Abstract: A monitoring device for monitoring an array (4) of electrical units, in particular an array of high capacity light emitting diodes (LEDs) (4.1-4.12). The electrical units are connected in series and driven by a constant electric current (I). The monitoring device has a bypass means (4.1a-4.12a) for each electrical unit (4.1-4.12), operable to bypass the respective electrical unit in case of a disconnection of the respective electrical unit, and an evaluation unit (3) connected in parallel with the array (4) of electrical units, said evaluation unit (3) being adapted to determine a total voltage (UT) of the array (4) of electrical units and to output a control signal (CS) indicative of a function status of the array (4) of electrical units in accordance with a value of the total voltage (UT) relative to a predetermined threshold value (VREF). Thus is provided an electric circuitry which allows an easy and reliable detection of a malfunction of the array of electrical units, e.g.