identify your lightbulb > bulb identification key


STEP 7: Filament Connections to Inner Leads


Select the option most resembling your bulb from the drop-down menu to proceed to the next step. Please consult "option descriptions" for detailed info.


[The drop-down menu can be re-set by refreshing your browser window.]


FULL OPTION DESCRIPTIONS / IMAGE GLOSSARY: [Option titles are also linked to proceed to the next step.]


OPTION A: Each end of the carbon thread filament is connected to the inner leads by both carbon paste above and copper joints or clamps with small screws below. Look for a long grayish bead and tiny copper plates with screws near the junction of each inner lead and the filament. This method of fastening the filament to the inner leads was used for Edison’s first successful electric lamp in 1879. [451]


OPTION B: The individual connections between each end of the filament and the platinum inner lead wire are crudely fastened together by delicate copper clamps with small screws. This method of fastening the filament to the inner leads was used from 1879 to 1881. [452]


OPTION C: The individual connections between each end of the filament and the platinum inner lead wire are crudely connected with a tiny folded piece of copper and copper-plated together. This method of fastening the filament to the inner leads was used from 1881 to 1886. [453]


OPTION D: Each end of the filament is connected to the platinum lead in wires by carbon paste joints. Look for a large or elongated black bead at the junction of each inner lead and the filament.  This method of connecting the filaments was introduced in 1886.  They are still referred to as carbon clamps, even though technically they are not clamps but beads of paste. [454]
OPTION E: Each end of the filament is connected to platinum lead-in wires by carbon paste joints.  Look for carbon paste beads at the junction of each inner lead and the filament. These are carbon paste clamps. But the stem is now shorter, resulting in shorter platinum lead-in wires. Shorter stems first came into use in 1889. [455]
OPTION F: Each end of the thin spiral thread filament is connected to inner leads by carbon paste joints. Look for a long black bead at the junction of each inner lead and the filament.  Filament is almost perfectly symmetrical.  This is the modern method of clamping filament ends to the inner leads that was first used in 1886. [456]

Feel Lost? Returning to Step 3 and re-starting the option process will often help you correct the misstep.

Pathway History:
  thomas edison > website navigation thomas edison > home page thomas edison > timeline : early life thomas edison > timeline : inventing the incandescent lamp thomas edison > timeline : after lighting thomas edison > timeline : legacy of invention thomas edison > classroom thomas edison > interactive modules