Differential output tubular incandescent lamp

Claim 1

A DIFFERENTIAL OUTPUT TUBULAR INCANDESCENT LAMP COMPRISING AN ELONGATED TUBULAR ENVELOPE OF RADIATION-TRANSMISSIVE MATERIAL, LEAD-IN CONDUCTORS SEALED IN AND EXTENDING FROM RESPECTIVE ENDS OF SAID ENVELOPE, AN INCANDESCIBLE COILED WIRE FILAMENT EXTENDING LONGITUDINALLY OF SAID ENVELOPE AND ELECTRICALLY CONNECTED SOLELY AT ITS ENDS TO RESPECTIVE AND LEAD-IN CONDUCTORS, SAID FILAMENT BEING FORMED OF A MULTIPLICITY OF HELICALLY COILED SEGMENTS OF CLOSELY SPACED WIRE TURNS OF SUBSTANTIALLY UNIFORM PITCH SPACED APART LONGUTIDINALLY BY GENERALLY STRAIGHT SECTIONS OF THE FILAMENT WIRE, THE RELATIVE LENGTHS OF COILS SEGMENTS AND SPACES BEING VARIED SUCH THAT THE TOTAL LENGTH OF COILED SEGMENTS PER UNIT LENGTH OF ENVELOPE IS SUBSTANTIALLY GREATER AT THE ENDS OF THE ENVELOPE THAN AT THE CENTRAL PORTION OF THE ENVELOPE TO THE EXTENT THAT ABOUT ONE-FOURTH OF THE OVERALL FILAMENT LENGTH AT EACH END THEREOF CONTAINS TOTAL LENGTS OF COILED SEGMENTS AMOUNT ING TO AT LEAST ABOUT TWO-THIRDS OF THE TOTAL COILED SEGMENT LENGTHS IN THE CENTRAL HALF OF THE FILAMENT LENGTH WHEREBY MORE RADIANT ENERGY IS PRODUCED IN THE SAID ENDS THAN IN THE SAID CENTRAL PORTION OF THE ENVELOPE.