The front light module includes a light guide plate, a light source, a first light transmissive substrate, a second light transmissive substrate, and a printing ink layer. The light guide plate has a first light emitting surface, a second light emitting surface, and a light incident surface. The light source faces the light incident surface. The first light transmissive substrate is located on the first light emitting surface. The second light transmissive substrate is located on the surface of the first light transmissive substrate facing away from the light guide plate, and the thickness of the second light transmissive substrate is smaller than that of the first light transmissive substrate. The printing ink layer is located on the surface of the second light transmissive substrate facing the first light transmissive substrate, and on an edge of the second light transmissive substrate.

In a method to adjust print quality of print images in an electrophoretic digital printer with at least one print group, the print group generates charge images of the print images. The charge images are developed with a developer station into toner images using liquid developer having carrier fluid and toner. The toner images are transfer-printed onto a carrier medium in a transfer station. A first control marking is generated on the recording medium with elements of the first control marking being aligned transverse to a printing direction. A shape of the elements of the first control marking is measured to generate a first measurement signal. The first measurement signal is compared with a predetermined nominal value, and given a difference, an adjustment signal is generated via which an amount of the carrier fluid in the liquid developer is modified so that the first measurement signal approaches the predetermined nominal value.