1919 and 1935

Further developments allowed ductile tungsten to be single or double coiled, effectively increasing the length of the filament (and the wattage) without taking up more space inside the light bulb.  Thus these metallic looking filaments are normally short, about one inch long. (Note: See A43 to distinguish a single-coiled filament from a double-coiled filament.)  They are mounted either horizontally in a semi-circular fashion on the two lead wires (bi-post mounting) and two or more wire supports attached to the shank, stem press, or button rod or diagonally or vertically from one longer lead-in wire to the shorter lead-in wire [see A118].  Single coiled tungsten filaments were first developed in 1919 and double coiled filaments came along in 1935. These are the filaments used in out standard household light bulbs today.  Light bulbs have not been much improved on, if at all, since the days of the Great Depression when Franklin Delano Roosevelt was president. Think about that! ”

END: Evolution of Filaments

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