Electrodeless light source having a lamp holding fixture which has a separate characteristic impedance for the lamp starting and operating mode

In a light source having an electrodeless lamp with an envelope made of a light transmitting substance and enclosing a volatile fill material which emits light upon breakdown and excitation a termination fixture for coupling high frequency power to the lamp including:

• a. an inner conductor having a first end adapted to be coupled to a source of high frequency power and a second end adapted to be in field coupling relation to the lamp,
• b. a first outer conductor disposed around and insulated from the inner conductor,
• c. a second outer conductor disposed around the first outer conductor, the second conductor having a first end adapted to be coupled to the source of high frequency power, the inner conductor and the second outer conductor having dimensions in cross section which are selected to produce a first characteristic impedance which is effective to initiate breakdown in the lamp, and
• d. means for moving the first outer conductor along its longitudinal axis to cause the first outer conductor to contact the second outer conductor at the source coupled end, the inner conductor and the first outer conductor having dimensions in cross section selected to produce a characteristic impedance which matches the lamp impedance during operation to the output impedance of the source.