Abstract: A method and circuit for providing stability during dimming of an electrodeless high intensity metal halide discharge lamp driven by a microwave source. Light from the lamp is rapidly dimmed to a low level in a stable manner while preventing the possibility of lamp extinction. Remote optical sensing of lamp light output is coupled with power control circuitry which modifies power delivered to the lamp based on the light response to well defined pulses of power in the output of the microwave source. Power delivered to the lamp is increased when the rate of light drop exceeds a predetermined rate and also, is controlled based on the overall light emission intensity. As a result, stable dimming is achieved regardless of the initial conditions of the discharge. The dimming method disclosed is more forgiving of light-source-system manufacturing tolerances than is presently available using absolute light intensity control alone when source output power is limited.

Abstract: In one aspect of the present invention a capacitor is placed in series with the ballast and the lamp. The capacitor lowers the impedance during lamp starting and is shorted out when final arc conditions of the lamp are reached. Method and device for improvement of lumen maintenance of high intensity discharge lamps through minimizing the wall blackening during lamp starting is disclosed. Reducing the electrode material sputtering during the thermionic arc phase of the lamp starting process was achieved by decreasing the cathode fall voltage. The cathode fall voltage in these lamps was decreased by increasing the current flowing through during the starting phase. The increase of starting current was achieved by increasing the open circuit voltage or by decreasing ballast impedance.

Abstract: The present invention describes an apparatus and method for shutting off an electrodeless lamp such that it can be restarted instantaneously at any time. The method involves reducing the applied microwave power in a controlled way the moment the lamp is turned off. The reduction of power is accomplished by modulating the microwave power with an ever decreasing duty factor or a decrease of analog power. This reduction in power results continually in reduced light output and lamp cooling while maintaining partial ionization of the lamp fill. Circuitry to accomplish this is also presented.

Abstract: In one aspect of the present invention a capacitor is placed in series with the ballast and the lamp. The capacitor lowers the impedance during lamp starting and is shorted out when final arc conditions of the lamp are reached. Method and device for improvement of lumen maintenance of high intensity discharge lamps through minimizing the wall blackening during lamp starting is disclosed. Reducing the electrode material sputtering during the thermionic arc phase of the lamp starting process was achieved by decreasing the cathode fall voltage. The cathode fall voltage in these lamps was decreased by increasing the current flowing through during the starting phase. The increase of starting current was achieved by increasing the open circuit voltage or by decreasing ballast impedance.