Metal-halide discharge lamps

Claim 2

A metal-iodide discharge lamp comprising: a quartz discharge tube; two main electrodes; an auxiliary electrode; two power-input conductors; a thermal switch; and a current-limiting impedor; the said electrodes being mounted in the discharge tube with one of the main electrodes and the auxiliary electrode adjacent one another and remote from the other main electrode; one of the said power-input conductors being connected to the said one main electrode; the other power-input conductor being connected to said other main electrode, and through the thermal switch and the current-limiting impedor to the auxiliary electrode, the said impedor being in series with the said switch; and said auxiliary electrode being electrically isolated from said main electrodes upon opening of said thermal switch.

Claim 3

A lamp as claimed in claim 1, wherein the thermal switch is a bi-metallic switch.

Claim 4

A lamp as claimed in claim 1, wherein the current-limiting impedor is a resistor.

Claim 5

A lamp as claimed in claim 1, wherein the discharge tube contains proportions of mercury iodide and sodium iodide.

Claim 6

A discharge lamp comprising: a quartz discharge tube; two main electrodes; an auxiliary electrode; two power-input conductors; a thermal switch; and a current-limiting impedor; the said discharge tube containing a porportion of at least one metal halide; the said electrodes being mounted in the discharge tube with one of the main electrodes and the auxiliary electrode adjacent one another and remote from the other main electrode; one of the said power-input conductors being connected to the said one main electrode; the other power-input conductor being connected to the said other main electrode, and through the thermal switch and the current-limiting impedor to the auxiliary electrode, the said impedor being in series with the said switch; and said auxiliary electrode being electrically isolated from said main electrodes upon opening of said thermal switch.

Claim 7

A discharge lamp comprising: a quartz discharge tube; two main electrodes; an auxiliary electrode; two power-input conductors; a thermal switch; and a current-limiting impedor; the said discharge tube containing a porportion of at least one metal halide; the said electrodes being mounted in the discharge tube with one of the main electrodes and the auxiliary electrode adjacent one another and remote from the other main electrode; one of the said power-input conductors being connected to the said one main electrode; the other power-input conductor being connected to the said other main electrode, and through the thermal switch and the current-limiting impedor to the auxiliary electrode, the said impedor being in series with the said switch; and said auxiliary electrode being electrically isolated from said main electrodes upon opening of said thermal switch.

Claim 8

A discharge lamp as claimed in claim 5, wherein the or each metal halide is a metal iodide.

Claim 9

A discharge lamp as claimed in claim 6, wherein the or at least one metal iodide is an alkali metal iodide.

Claim 10

A discharge lamp as claimed in claim 5, wherein the lamp consumes 1000 watts when operating.

Claim 11

A metal iodide discharge lamp comprising: an outer envelope of borosilicate glass; a quartz discharge tube mounted in the outer envelope; an insert gas filling in the space between the said outer envelope and the discharge tube; two main and one auxiliary electrodes mounted in the discharge tube with one of the main electrodes and the auxiliary electrode adjacent one another and remote from the other main electrode; two power-input conductors passing into the said outer envelope with one being connected to the said one main electrode, and the other being connected to the said other electrode; a current-limiting impedor; a thermal switch mounted adjacent the discharge and connected to the said impedor with the said other power-input conductor being connected to the auxiliary electrode through the said impedor and the said switch in series; said auxiliary electrode being electrically isolated from said main electrodes upon opening of said thermal switch; and the discharge tube containing a filling having as its constituents mercury, mercury iodide, sodium iodide, scandium metal, and argon.

Claim 12

A metal iodide discharge lamp comprising: an outer envelope of borosilicate glass; a quartz discharge tube mounted in the outer envelope; an insert gas filling in the space between the said outer envelope and the discharge tube; two main and one auxiliary electrodes mounted in the discharge tube with one of the main electrodes and the auxiliary electrode adjacent one another and remote from the other main electrode; two power-input conductors passing into the said outer envelope with one being connected to the said one main electrode, and the other being connected to the said other electrode; a current-limiting impedor; a thermal switch mounted adjacent the discharge and connected to the said impedor with the said other power-input conductor being connected to the auxiliary electrode through the said impedor and the said switch in series; said auxiliary electrode being electrically isolated from said main electrodes upon opening of said thermal switch; and the discharge tube containing a filling having as its constituents mercury, mercury iodide, sodium iodide, scandium metal, and argon.

Claim 13

A discharge lamp as claimed in claim 9, wherein the thermal switch is a bi-metallic switch which opens at a first temperature thereof and closes at a second temperature thereof.

Claim 14

A discharge lamp as claimed in claim 9, wherein the said temperatures are substantially the same.

Claim 15

A discharge lamp as claimed in claim 9, wherein the said one main electrode is connected to the said one conductor through a metal-to-quartz seal formed of molybdenum, and the said auxiliary electrode is connected to the said series connected switch and impedor through another metal-to-quartz seal formed of molybdenum.

Claim 16

A discharge lamp as claimed in claim 12, wherein the said metal-to-quartz seals are molybdenum foils.

Claim 17

A discharge tube as claimed in claim 1, wherein the said one main electrode and the said auxiliary electrode are connected to respective metal-to-quartz seals formed of molybdenum.