High pressure mercury vapor discharge lamp containing zirconium iodide

Claim 1

A discharge lamp for producing a substantially continuous radiation spectrum in the visible range, said lamp adapted to be operated with a predetermined power input and comprising: a radiation transmitting elongated arc tube enclosing a predetermined volume; a light transmitting envelope spaced from and surrounding said arc tube; arc supporting electrodes disposed within said arc tube adjacent the ends thereof; lead-in conductors connected to said electrodes and sealed through said arc tube; and a discharge sustaining filling within said arc tube, said discharge sustaining filling comprising, a minor quantity of inert ionizable starting gas, mercury in an amount of from about 2.0 to 4.0 milligrams per cubic centimeter of arc tube volume which when fully vaporized during normal operation of the lamp will provide a predetermined mercury vapor pressure within said arc tube, a combined quantity of sodium iodide and thallium iodide of from about 1.0 to 2.5 milligrams per cubic centimeter of arc tube volume, and zirconium iodide in an amount of from about 0.03 to 0.3 milligrams per cubic centimeter of arc tube volume whereby upon full vaporization of said mercury and substantial vaporization of said sodium iodide, thallium iodide and zirconium iodide a continuous radiation spectrum is produced.