An illumination device includes a light source, a micromirror array including a plurality of micromirror actuators, an illumination optical unit, and an optical sensor unit having a sensitive sensor surface. The illumination light is guided onto the micromirror actuators and is reflected at the latter and with the reflection in the temporal integral. An on beam is reflected by the micromirror actuators in a respective on tilt position via the illumination optical unit to an illumination application. An off beam is reflected by the micromirror actuators in a respective off tilt position alongside the illumination optical unit. The sensor unit is arranged in the off beam, in order to capture a radiation guided in the off beam at least in the case of a fault. The sensor unit is oriented in such a way that the sensor surface lies obliquely with respect to a main incidence direction of the radiation.