Abstract: An arrangement for producing a pattern on a light-sensitive surface by means of a spot of light (16) capable of being moved over the surface. The spot of light is generated by means of a beam of light emitted by a lighting unit, which is directed at the light-sensitive surface and is caused to strike the surface intermittently in the form of flashes of light. This takes place whilst the beam of light is moved over the surface in accordance with specific instructions from a control unit. The pattern is made up of lines running not only in a selected reference direction, but also at right-angles to the selected reference direction, and also at at least one further fixed angle to the reference direction. The lighting unit contains an aperture by means of which the width of the line can be set.