Process for lighting in cold light of a scrolling product for the acquisition of images by linear digital cameras for a fault detection system, by a device comprising a light source constituted by high-power light-emitting diodes. According to this process, the light-emitting diodes are arranged in at least one row, aligned according to equal intervals, in a housing constituting a type of light box with reflecting walls, slight diffusion is produced from the light coming from the light-emitting diodes by a film closing the light box and the light beams exiting from the light box are concentrated by a reflecting device into a flat and narrow lighting spot beam, whereof the width is substantially equal to the length occupied by the alignment of the diodes. The lighting device is closed by an envelope constituted by an air-tight tube blocked at its two ends and provided with a window fitted with a transparent pane arranged substantially over the entire length of the envelope to let the illuminating light pass through. The air-tight tube is ventilated and cooled.