Mercury free discharge lamp with zinc iodide

A mercury free discharge lamp for operation at approximately 42 volts AC, comprising:

• a double ended quartz envelope defining an enclosed volume of 18 to 42 cubic millimeters, the enclosed volumes containing neither mercury nor a mercury halide;
• a first electrode sealed through the quartz envelope and contacting the enclosed volume;
• a second electrode sealed through the quartz envelope and contacting the enclosed volume;
• a xenon fill gas in the enclosed volume having a cold pressure of 0.6 to 1.22 megapascals;
• a first fill component in the enclosed volume including sodium iodide with a concentration of from 5.0 to 5.7 micrograms per cubic millimeter and scandium iodide with a concentration of from 2.7 to 3.3 micrograms per cubic millimeter;
• and
• a second fill component in the enclosed volume including zinc iodide with a concentration of 2 to 6 micrograms per cubic millimeter.

A method for controlling the voltage of a mercury free metal halide lamp without substantially changing a visible spectrum thereof, comprising the steps of:

• providing a double ended quartz envelope defining an enclosed volume of 18 to 42 cubic millimeters;
• sealing a first electrode through the quartz envelope and contacting the enclosed volume;
• sealing a second electrode through the quartz envelope and contacting the enclosed volume;
• providing an inert fill gas of xenon in the enclosed volume having a cold pressure of 0.6 to 1.22 megapascals;
• providing a first fill component in the enclosed volume including sodium iodide with a concentration from 5.0 to 5.7 micrograms per cubic millimeter of the enclosed volume, and scandium iodide with a concentration of from 2.7 to 3.3 micrograms per cubic millimeter of the enclosed volume, but not including mercury or a mercury halide otherwise resulting in a first visible spectrum having a first spectral integral from 350 to 800 nanometers;
• and
• adjusting a concentration of zinc iodide in the enclosed volume between 42 to 85 micrograms per cubic millimeter of the enclosed lamp so that the lamp voltage correspondingly varies between 42 and 85 volts and provides a second visible spectrum having a spectral integral from 350 nanometers to 800 nanometers not different from the first spectral integral by more than five percent of the first spectral integral.

A method of controlling the voltage of a mercury free metal halide lamp without substantially changing the visible spectrum produced, comprising steps of:

• providing a double ended quartz envelope defining an enclosed volume;
• sealing first and second electrodes through the quartz envelope and contacting the enclosed volume;
• providing an inert fill gas in the enclosed volume having a cold pressure of more than 0.6 megapascals;
• providing a fill component in the enclosed volume including a metal halide, but not including mercury or a mercury halide otherwise resulting in a first visible spectrum having a first spectral integral from 350 nanometers to 800 nanometers;
• and
• adjusting a concentration of zinc iodide in the enclosed volume between 2 to 6 micrograms per cubic millimeter so that the lamp voltage correspondingly varies between from the voltage of operation without the zinc iodide (undoped voltage) and approximately half the undoped voltage, and provides a second visible spectrum having a second spectral integral from 350 nanometers to 800 nanometers not different by more than five percent of the first spectral integral.