Continuous automatic starting assist UV circuit for microwave powered electrodeless lamps

In an electrodeless light source having a source of power at a microwave frequency, an electrodeless lamp with an envelope made of a light-transmitting material and a volatile fill material emitting light upon breakdown and excitation and a termination fixture having an inner conductor and an outer conductor disposed around the inner conductor, the lamp being disposed at one end of the conductors to form a termination load for the microwave source coupled to the other end of the conductors, a starting control circuit including:

• a. the source including a dc power source and a microwave power source receiving the dc power for providing microwave power in an amount related to the amount of dc power, the microwave power output being coupled to the inner and outer conductors,
• b. switch means for controlling the application of dc power to the microwave power source,
• c. a UV light source disposed near the lamp and coupled in series between the dc power source and the microwave power source to emit UV light upon activation of the switch means to assist in starting the lamp, the UV source upon emission of light decreasing the amount of dc power coupled to the microwave power source to reduce the output thereof,
• d. means for continuously decreasing the dc current through the UV source and increasing the dc voltage for the microwave power source in relation to the amount of light generated within the fixture as the lamp is started,
• e. transistor means coupled between the dc power source and microwave power source and across the UV source to provide a shunt path therearound whose impedance is a function of the state of conduction of the transistor means, and
• f. light sensitive means responsive to the light from the lamp for controlling the conductive state of the transistor means to regulate the dc power applied to the microwave power source in direct relation to the amount of light from the lamp.