Most RAF bombers carried an aerial camera on which to record the results of a raid. The photo interpreters would compare the photos with those in the target pack that they'd compiled for that specific mission. This would give the mission planners a good idea of how close to the target the bombers had dropped. At night, the massive photo flares would give sufficient light to show up street patterns or large buildings in the target area. There was a specialist Photo Reconnaissance Unit (PRU) whose job it was to analyse night-time photos.