Lamp control and lamp switch circuit for controlling light balance

Claim 1

A lamp control circuit for maintaining balance of light intensity output of long multi-vapor arc lamps comprising: a. a long multi-vapor arc lamp mounted for exposure; b. light chopper means for exposing a light sensitive element to light intensity output from opposite ends of said lamp at a constant frequency, said light chopper means comprises chopper driver means for driving said light chopper means to thereby expose said light sensitive element at said constant frequency and providing a reference signal for reference signal means; c. means for detecting said light sensitive element output signals to thereby provide an output signal proportional to light intensity imbalance end-to-end of said lamp; d. tuned amplifier means for amplifying said imbalance signal between a narrow bandwidth near said constant frequency; e. phase converter means for converting said imbalance signal into two signals φ 1 and φ 2 of equal amplitude separated in phase by 180°, said signals φ 1 and φ 2 amplitude is proportional to said imbalance signal; f. said reference signal means in (b) above comprising (i) filter means for filtering said reference signal (ii) phase-splitter means for splitting said reference signal and thereby making available two signals of equal amplitude separated in phase by 180° (iii) squaring and inverter means for squaring said reference signals from said phase-splitter to provide a squared signal REF means and developing another squared signal REF of the same amplitude as said squared signal REF but separated in phase by 180° and h. phase amplitude detector means for providing an output signal indicative of which end of said lamp is brighter, said phase amplitude detector output signal results from said imbalance signals φ 1 and φ 2 and is controlled by said squared reference signals REF and REF.