Relationship between efficacy, arc tube temperature and power dissipation in a high-pressure sodium lamp

Abstract

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.

The Chemical Composition of Plasmas Generated in High Pressure Discharge Lamps Containing Tin and Sodium Halides

“…Thus, for the SnC12 + NaC1 system E(Na) = p(NaC1 + Na2C12 + NaSnCl~)/p~ [3] The sodium enhancement decreases with increasing temperature.…”

“…For each system we define the sodium enhancement, E(Na), as the sum of the partial pressures of all sodium containing species divided by the vapor pressure of the pure sodium halide at the same temperature. Thus, for the SnC12 + NaC1 system E(Na) = p(NaC1 + Na2C12 + NaSnCl~)/p~ [3] The sodium enhancement decreases with increasing temperature.…”

“…A knowledge of the temperature profile enables us to predict the electrical and spectral characteristics of the arc. We have used our model to investigate the variation of efficacy for a high pressure sodium lamp with arc tube bore and current (2), and with arc tube temperature and electrical power dissipation (3). The model has thus contributed directly to the development and improvement of high pressure sodium lamps.…”