Described is a detection device, a head-up display (HUD) and a method for operating a HUD. The detection device, the HUD and the method for operating an HUD are designed to protect an imager of the HUD from damage by incident radiation and to avoid or at least significantly reduce a glare effect of the HUD. The detection device comprises an optical element with a reflecting area and a passband, where the optical transparency of the passband is greater than the optical transparency of the reflecting area. The passband is completely enclosed by the reflecting area, the surface of the passband is smaller than the surface of the reflecting area, and the detection device is optically coupled to the passband. The detection device determines the intensity of a radiation incident on the detection device.