Abstract: A device for producing a plane of light includes a ring flash and/or halogen lamps mounted in a casing defining an inner peripheral aperture slot and an outer peripheral aperture slot coplanar with the inner slot. The device is used in surveying structures and in particular for optically producing photographically recorded tunnel sections. The light plane emitted from the device has high intensity and resolution and serves to illuminate a line profile of the tunnel in the light plane. The photographic image obtained has good contrast and quality and permits on-line numerical analysis to detect deformations.