Holography as a diagnostic technique in the study of lamps and lighting

Abstract

Internal convection currents within the gasfilling of incandescent and tungsten-halogen lamps predominantly govern the transportation of evaporated tungsten, and it is essential to try to visualise these to increase understanding of the mechanisms involved. Holography has helped gas temperature and density profiles to be explored. The technique of producing two holograms on a single photographic plate, through a lens, gives a method of viewing optical path differences within the gasfilling of a lamp during operation; these holograms can be viewed in a parallel beam of incoherent white light. A photographic process has also been used which gives a high diffraction efficiency and obviates the difficulty of plate fog caused by lighting the filament. These holograms permit a narrow section through a lamp to be viewed which should reduce the difficult problem of interpreting three-dimensional interference fringes. The technique should also be useful for discharge lamps and fittings diagnostics.