Infrared continuum radiation from metal halide high intensity discharge lamps

Summary form only given. Understanding continuum radiation mechanisms in metal halide high intensity discharge (MH-HID) lamps is a valuable step toward reducing near infrared (IR) power losses in these lamps. Lighting consumes 25% of all electrical power. Improving the efficiency of the widely used MH-HID lamps would be significant now, and more important in the future because the use of MH-HID lamps is growing. The near IR radiation from MH-HID lamps is typically composed of a broad, strong continuum (>50% total) and atomic lines (<50% total). Features that are clearly molecular are rare and weak. The analysis of these lamps is complicated due to the de-mixing of additives. Radial cataphoresis from the plasma and thermal diffusion from large temperature gradients de-mixes additives while free convection and ordinary diffusion mix additives. Steady-state additive densities are determined by a balance among these processes. The Hg produces most of the arc density and pressure while the additives contribute most of the free electron (e-) density and much of the radiation. We are studying the near IR continuum from a MH-HID lamp. The line width of the resonance broadened Hg 1014 nm line is used to find the arc core Hg density. Absolute radiance measurements on optically thin, near IR Hg lines are Abel inverted to find the temperature as a function of radius. The electron density is determined from Dy I and Dy II lines using a Saha analysis. Our absolute near IR continuum measurements are compared to radiation transport simulations using the measured Hg density, temperature data, and e-density as inputs. Our code incorporates accurate e- + Hg atom bremsstrahlung coefficients from corrected phase-shift calculations. Recent work has shown that the near IR continuum from pure Hg lamps is dominated by e- + Hg atom bremsstrahlung radiation over a pressure range from 8 bar to 230 bar. The mechanism(s) producing the near IR continuum from MH-HID lamps will be determin- d in our work