Operating wall temperature and electrode separation are important factors in the design of efficient high-pressure sodium lamps. The authors have measured and calculated how the arc efficacy varies with wall temperature and input power per unit length. In their experiments they controlled the wall temperature by passing gases with different thermal conductivities over the arc tube. Their experiments showed that the arc efficacy increases at rates of 3.75+or-0.15% per 100K rise in wall temperature and 3.5+or-0.3% per 1 Wmm-1 increase in electrical power input. The corresponding calculated average rates are 2.1% per 100K and 1.7% per 1 Wmm-1. The satisfactory agreement of their experiments with their calculations resolves a discrepancy between their computer model predictions and those of Waymouth and Wyner (1981). Their two-zone model predicted that the efficacy decreases as the electrical power input increases. Although they have found that the proportion of the total radiation emitted in the D-lines decreases as the power input increases, this is more than compensated by an increase in the total radiated power at the expense of thermal conduction.
Measurements of the electric field and of the voltages of very short arc high-pressure sodium discharges (arc tube internal diameter 7.4 mm) have been used to estimate the electrode fall in high-pressure sodium lamps. These data are needed for the design of new ratings of high-pressure sodium lamp. Two methods have been used to avoid the systematic errors in field which result from depletion of the amalgam of sodium at high liquid amalgam temperatures. The electrode voltage fall is approximately independent of electrode construction for emitter coated electrodes at 4 ± 1 V. For pure tungsten electrodes it is 8 ± 1 V. The electrode fall is independent of discharge currents within the range 1-4.45 A.
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.
As new low power ratings of high pressure sodium lamps were designed and developed it was found that lamp lives were unexpectedly short compared with higher power ratings. The principal feature of failed lamps was extensive blackening of the arc tube with emitter material from the electrodes. Improvements to electrode construction and emitter processing offered some improvements but lamp lives were still not satisfactory. A detailed study was made of the processes occurring in the region of the electrode when the lamps were started. This revealed that sodium amalgam in electrical contact with electrode assemblies was causing the lamps to act temporarily as rectifiers, for time periods of up to two minutes, after the lamps were switched on. A new type of end plug was designed to prevent electrical contact between the sodium amalgam and the electrode assembly. Optimised 70W high-pressure sodium lamps made with this new end plug have been found to live six times longer than lamps containing the usual end construction.
The paper describes a concise experimental procedure for the rapid design of any new rating of lamp, with particular emphasis on low power lamps. Information, in some cases obtained from 400 W lamps, has been used to reduce the number of free variables associated with the design of a lamp from 11 to three. Experiments in which the amalgam temperature is altered in an indium bath are carried out to optimize the lamp and ballast simultaneously. Nine such experiments give six possible designs for any new rating of lamp, and fix the ballast impedance needed for correct operation. From these six designs, one lamp may be chosen to satisfy best the main criteria of good colour, long life, high efficacy, ease of manufacture and commercial considerations.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.