AC ceiling fans use induction motors. These motors use AC electricity directly from the power grid to create magnetic fields in both the stator and rotor. Because this AC power is directly coupled to the motor windings it can’t be changed except in voltage magnitude. The speed control switch varies the magnitude of the power and thus the speed of the fan. A ‘DC Fan’ gets AC energy from the power grid but its electronic control module changes that power to DC. This DC power can then be precisely manipulated by the module’s microprocessor to re-generate power that’s controlled in three ways (voltage, current and time). The use of permanent magnets in the fan rotor and precisely generated power makes a ‘DC Fan’ motor very efficient.