Abstract: A power supply for a metal halide discharge lamp includes a circuit for applying a high voltage starting pulse to the arc tube of the lamp to initiate the discharge, a glow transition current to provide power transitioning the arc tube from its glow to its run mode, and a run power supply circuit to provide continuous controlled d-c current to the arc tube.

Abstract: Feedback circuitry for a charge digitizer is disclosed. The feedback circuitry includes a photo-diode coupled between the input of the integrator and the biasing voltage of the photo-diode and a pulsed light source connected to the output of the multivibrator of the digitizer. The pulsed light source is operative responsive to the output pulses of the multivibrator and will actuate the photo-diode upon each pulse to discharge the integrating capacitor. Preferably, the photo-diode is specially constructed to have a grounded guard ring separating the anode and the cathode portions of the envelope to thereby prevent unintended current flow on or through the envelope. This provides a normally open feedback circuit with current flow only during the pulsed intervals.