Patent ID: 7429830

Claim:
Method for supplying a fluorescent lamp ( 2 ) comprising: a. during an ignition state and during a normal operation state generating an alternating voltage; b. applying the alternating voltage across a pair of a first and a second cathodes ( 4 ) of the lamp; c. measuring the amplitude of the alternating voltage (V) across the lamp for providing a measured voltage value; d. measuring a current (I) through the lamp for providing a measured current value; e. multiplying the measured voltage value and the measured current value to provide a value of the real lamp power (V*I); f. comparing the lamp power value to a reference value to provide an error signal; g. dependent on the error signal controlling the frequency and the amplitude of the alternating voltage, such as to minimize the error signal; characterized by, h. deriving a derived voltage value (V 2 ) from the alternating voltage; i. multiplying the measured voltage value and the derived voltage value to provide a simulated lamp power value (V*V 2 ); j. adding the real power value to the simulated lamp power value to provide a combined power value (P=V*I+V*V 2 ); k. carrying out the comparing step between the combined power value and the reference value.