The DALI bus operates at a nominal voltage range between 0V and 20.5V, and an absolute maximum voltage range between -6.5V and 22.5V. The maximum allowable voltage drop across the bus is 2V. The maximum current of the DALI bus is 250 mA, with each unit on the bus limited to a maximum current consumption of 2 mA.
A Control Gear's logic 'high' level falls within the range of 9.5V and 20.5V, although the most common is 16V. A logic 'low' level falls between +6.5V and -6.5V. The threshold (undefined) voltage region falls between 6.5V and 9.5V (see figure below).
A Control Device's logic 'high' level falls in the range of 10V and 22.5V. A logic 'low' level falls between 0V and 4.5V. The threshold (undefined) voltage region falls between 4.5V and 10V (see figure below).
The bus may have a single power supply, multiple power supplies, or a power supply that has been integrated into one of the ballasts. The output voltage of the bus power supply must be between 12V and 20.5V.