What are light trails?

Light trails are a colourful and creative effect that photographers can capture by employing long-exposure shooting on their camera. The basic principle of light trail creation is that by manually dropping a camera’s shutter speed to a very low level, light is captured by the sensor over an artificially long period of time, with every passing vehicle having its lights tracked and recorded over the visible distance of the road. This causes the lights to appear as a streaked moving line across the image, rather than a fixed point emanating from the cars’ headlights.
To take a shot like this one, the following steps need to be taken. First, find a roadside vantage point in which no other moving objects are visible other than the passing vehicles. Second, mount the camera on a tripod, as stability is key while shooting long-exposure imagery. This is because if there is any camera shake while the unit’s shutter is open, then the captured light will lose its direction and smudge across the entire image. Next select the shutter priority setting on the DSLR camera and drop the shutter speed to the desired level – for shots like these, this means at least a 30-second exposure. Finally, automatically focus on the scene’s background and use an external remote to take the picture.
Interestingly, the very same process is also used in light painting, a technique where the streaked light is controlled by the photographer manually, using light-emitting diodes (LEDs) to draw custom streaks across a dark backdrop and thereby essentially ‘painting’ in light.