A variation of the incandescent lamp did not use a hot wire filament, but instead used an arc struck on a spherical bead electrode to produce heat. The electrode then became incandescent, with the arc contributing little to the light produced. Such lamps were used for projection or illumination for scientific instruments such as microscopes. These arc lamps ran on relatively low voltages and incorporated tungsten filaments to start ionization within the envelope. They provided the intense concentrated light of an arc lamp but were easier to operate. Developed around 1915, these lamps were displaced by mercury and xenon arc lamps. COUNT 4
QSN1 What did an alternate version of the incandescent lamp substitute for a wire filament? ANS1 an arc struck on a spherical bead electrode QSN2 What was a common application for this type of bulb? ANS2 scientific instruments such as microscopes QSN3 When was this style of lamp developed? ANS3 1915 QSN4 What displaced this style of lamp? ANS4 mercury and xenon arc lamps