Ceramic Metal Halide Lamps; a World of Lighting

摘要

High pressure discharge lamps are well-known for their high luminances and efficacies in combination with long life-times. Good colour rendering is of vital importance for high-end applications. These lamps are used in applications ranging from street and outdoor lighting, shop and accent lighting and projection systems as well as high-bay industrial and front light automotive applications. Optimizing these high pressure discharge lamps for each application has led to a large family of such lamps. Well-known members of this family of high pressure discharge lamps are the high pressure mercury lamp, the high pressure sodium lamp and a large number of metal halide lamps with different fillings as well as with different envelope materials, i.e. quartz as well as polycrystalline alumina (PCA) ceramic. Typical lamp powers for the high pressure discharge lamps go from 20W to several kW. The high pressure mercury lamp is one of the oldest members of the family. In metal halide lamps additional light emitting elements are added to a high pressure mercury discharge: to fill the gaps in the visible spectrum of the mercury discharge other metals are added in the form of a metal halide. The use of metal halides instead of pure metal additions is based on arguments of (usually) higher vapour pressures for the halides as well as on the fact that the metal halide molecules are chemically less aggressive towards the envelope material.