Some Factors Affecting the Lumen Maintenance of Dysprosium-Thallium-Sodium-Cesium Iodide Arc Lamps

Abstract

Experimental investigations of the lumen maintenance in dysprosium-thallium-sodium-cesium iodide arc lamps are described. Vertically burning 400 watt metal halide lamps were examined under the condition of continuous operation
The lamps having low lumen maintenance were characterised as follows:
(1) High reignition voltage at early stage of life,
(2) appearance of mercuric iodide in the inner quartz tube,
(3) deposition of silicon-dysprosium oxide compound on the coldest wall of the inner quartz tube after hundreds-hour operation,
(4) deposition of silicon on the tip of the lower electrode after hundreds hour operation.
Lamps with high reignition voltage contain impurity gas of hydrogen in the inner quartz tube with high partial pressure.
It is concluded from the above mentioned results that the most important factor in lumen maintenance of the dysprosium-thallium-sodium-cesium iodide arc lamps is the chemical reaction between liquid dysprosium triiodide and quartz tube.