The Standard Electrical Dictionary

1. Lamp, Semi-incandescent

   A lamp partaking of the characteristics of both arc and incandescence; a lamp in which the imperfect contact of two carbon electrodes produces a part of or all of the resistance to the current which causes incandescence. The usual type of these lamps includes a thin carbon rod which rests against a block of carbon. The species of arc formed at the junction of the two heats the carbons. Sometimes the upper carbon or at least its end is heated also by true incandescence, the current being conveyed near to its end before entering it. Semi-incandescent lamps are not used to any extent now.