Effect of sodium/mercury ratio and amalgam temperature on the efficacy of 400 W high-pressure sodium lamps

Abstract

400 W high-pressure sodium arc tubes containing different quantities of mercury in the sodium/mercury amalgam were placed with one end submerged in a bath of molten indium which controlled the temperature of the amalgam. For a series of different amalgam temperatures the following parameters were measured on 240 V supply: voltage, current, power input, self-reversal width and luminous flux. Information taken from these graphs and replotted as a function of the amalgam composition provided the amalgam temperature and amalgam composition for maximum efficacy at 400 W. A broad maximum was observed with a peak of 116:t 1 tm W- 1 at an amalgam temperature of -640°C with a mole fraction of sodium of 0. 7. Now these optimum conditions have been established, higher efficacies still have been obtained using superior arc tube materials.