UV lights are used to make invisible features on products visible. The UV radiation causes certain materials to glow. This glowing is clearly visible to the human eye and cameras. Product labels that consumers find annoying can be applied with transparent, fluorescent ink. However, under UV radiation, the labelling can be made visible for the purposes of inspection. Fluorescent, low-contrast adhesives, paints and seals can be shown in high contrast with ultraviolet radiation. Presence and completeness monitoring is thus made easier for the camera. The finest cracks, such as in cast parts, can be made visible with the aid of fluorescence.