Incandescent Arc Lamps

Incandescent Arc lamps are discharge lamps whose light is produced not by the electrical discharge between the electrodes, but by the incandescence of the electrodes themselves. As such they combine the advantages of the good colour rendering properties of incandescent lamps, with the small source size of short-arc discharge lamps. The original electrode material was tungsten, but this was later supersed in the higher power lamps by zirconia, which can be operated at higher colour temperature and produces a whiter light. Tungsten continued to be used however in the smaller power lamps, owing to the difficulty of making sufficiently small diameter zirconia electrodes.

Being based on the incandescence of a heated body, their efficacy is rather low. The temperature can be raised only slightly higher than that in an incandescent lamp due to the problems of electrode evaporation, and blackening of the bulb envelope. This also limits the surface brightness of the electrodes. This category of lamps has now been rendered completely obsolete, following the development of short arc xenon discharge lamps which offer higher brightness with only very minor sacrifices in colour quality.

Tungsten Arc



Point o'lite Tungsten Arc Projection lamp
c. 1950



Photo-micrographic Tungsten Arc source

Zirconia Arc



B25 Zirconium oxide incandescent arc
c. 1960



K300 Zirconium oxide incandescent arc
c. 1965