Incandescent Point-Source Lamps

Updated
10-X-2020
Incandescent point-source lamps contain a tiny body which is brought to incandescence by methods other than the passage of an electrical current through a filament. The incandescent target may be heated either by arranging it as the electrode of an electrical discharge, or by radio-frequency induction. 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 The original electrode material was tungsten, but this was later superseded in the higher power lamps by zirconium oxide, which can be operated at higher colour temperature and produces a whiter light.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. A later development saw the use of even more refactory tantalum carbide, this being heated by RF induction.

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 was 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 Incandescent Arc

Ediswan

150CP
Point o'lite Tungsten Arc Projection lamp
~1950

GE

330W
Photo-micrographic Tungsten Arc source
1958

Philips

58W
Tungsten-Neon Incandescent Arc
1963

Zirconium Incandescent Arc

Sylvania

25W
B25 Zirconium oxide incandescent arc
~1960

Sylvania

300W
K300 Zirconium oxide incandescent arc
~1965
   

Tantalum Carbide Induction

Sylvania

AN-2 Radio Frequency Induction Incandescent
~1955