Air filter control

Claim 1

IN AN AIR FILTERING APPARATUS INCLUDING A FILTER MEDIA SUPPLY ROLL TO RECEIVE A ROLL OF FILTER MEDIA, A FILTER MEDIA TAKE UP ROLL TO RECEIVE FILTER MEDIA FROM SAID SUPPLY ROLL, AN AIR FILTERING ZONE DISPOSED BETWEEN SAID SUPPLY ROLL, AND SAID TAKE UP ROLL, AND FILTER MEDIA EXTENDING FROM SAID MEDIA SUPPLY ROLL ZONE THROUGH SAID AIR FILTER ZONE TO SAID FILTER MEDIA TAKE-UP ROLL SO AIR TO BE TREATED PASSES THROUGH SAID FILTER MEDIA IN SAID AIR FILTER ZONE, AN AIR FILTER MEDIA ADVANCE CONTROL SYSTEM IN WHICH THE ADVANCE OF SAID MEDIA FROM SAID SUPPLY ROLL TO SAID TAKE-UP ROLL IS INITIATED UPON REDUCTION IN LIGHT TRANSMITTING QUALITY OF SAID MEDIA INCLUDING: AN ELECTRIC LIGHT SOURCE OF CONTROLLED INTENSITY DISPOSED ON ONE SIDE OF FILTER MEDIA, AND LIGHT-RESPONSIVE MEANS DISPOSED ON AN OPPOSITE SIDE OF SAID FILTER MEDIA FROM SAID LIGHT SOURCE FOR CONTROLLING SAID CURTAIN ADVANCE; AN ELECTRIC MOTOR DRIVINGLY CONNECTED TO SAID TAKE-UP ROLL TO EFFECT THE ADVANCE OF SAID MEDIA; AN ENERGIZING CIRCUIT TO ENERGIZE SAID MOTOR TO DRIVE SAID TAKE-UP ROLL INCLUDING NORMALLY OPEN FIRST SWITCH MEANS AND NORMALLY OPEN SECOND SWITCH MEANS; SAID FIRST SWITCH MEANS BEING OPERABLE TO A CLOSED POSITION IN RESPONSE TO A REDUCTION IN LIGHT RECEIVED BY SAID LIGHT-RESPONSIVE MEANS BELOW A PREDETERMINED VALUE; AND SAID SECOND SWITCH MEANS BEING OPERABLE TO A CLOSED POSITION IN RESPONSE TO ENERGIZATION OF SAID LIGHT SOURCE WHEREIN SAID MOTOR IS ENERGIZED WHEN SAID FIRST SWITCH AND SAID SECOND SWITCH ARE IN CLOSED POSITION.