The author states that in recent years the emphasis in lamp development has been on innovation rather than standardisation, and that now the aim should be increased performance and operation rather than more new developments. This article compares the two common and efficient lamps: high pressure sodium and metal halide lamps. high pressure sodium lamps are compact, with improved colour rendering, and suitable for many applications. A disadvantage is difficulty in finding a discharge tube resistant to effects of sodium vapours. Tubular forms are most popular, one with an outer bulb of quartz allowing instant restarting by application of a higher voltage at both ends. Electronic ignition, though widely used, requires a short cooling period before re-ignition. In a third method,a built-in bi-metal switch induces sufficient voltage for ignition upon opening. Colour rendering depends upon ambient temperatures and loading, in inverse proportions. Metal halide lamps are also most used in tubular or double ended forms. Though the colour rendering problem is not so apparent, fillings are of a wide variety, choice depending upon the arc tube temperature with respect to the life required. The author describes a number of fillings for specific types and purposes of lamp. the author's findings are assessed in a discussion appended to the report.
Abstract