Flat circular foil-filament lamp
BACKGROUND 
     The invention relates to electric incandescent lamps having flat foil filaments suspended between a center post conductor and a ring conductor. 
     Prior art includes U.S. Pat. No. 1,305,295 by McKay which features a flat circular foil filament mounted between grooved lead-in members on opposite sides of the filament, U.S. Pat. No. 2,319,338 by Mulder which features ring conductors supported by vertical post conductors, U.S. Pat. No. 617,725 by Goddard which features a grooved heat element with integral projections on the edges thereof, U.S. Pat. No. 3,788,721 of Vause featuring a metal web element, and U.S. Pat. No. 4,144,473 of Almer which features a hollow cylindrical filament with perforations. 
     SUMMARY 
     The invention is designed for use with a conical beam concentrator with a circular planar face perpendicular to the circular beam emitted by the foil filament of the lamp. The lamp and the concentrator are used together in a copending application of a Beam Ignitor which emits a concentrated beam into the combustion chamber of an internal combustion engine as means of igniting the compressed gases therein. 
     The patentable features of the invention are the perforated foil filament and the center post conductor and the ring conductor which serve as mounting means. 
    
    
     DRAWINGS 
     FIG. 1 is an elevation of the foil-filament lamp. 
     FIG. 2 is a plan view of the foil filament mounted inside the ring conductor. 
    
    
     DESCRIPTION 
     FIG. 1 is an elevation of the flat circular foil-filament lamp with the planar circular perforated foil filament 1 suspended by mounting tabs 2 inside ring conductor 3 between front transparent bulb wall 4 and reflective rear plate 5. Current flows from a central post conductor 6 through filament 1 to ring conductor 3 to four peripheral post conductors 7 to bulb base 8. 
     Foil filament 1 is a foil of suitable high temperature metal which incandescences without melting. The filament is mounted in the horizontal plane of the bulb, and its center occupies the vertical axis of the bulb. 
     Sixteen arcuate perforations 9 are disposed in a circular pattern between the center and the perimeter of foil filament 1. Eight arcuate indentations 10 are located inside the circumference of the filament between mounting tabs 2. The purpose of the perforations 9 and indentations 10 is to permit an increase in the circumference of the filament without increasing the area thereof so that a wider beam can be emitted. 
     Foil filament 1 is supported in the central post conductor 6, which is a rigid straight steel rod mounted in bulb base 8 and occupying the vertical axis of the bulb, and around the circumference by mounting tabs 2, which are integral radial extensions of the filament. Mounting tabs 2 are curved around ring conductor 3, which is a rigid annular steel rod concentric to the filament. 
     The four peripheral post conductors 7 are rigid angular steel rods welded to the inside of ring conductor 3 as means of supporting the conductor. Peripheral post conductors 7 are mounted in bulb base 8 as shown in FIG. 1. 
     The reflective rear plate 5 is mounted on peripheral post conductors 7. The purpose of the reflective plate is to receive and return heat to the filament as means of increasing the incandescence of the filament. The rear plate also reflects light from the rear of the filament outward through the perforations 9 and indentations 10 and thereby increases the intensity of the beam emitted by the filament. 
     The bulb is a sealed evacuated glass chamber formed by front bulb wall 4, cylindrical ball 11, conical bulb wall 12, and bulb base 8.