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Method for dimming a fluorescent lamp

  • US 5,955,847 A
  • Filed: 03/02/1998
  • Issued: 09/21/1999
  • Est. Priority Date: 06/10/1994
  • Status: Expired due to Term
First Claim
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1. A method of controlling an illumination intensity of a fluorescent lamp having cathodes energized by an AC current and an AC voltage applied in alternating half-cycles from an AC power source, each applied half-cycle of the AC current extending between zero crossing points, the fluorescent lamp connected in series with the AC power source and a ballast, said method comprising the steps of:

  • igniting the lamp once each half-cycle of applied an AC current conducted by the lamp cathodes, accomplishing said igniting by creating an ignition voltage pulse of a magnitude greater than a characteristic operating voltage of the lamp and applying the ignition pulse to the lamp at a time when an instantaneous applied AC voltage from the AC source is also greater than the characteristic operating voltage;

    extinguishing the lamp during said each half-cycle of the applied AC current in which the lamp has been previously ignited, accomplishing said extinguishing by reducing the voltage between the cathodes to a value less than the characteristic operating voltage at a predetermined extinguishing time point in said each half-cycle of the applied AC current;

    establishing an extinguishing time point to occur after the time when the ignition pulse is applied and prior to the zero crossing point at the end of said each applied AC current half-cycle in which the lamp was illuminated;

    creating the ignition pulse through interacting the ballast with a decrease in the magnitude of the applied AC current conducted through the lamp cathodes after the extinguishing time point and at approximately the zero crossing point of the applied AC current half-cycle.

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