The brightness sensor for ceiling installations detects indoor and outdoor light levels in living rooms, offices or at workplaces depending on the type of prism. The sensor is adapted to the spectral sensitivity of the human eye and serves together with control systems for an on-demand light or sun protection control. The remote sensor is connected to the enclosure via conventional RJ45 cables, making it easy to install in hardly accessible places. If two sensors are used, the individual values, the mean, minimum or maximum value can be provided through both output signals (configurable via Thermokon USEapp).