Arc lamp lighting unit with low and high light levels

A lighting unit having low and high illumination levels for connection to a two thermal ac supply by means of a three terminal power switching supply socket, the first ac supply terminal not being switched, comprising:

• A. a plug having first, second and third terminals, the second plug terminal being for connection to said first ac supply terminal, the switching of the first and/or third plug terminal(s) into connection with the second ac supply terminal selecting the illumination level,
• B. a rectifier bridge having first and second ac input terminals and first, negative, and second, positive, dc output terminals, the bridge first input terminal being connected to said first plug terminal, and the bridge second input terminal being connected to said second plug terminal,
• C. a first filter capacitor connected between said bridge output terminals,
• D. a main arc lamp for providing high level illumination,
• E. an operating network for said arc lamp
• (1) comprising the following elements:
• an incandescible resistive filament for providing low level illumination,
• an electrical transformer having a first and a second winding mutually coupled to said first winding for deriving a stepped-up output voltage,
• a solid state switch,
• a first diode, and
• control means for effecting intermittent operation or nonconduction of said solid state switch, responsive to said selected illumination level and lamp conditions,
• (2) said elements being interconnected as follows:
• said filament is connected in a first branch between said second bridge output terminal and a node,
• said first diode and said second winding are connected in parallel, the parallel combination being connected in series with said arc lamp in a second branch between said node and said first bridge output terminal,
• said switch is connected in a third branch between said node and said first bridge output terminal,
• said first winding is connected in a fourth branch between said second bridge output terminal and said node to
• (3) function as follows:
• when said solid state switch is intermittently operated, said first third and fourth branches conduct current for energizing said filament and producing an alternating potential in said first winding, inducing a stepped-up ignition potential in said second winding, which is coupled to said lamp, and rectified by said diode,
• when said solid state switch is nonconductive, said first and second branches ballast and conduct current from said rectifier bridge and filter capacitor for energizing said lamp for normal running operation;
• and
• said control means in said high illumination level, maintaining said solid state switch in intermittent operation until said lamp has started and in said non-conducting state thereafter;
• and in said low illumination, maintaining said solid state switch in a nonconductive state;
• and
• F. a rectifier device having its anode coupled to said node and its cathode coupled to said third plug terminal for half-wave conduction through said filament and a portion of said rectifier bridge to said second bridge input terminal for providing filamentary illumination in said low illumination level.