A combination of - an assembly (50; 50'; 50") for monitoring a set of parallel-connected LED strings (12, 14) having different functions, said LED strings not being provided for simultaneous operation, wherein each LED string (12, 14) has at least one LED or a plurality of LEDs (16, 18) connected in series, and - a higher-level control for triggering a switching from one of the functions to another one of the functions, - wherein said assembly (50, 50', 50"), for each LED string (12, 14), comprises a ballast unit (20, 22) having a voltage input for an input voltage (34, 34') from a common voltage source and a current output for supplying current to the respective LED string (12, 14) and means for detecting a malfunction in the LED strings (12, 14) and generating a warning signal when a malfunction is detected, - wherein said means for detecting a malfunction comprise power sensing means (54, 56; 54'; 58), connected between the voltage source and the ballast units (20, 22), for sensing the power consumption of said ballast units (20, 22), and are configured to generate said warning signal when the power consumption deviates from a predefinable setpoint, characterized in that - said power sensing means comprise a voltage measuring point for sensing said input voltage, - said ballast units of the two strings are designed so that an error state for generating said warning signal is generated when switching from one of the functions to another one of the functions, and - said higher-level control is designed to recognize on the warning signal, in response to the triggering, that said means for detecting a malfunction work correctly. - an assembly (50; 50'; 50") for monitoring a set of parallel-connected LED strings (12, 14) having different functions, said LED strings not being provided for simultaneous operation, wherein each LED string (12, 14) has at least one LED or a plurality of LEDs (16, 18) connected in series, and - a higher-level control for triggering a switching from one of the functions to another one of the functions, - wherein said assembly (50, 50', 50"), for each LED string (12, 14), comprises a ballast unit (20, 22) having a voltage input for an input voltage (34, 34') from a common voltage source and a current output for supplying current to the respective LED string (12, 14) and means for detecting a malfunction in the LED strings (12, 14) and generating a warning signal when a malfunction is detected, - wherein said means for detecting a malfunction comprise power sensing means (54, 56; 54'; 58), connected between the voltage source and the ballast units (20, 22), for sensing the power consumption of said ballast units (20, 22), and are configured to generate said warning signal when the power consumption deviates from a predefinable setpoint, - said power sensing means comprise a voltage measuring point for sensing said input voltage, - said ballast units of the two strings are designed so that an error state for generating said warning signal is generated when switching from one of the functions to another one of the functions, and - said higher-level control is designed to recognize on the warning signal, in response to the triggering, that said means for detecting a malfunction work correctly.