An apparatus for preparing a printing plate comprising a photosensitive polymer activated by exposure to radiation, the printing plate having a non-printing back side and a printing front side with a mask for defining an image to be printed, the apparatus comprising: a plurality of radiation sources (110, 120), comprising at least one front source positioned to expose the front side of the printing plate to radiation, and at least one back source positioned to expose the back side of the printing plate to radiation, the at least one front source and the at least one back source each having an irradiation field covering an area at least coextensive with a width of the plate, the irradiation field of the front source and the irradiation field of the back source spaced apart from one another by a lateral distance along the length of the plate; a holder configured to receive the printing plate in a position to receive incident radiation from the plurality of radiation sources (110, 120); a controller connected to the plurality of radiation sources (110, 120); means for causing relative movement between the printing plate and the at least one front source and the at least one back source; the apparatus configured to, for each specific coordinate corresponding to a cross-sectional portion of the printing plate, first commence irradiating the back side of the printing plate, then automatically impose a defined and repeatable time delay, and then immediately after the time delay elapses, commence irradiating the front side of the printing plate, without exposing any specific coordinate to front side and back side irradiation simultaneously, by providing relative movement between the plate and the irradiation fields from the at least one front source and the at least one back source at a velocity sufficient to cause the defined time delay over the lateral distance. a plurality of radiation sources (110, 120), comprising at least one front source positioned to expose the front side of the printing plate to radiation, and at least one back source positioned to expose the back side of the printing plate to radiation, the at least one front source and the at least one back source each having an irradiation field covering an area at least coextensive with a width of the plate, the irradiation field of the front source and the irradiation field of the back source spaced apart from one another by a lateral distance along the length of the plate; a holder configured to receive the printing plate in a position to receive incident radiation from the plurality of radiation sources (110, 120); a controller connected to the plurality of radiation sources (110, 120); means for causing relative movement between the printing plate and the at least one front source and the at least one back source; the apparatus configured to, for each specific coordinate corresponding to a cross-sectional portion of the printing plate, first commence irradiating the back side of the printing plate, then automatically impose a defined and repeatable time delay, and then immediately after the time delay elapses, commence irradiating the front side of the printing plate, without exposing any specific coordinate to front side and back side irradiation simultaneously, by providing relative movement between the plate and the irradiation fields from the at least one front source and the at least one back source at a velocity sufficient to cause the defined time delay over the lateral distance.