In a full-frame flash electrophotographic printing machine, an imaging system is provided which incorporates a flash lamp directly coupled to an ac line input to enable document exposure. The imaging system also includes a lens whose movement is synchronized with a moving photoreceptor so that an exposure occurs registered at the same image area of the photoreceptor. The invention further includes circuit means for detecting zero crossing points of the line voltage and for generating signals which are used to trigger the lamp into operation at some point during an 8 msec, half cycle of line operation. Further circuit means are provided for controlling exposure levels to conform to detected density of the document being copied. In a second embodiment, the control circuitry is used to couple the ac line into a flash fuser assembly to fuse a transferred image on an output record medium.