Evaluation of Tungsten Cluster Radiation Dependent on Various Metal Halides

Abstract

Tungsten cluster lamps are expected to yield high efficiency and excellent color rendering. However, a regenerative halogen cycle is required to form and maintain the small clusters within the microwave-excited high-pressure discharge. Metal halides play an important role in building the halogen cycle, but we still do not know how the metal halides affect the radiation characteristics of the tungsten clusters. We investigated the spectral radiant exitance, the luminous flux, and the color temperature of the tungsten cluster radiation in various metal halides, such as NaCl, KCl, CsCl, NaBr, KBr, CsBr, NaI and KI. The radiation from the tungsten clusters yielded a continuous spectrum with a maximum between 650 and 700 nm, although the spectra were dependent on the type of metal halide used. The luminous fluxes in the metal alkali bromides were twice as large as those in the metal alkali chlorides and iodides. Also, the luminous fluxes in the sodium halides were twice as large as those in the potassium halides, and four times as large as those in the cesium halides. From those results, we confirm that NaBr is suitable as a metal halide in tungsten cluster lamps.