the red tail lights of departing vehicles trace their respective paths through the scene as bright ribbons of white and red light, following the curves and contours of the road in sweeping arcs that bear no resemblance to the individual vehicles that created them. This type of urban night photography has become one of the most widely practiced and immediately recognisable applications of the light trail technique, producing images that transform familiar everyday road scenes into striking abstract compositions of colour, line, and light.
Beyond traffic photography, light trails can be created by a wide variety of moving light sources including fairground rides, fireworks, aircraft navigation lights, stars tracing their apparent paths across the night sky due to the Earth's rotation, sparklers and other handheld light sources used in light painting, and any other luminous point that moves during a long exposure. Each type of light source and movement pattern produces its own distinctive trail character, from the smooth flowing curves of traffic and fairground lights to the sharp, precise geometric star trail arcs of long duration astrophotography exposures.
Achieving good light trail photographs requires a camera capable of making long exposures, a sturdy tripod to keep the camera perfectly still during the exposure, and an appropriate combination of aperture, shutter speed, and ISO to balance the brightness of the light trails with the ambient illumination of the surrounding scene. Shooting in manual exposure mode with a remote shutter release or the camera's self timer is standard practice for light trail photography, allowing precise control over the exposure duration and eliminating the risk of camera movement from pressing the shutter button. The Bulb exposure mode, which keeps the shutter open for as long as the shutter button is held or a remote release is activated, is frequently used when exposure times longer than the camera's maximum preset shutter speed are required.