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Involving the emission of electrons from a heated electrode.

Closeup of the filament in a low pressure mercury gas-discharge lamp showing white thermionic emission mix coating on the central portion of the coil. Typically made of a mixture of barium, strontium and calcium oxides, the coating is sputtered away through normal use, eventually resulting in lamp failure.

Involving the emission of electrons from a heated electrode.

One Edison effect bulb consisted of an evacuated bulb with an externally-wired electrode such as a metal plate in this example (variants used platinum foil or extra wire instead) isolated from the carbon filament (hairpin-shaped in this example).

Involving the emission of electrons from a heated electrode.

Edison's circuit configured his bulb (large circle) such that its electrode was in series with an ammeter (A) to measure conventional current and a voltage source (separate from the power source heating the filament) to bias the electrode either positively (in which case electrons were attracted and flowed along the arrows from the filament through the partial vacuum to the electrode) or negatively (which resulted in no measurable current). We now know that in addition to carbon molecules, the filament was emitting electrons, which have negative charge and thus are attracted to a positively-charged electrode but not a negatively-charged electrode.