CA2112063A1 - Metal halide lamp - Google Patents
Metal halide lampInfo
- Publication number
- CA2112063A1 CA2112063A1 CA 2112063 CA2112063A CA2112063A1 CA 2112063 A1 CA2112063 A1 CA 2112063A1 CA 2112063 CA2112063 CA 2112063 CA 2112063 A CA2112063 A CA 2112063A CA 2112063 A1 CA2112063 A1 CA 2112063A1
- Authority
- CA
- Canada
- Prior art keywords
- arc tube
- titanium oxide
- metal halide
- vitreous silica
- doped
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
- H01J61/00—Gas-discharge or vapour-discharge lamps
- H01J61/02—Details
- H01J61/30—Vessels; Containers
- H01J61/302—Vessels; Containers characterised by the material of the vessel
Landscapes
- Vessels And Coating Films For Discharge Lamps (AREA)
Abstract
ABSTRACT
An arc tube for a metal halide discharge lamp is formed of titanium oxide doped vitreous silica. In one embodiment of the invention the doped vitreous silica is fused quartz made from a melt doped with TiO2. In a preferred embodiment, the concentration of titanium oxide in the vitreous silica is approximately 250 parts per million by weight. Metal halide discharge lamps utilizing arc tubes formed from the doped vitreous silica demonstrate improved lumen output and lumen maintenance. It is believed that arc tubes formed from the doped vitreous silica also suffer less sodium loss than arc tubes formed from conventional fused quartz.
An arc tube for a metal halide discharge lamp is formed of titanium oxide doped vitreous silica. In one embodiment of the invention the doped vitreous silica is fused quartz made from a melt doped with TiO2. In a preferred embodiment, the concentration of titanium oxide in the vitreous silica is approximately 250 parts per million by weight. Metal halide discharge lamps utilizing arc tubes formed from the doped vitreous silica demonstrate improved lumen output and lumen maintenance. It is believed that arc tubes formed from the doped vitreous silica also suffer less sodium loss than arc tubes formed from conventional fused quartz.
Description
2 1 ~ 2 ~ t3 3 92-1-082 PAT~N~
-- 1 -- .~
IMPROVED METAL HALIDE LAMP - ~
"'~'''~
"'~ ' `
Field of the Invention ::
. ,-..
This invention relates generally to a metal halide arc discharge lamp and, more particularly, ~o an arc discharge lamp having an improved arc tube.
Bac~ground of the Invention Metal halide arc discharge lamps are frequently employed in commercial usage because of their high luminous efficiency and long life. A typical metal halide arc .
discharge lamp includes a quartz or fused silica arc tube that is hermetically sealed within a borosilicate glass lamp envelope. The arc tube, itself hermetically sealed, has -~
tungsten elec~rode~ mounted therein and contains a fill ~:
material including mercury, metal halide additives and a rare gas to facilitate starting. In some cases, :~
particularly in high wattage lamps, the lamp envelope is ~:
filled with nitrogen or another inert gas at less than ! .:
atmospheric pressure. In other cases, particularly in low wattage lamps, the lamp envelope is evacuated.
..
..'.
92-1-Og2 21~2~3 PATENT
Sodium ~s an important constituent in mo3t high intensity metal halide arc discharge lamp~, usually ln the form of sodium iodide or sodium bromide. Sodium is used to improve the efficiency and color rendering properties of the metal halide lamps. It has long been recognized that sodium loss during operation is a problem with metal halide discharge lamps having arc tubes that contain sodium halides. As sodium is lost through the arc tube wall, iodide is freed and combines with mercury to form mercury -iodide. Mercury iodide leads to increased reignition voltages, thereby causing starting and lamp maintenance problems.
Sodium loss results from the movement or migration of sodium ions through the arc tube wall. There are two prevailing theories relating to the cause of this sodium movement. ~ first theory suggests that sodium loss is caused by the emis ion of ultraviolet ( W ) photons from the arc tube. These W photons cause electrons to be ejected from materials, such as metals, that are positioned within the outer jacket of the lamp. The electrons ejected from these materials collect on the outside surface of the arc tube and form a negatively charged layer. The build-up of negatively charged electrons along the outer surface of the arc tube attracts positively charyed sodium ions from w1thin the arc tube and enhances their migration through the quartz arc tube wall. Once the positively charged sodium ions reach the outer surface of the arc tube wall, they ara neutralized by the electrons present on the surface of the arc tube, evaporate as atoms and travel to cold spots in the lamp where they condense.
A second theory suggests that the loss of sodium from the arc tube is not primarily caused by W radiation emitted -- 2 L ~ 3 from the arc tube. Rather, this theory suggests that the loss of sodium is due to the thermal migration of ~odium ions through ~he arc tube wall during the operation of the lamp.
Despite the uncertainty as to its causation, sodium loss -from metal halide lamps having arc tubes that contain sodium halides has long been recognized as a problem.
Con~equently, a number of designs have been proposed for reducing sodium loss. In a so-called "frameless construction" disclosed in U.S. Patent No. 3,424,935 issued January 28, 1969 to Gungle et al., no frame members are located close to the arc tube. By eliminating heavy metallic support rods, by using a small diameter current return wire between the lamp base and the dome end of the arc tube, and by positioning the current return wire at a relatively large distance from the arc tube, the material from which electrons can be e~ected by W radiation is greatly reduced. However, this technique for reducing sodium loss is ineffective in small low-wattage lamps.
In U.S. Patent No. 3,988,628 issued on October 26, 1976 to Clausen, a thick coating of TiO2 is fused onto the outer surface of the fused quartz ar~ tube. ~he coating of Tio2 is reported to reduce sodium ion conductivity through the arc tube and also reduce W radiation from the arc tube to~ ;
nearly zero at wavelengths less than approximately 240nm. -However, this technique for reducing sodium loss increases the cost of producing metal halide arc tube lamps because of the added expense of~materials, labor and facilities needed for coating the arc tube.
In U.S. Patent No. 4,866,328 issued on September 12, 1989 ~o Ramaiah et al., a coa~ing of ZrO2 is provided over-~
metal surfaces positioned within the lamp envelope external ~` 2.L ~20(~
92-1-082 PA~ENT
-- 1 -- .~
IMPROVED METAL HALIDE LAMP - ~
"'~'''~
"'~ ' `
Field of the Invention ::
. ,-..
This invention relates generally to a metal halide arc discharge lamp and, more particularly, ~o an arc discharge lamp having an improved arc tube.
Bac~ground of the Invention Metal halide arc discharge lamps are frequently employed in commercial usage because of their high luminous efficiency and long life. A typical metal halide arc .
discharge lamp includes a quartz or fused silica arc tube that is hermetically sealed within a borosilicate glass lamp envelope. The arc tube, itself hermetically sealed, has -~
tungsten elec~rode~ mounted therein and contains a fill ~:
material including mercury, metal halide additives and a rare gas to facilitate starting. In some cases, :~
particularly in high wattage lamps, the lamp envelope is ~:
filled with nitrogen or another inert gas at less than ! .:
atmospheric pressure. In other cases, particularly in low wattage lamps, the lamp envelope is evacuated.
..
..'.
92-1-Og2 21~2~3 PATENT
Sodium ~s an important constituent in mo3t high intensity metal halide arc discharge lamp~, usually ln the form of sodium iodide or sodium bromide. Sodium is used to improve the efficiency and color rendering properties of the metal halide lamps. It has long been recognized that sodium loss during operation is a problem with metal halide discharge lamps having arc tubes that contain sodium halides. As sodium is lost through the arc tube wall, iodide is freed and combines with mercury to form mercury -iodide. Mercury iodide leads to increased reignition voltages, thereby causing starting and lamp maintenance problems.
Sodium loss results from the movement or migration of sodium ions through the arc tube wall. There are two prevailing theories relating to the cause of this sodium movement. ~ first theory suggests that sodium loss is caused by the emis ion of ultraviolet ( W ) photons from the arc tube. These W photons cause electrons to be ejected from materials, such as metals, that are positioned within the outer jacket of the lamp. The electrons ejected from these materials collect on the outside surface of the arc tube and form a negatively charged layer. The build-up of negatively charged electrons along the outer surface of the arc tube attracts positively charyed sodium ions from w1thin the arc tube and enhances their migration through the quartz arc tube wall. Once the positively charged sodium ions reach the outer surface of the arc tube wall, they ara neutralized by the electrons present on the surface of the arc tube, evaporate as atoms and travel to cold spots in the lamp where they condense.
A second theory suggests that the loss of sodium from the arc tube is not primarily caused by W radiation emitted -- 2 L ~ 3 from the arc tube. Rather, this theory suggests that the loss of sodium is due to the thermal migration of ~odium ions through ~he arc tube wall during the operation of the lamp.
Despite the uncertainty as to its causation, sodium loss -from metal halide lamps having arc tubes that contain sodium halides has long been recognized as a problem.
Con~equently, a number of designs have been proposed for reducing sodium loss. In a so-called "frameless construction" disclosed in U.S. Patent No. 3,424,935 issued January 28, 1969 to Gungle et al., no frame members are located close to the arc tube. By eliminating heavy metallic support rods, by using a small diameter current return wire between the lamp base and the dome end of the arc tube, and by positioning the current return wire at a relatively large distance from the arc tube, the material from which electrons can be e~ected by W radiation is greatly reduced. However, this technique for reducing sodium loss is ineffective in small low-wattage lamps.
In U.S. Patent No. 3,988,628 issued on October 26, 1976 to Clausen, a thick coating of TiO2 is fused onto the outer surface of the fused quartz ar~ tube. ~he coating of Tio2 is reported to reduce sodium ion conductivity through the arc tube and also reduce W radiation from the arc tube to~ ;
nearly zero at wavelengths less than approximately 240nm. -However, this technique for reducing sodium loss increases the cost of producing metal halide arc tube lamps because of the added expense of~materials, labor and facilities needed for coating the arc tube.
In U.S. Patent No. 4,866,328 issued on September 12, 1989 ~o Ramaiah et al., a coa~ing of ZrO2 is provided over-~
metal surfaces positioned within the lamp envelope external ~` 2.L ~20(~
92-1-082 PA~ENT
- 4 - -~
;"
to the arc tube. The ZrO2 coating prevents W photons from reaching the metal surfaces, thereby preventing any electrons from being e~ected therefrom. In addition to ZrO2, ceramic tubes or other ceramic coatings have also been used to perform this function. ~his technlque of shielding the metal surfaces within the lamp envelope suffers from disadvantages in that it increases the manufacturing costs of the metal halide lamps and may not be durable for extended burn life.
It is known to utilize titanium doped fused quartz to absorb W radiation in reprographic lamps. The reduction of W radiation in these lamps i5 beneficial hecause at some wavelengths, the W radiation produces ozone and at other wavelengths, the W radiation can damage human eyesight.
It is a general object of the present invention to provide improved metal halide arc discharge lamps.
It is a another object of the present invention to provide an improved arc tube for use in a metal halide arc discharge lamp.
It is a further ob~ect of the present invention to provide an arc discharge lamp wherein sodium loss ~rom the arc tube is relatively low. -It is a further obiect of the present invention to provide a metal halide discharge lamp having increased light output.
Summary of the Invention According to the present invention, these and other objects and advantages are achieved in an arc tube for a metal halide lamp comprising an arc tube wall formed of titanium oxide dopPd vitreous silica. The vitreous silica is formed by doping guartz sand with a titanium compound, ~! ". ' . ,-; . . ',',', , . ` -2~
92-1-082 PAT~NT
such as titanium oxide, prior to melting. The concentration of the titanium oxide dopant i in the range of one hundred and fifty to three hundred and fiPty parts per mlllion by weight~ with the preferred concentration being approximately two hundred and fifty parts per million by weight. Metal halide discharge lamps utilizing arc tubes formed from the titanium oxide doped quartz demonstrate increased lumen output and lumen maintenance.
Brief Description of the Drawinq Fig. 1 is an illustrative example of a metal halide discharge lamp;
Figs. 2(a) - 2(d) are graphs of results from a first test comparing the performance of standard production lamps with lamps having arc tubes made of quartz doped with TiO2;
Figs. 3(a) - 3(d) are graphs showing the relative concentrations of various ion species as a function of time for the lamps taken over the course of the first test; and Fig~. 4~a~ ~ 4(d) are graphs of results from a second test comparing the performance of standard production lamps wlth lamps having arc tubes made of quartz doped with TiO2. ~-Detailed Description of the Invention --The present invention is directed to an improved arc -~
tube for use in a metal halide lamp. Fiq. 1 illustrates a typical metal halide arc discharge lamp in which the present invention can be utilized. It should be understood ~hat .
Fig. 1 is provided merely for illustrative purposes and that the arc tube of the present invention can be used with any type of metal halide arc tube lamp, including those having structures that differ from the example shown in Fig. 1. In ~-Fig. 1, a lamp 2 includes a lamp envelope 4 and an arc tube ~
' . .
tû 3 6 mounted within lamp envelope 4. The arc tube 6 is a metal halide arc discharge tube having characteristics that are fully described below.
The arc tube 6 is supported within the envelope 4 via a lower support means 8 and an upper support means 10. Lower support means 8 comprises a U-shaped support made up of vertical wires 14 and 16 extending from a base wire 18. The vertical wires 14 and 16 are welded to a strap 20 tha~
supports the lower end of the arc tube 6. Upper support means 10 similarly comprises a U-shaped support made up of vertical wires 22 and 24 extending from a base wire 26. The vertical wires 22 and 24 are welded to a strap 28 that supports the upper end of the arc tube 6.
Electrical energy is coupled to the arc tube 6 through a base 28. A pair of stiff lead-in wires 30 and 32 are electrically connected to the base 28. Lead-in wire 32 is welded to base wire 18 of the lower support means 8. An additional lead-in wire 34 is electrically connected to vertical wire 16 of lower support means 8. Lead-in wire 34 :~
is connected, via a molybdenum foil 36, to an electrode 38 within the arc tube 6. A resistor 40 is attached to lead-in wire 30 and to a connector 42. Connector 42 is connected, via a molybdenum foil 44, to a starting probe 46.
At the upper end of arc tube 6, a lead-in wire 48 is attached, via a molybdenum foil 50, to an electrode 52. ~:
Lead-in wire 48 is electrically connected to stiff lead-in wire 30 through a thin conducting lead 54. The molybdenum foils 36, 44 and 50 are located in press seals at opposite ends of arc tube 6.
As s~ated above, the present invention is directed to an improved arc tube for use ln a metal halide lamp such as the one shown in F~g. 1. The arc tube of the present invention is formed of a titanium oxide doped vitreous silica. In one embodiment o~ the invention, the vitreous ~ilica i~ fused quartz that is made from a melt doped with TiO2. This doped quartz is hereafter referred to as "ozone free quartz"
because the titanium oxide dopant reduces the emission of W
radiation from the arc tube that would produce ozone. By utilizing ozone free quartz rather than conventional quartz in forming the arc tube/ it is believed that sodium loss from the arc tube is reduced ln two ways. First, the titanium oxide in the ozone free quartz may help to retard the ~ovement of sodium ions through the arc tube wall.
Second, the titanium oxide in the ozone free quartz absorbs~:
W radiation so that the amount of W radiation emitted from the arc tube is reduced. As previously stated, one theory regarding the cau~e of sodium loss in metal halide lamps suggests that W photons emitted from the arc tube cause electrons to be ejected from materials in the outer jacket, thereby generating a negativel~ chaxged layer that attracts positively charged sodium ions through the arc tube wall.
Consequently, by reducing the amount of W radiation emitted from the arc tube, it is believed that the use of ozone free quartz results in a reduction of sodium loss from the arc :-tube of the metal halide discharge lamp. -~
In order to verify the performance of the arc tubes made from ozone free quartz, a series of tests was run comparing--~
four standard production GTE M175U Metalarc lamps (utilizing ::
arc tubes made from quartz that did not contain a TiO2 --~:
dopant), with four GTE M175U Metalarc lamps having arc tubes .
made of ozone free quartz. All the test lamps were made at ~
the same ~ime as part of a single production run. The ozone:`
free quartz was made by doping the quartz sand normally utilized to form metal halide arc tubes with TiO2 prior to ~2~
melting. Thereafter, the mixture o quartz sand and TiO2 was melted and formed into arc tubes in a conventlonal manner that is known to those skilled ln the art.
The concentration of titanium oxide in the ozone free quartz utilized for the test run described above was 250 parts per million by weight. However, it is believed that the advantages of the present invention an be achieved with ozone free quartz having various other concentrations of titanium oxide within the range of 150 to 350 parts per million by weight. Additionally, although TiO2 was used as the dopant in forming the ozone free quartz, other titanium compounds could also be utilized that form titanium oxide when heated. Examples of other titanium compounds that are - ~-believed to be suitable for use as a dopant are titanium nitrate and compounds from the family of titanium alkoxides, such as tetrabutyl titanate. Similarly, although the arc tubes utilized in the test lamps were formed from doped quartz, it should be appreciated that arc tubes embodying the present invention can also be formed from other types of vitreous silica such as synthetic silica produced from silane.
Prior to forming the ozone free quartz into tubes, it was vacuum baked to a low hydroxyl content indicated by a BetaoH of 0.0005 to 0.0007 nm-l. Testing indicated that the amount of W radiation emitted from the ozone free quartz wa~ reduced to approximately zero at wavelengths below approximately 200 nm, with the 50~ W cut-off at approxim~tely 240 nm. This test verifies that the use of ozone free quartz should successfully reduce the W
radiation emitted from~the arc tube. As a result, the amount of photons available for ejecting electrons from materials in the outer jacket ~hould be ~ignificantly i! .;, " ; ~ . , ,. ,.. :, ~ 2 ~ ~ 2 ~
_ g _ .
reduced, thereby reducing sodium loss ln comparison to metal halide lamps having arc tubes formed from conventlonal fused quartz.
Figs. 2(a) - 2(d~ show a compari~on of the results of a first test comparing the performance of the four lamps having ozone free quartz arc tubes (indicated by plots 30, 32, 34 and 36) with the four standard production lamps ~-~
(indicated by plots 31, ~3, 35 and 37). Figs. 2(a)-2(d) are graphs of arc tube voltage, lumen output, color ~emperature and color rendering index, respectively, as a function of time. As can be seen from Fig. 2(b), the lamps having arc tubes made from ozone free quartz (indicated by plot 32) displayed roughly a 20~ improvement in both lumen output and lumen maintenance at 6,000 hours from the standard production lamps (indicated by plok 33). The improvemen~ in lumen output and lumen maintenance indicates that lamps utiiizing ozone free quartz arc tubes have a significant performance advankage over lamps with arc tubes made from ~onventional fused guartz.
The improvement in both lumen output and lumen maintenance was unexpected prior to conducting the above-described te~t~ The reason for the improved lumen output and lumen maintenance exhibited by the arc tubes made from ozone free quartz is not precisely known. It i5 possible that the increased sodium retention resulting from the use of the titanium oxide dopant enables the arc tubes made from ozone free quartz to have greater lumen output over a longer period of time than conventional arc tubes. It is also possible that the tLtanium oxide dopant changes the conductivity of the arc tube, thereby altering khe energy -~
balance in a manner that results in the generation of an increased amount of visible radiation. Additionally, the 92-1-082 2~G6i PA~ENT
-- 1~ --energy balance may also be altered by the conversion of W
radiation into thermal or visible radiation since the titanium oxide dopant inhibits W radiation from escaping the arc tube.
An analysis of Figs. 2(a) - 2(d) demonstrates that the lamps having arc tubes made from ozone free quartz not only -~
demonstrated improved lumen output and lumen maintenance, but also did not demonstrate any significant deficiencies with regard to other lamp characteristics. Although the lamps made with arc tubes of ozone free quartz had a higher voltage ratinq, their voltage reached a plateau at approximately 3,000 hours and thereafter remained steady while the voltage of the standard production lamps continued to rise in an undesirable fashion. The color rendering index (CRI) remained lower for the lamps utilizing the ozone free quartz arc tubes for the majority of the test. The voltage plateau and lower color rendering index for the lamps having ozone free quartz arc t~bes is believed to be thie result of a reduction in sodium loss from those arc tubes.
Figs. 3(a) - 3(d) are graphs showing the relative concentrations of various ion species as a function of time for the lamps having arc tubes made from ozone free quartz (indicated by plots 38, 40, 42 and 44) and the standard production lamps (indicated by plots 39, 41, 43 and 45).
These graphs show no major differences in the arc species contents between the groups, althouqh the iodine content of the ozone free group (indicated by plot 44) hit a plateau early while that of the control group ~indicated by plot 45) gradually dropped. The similarity of values for scandium and sodium in the two groups of lamps suggests that the higher lumen production in the group of lamps with the ozone 92-1-082 - 11 - P~TENT
free quartz arc tubes dld not result from heating of those arc tube~.
Figs. 4(a) - 4(d) illustrate the results of a second lamp test which utilized double ended lamps of a non-standard design. The control group (indicated by plots 47, ~
49, 51 and 53) utilized standard 175W production arc tubes ~-while the test group (indicated by plots 46, 48, 50 and 52) utilized lamps that were made at the same time and were identical except for the use of arc tubes formed from ozone-~-free quartz. Many of the lamps in both groups failed early in the test as a result of oxidation at the inleads of the outer jacket. However, those that survived showed that the lamps with the ozone free arc tubes again had higher lumen output and lumen maintenance than the lamps with the conventional quartz arc tubes~ These results are con~istent with the results of the first test shown in Figs. 2(a) -2(d). Each of these tests indicates that lamps having arc tubes made from ozone free quartz perform significantly better in terms of both lumen output and lumen maintenance than lamps utilizing conventional arc tubes.
While there have been shown and described what are at present considered the preferred embodiments of the present inven~ion, it will be understood by those skilled in the art that various changes and modlfications may be made therein without departing from the scope of the invention as defined ~-~
by the appended claims~
.~
, .. ".. , .. .. ~ ,. ,. ,,, .. j .. , ,.. , ,., ... , ,.. ,, . ~ , . .. . . .. . .. . . .
;"
to the arc tube. The ZrO2 coating prevents W photons from reaching the metal surfaces, thereby preventing any electrons from being e~ected therefrom. In addition to ZrO2, ceramic tubes or other ceramic coatings have also been used to perform this function. ~his technlque of shielding the metal surfaces within the lamp envelope suffers from disadvantages in that it increases the manufacturing costs of the metal halide lamps and may not be durable for extended burn life.
It is known to utilize titanium doped fused quartz to absorb W radiation in reprographic lamps. The reduction of W radiation in these lamps i5 beneficial hecause at some wavelengths, the W radiation produces ozone and at other wavelengths, the W radiation can damage human eyesight.
It is a general object of the present invention to provide improved metal halide arc discharge lamps.
It is a another object of the present invention to provide an improved arc tube for use in a metal halide arc discharge lamp.
It is a further ob~ect of the present invention to provide an arc discharge lamp wherein sodium loss ~rom the arc tube is relatively low. -It is a further obiect of the present invention to provide a metal halide discharge lamp having increased light output.
Summary of the Invention According to the present invention, these and other objects and advantages are achieved in an arc tube for a metal halide lamp comprising an arc tube wall formed of titanium oxide dopPd vitreous silica. The vitreous silica is formed by doping guartz sand with a titanium compound, ~! ". ' . ,-; . . ',',', , . ` -2~
92-1-082 PAT~NT
such as titanium oxide, prior to melting. The concentration of the titanium oxide dopant i in the range of one hundred and fifty to three hundred and fiPty parts per mlllion by weight~ with the preferred concentration being approximately two hundred and fifty parts per million by weight. Metal halide discharge lamps utilizing arc tubes formed from the titanium oxide doped quartz demonstrate increased lumen output and lumen maintenance.
Brief Description of the Drawinq Fig. 1 is an illustrative example of a metal halide discharge lamp;
Figs. 2(a) - 2(d) are graphs of results from a first test comparing the performance of standard production lamps with lamps having arc tubes made of quartz doped with TiO2;
Figs. 3(a) - 3(d) are graphs showing the relative concentrations of various ion species as a function of time for the lamps taken over the course of the first test; and Fig~. 4~a~ ~ 4(d) are graphs of results from a second test comparing the performance of standard production lamps wlth lamps having arc tubes made of quartz doped with TiO2. ~-Detailed Description of the Invention --The present invention is directed to an improved arc -~
tube for use in a metal halide lamp. Fiq. 1 illustrates a typical metal halide arc discharge lamp in which the present invention can be utilized. It should be understood ~hat .
Fig. 1 is provided merely for illustrative purposes and that the arc tube of the present invention can be used with any type of metal halide arc tube lamp, including those having structures that differ from the example shown in Fig. 1. In ~-Fig. 1, a lamp 2 includes a lamp envelope 4 and an arc tube ~
' . .
tû 3 6 mounted within lamp envelope 4. The arc tube 6 is a metal halide arc discharge tube having characteristics that are fully described below.
The arc tube 6 is supported within the envelope 4 via a lower support means 8 and an upper support means 10. Lower support means 8 comprises a U-shaped support made up of vertical wires 14 and 16 extending from a base wire 18. The vertical wires 14 and 16 are welded to a strap 20 tha~
supports the lower end of the arc tube 6. Upper support means 10 similarly comprises a U-shaped support made up of vertical wires 22 and 24 extending from a base wire 26. The vertical wires 22 and 24 are welded to a strap 28 that supports the upper end of the arc tube 6.
Electrical energy is coupled to the arc tube 6 through a base 28. A pair of stiff lead-in wires 30 and 32 are electrically connected to the base 28. Lead-in wire 32 is welded to base wire 18 of the lower support means 8. An additional lead-in wire 34 is electrically connected to vertical wire 16 of lower support means 8. Lead-in wire 34 :~
is connected, via a molybdenum foil 36, to an electrode 38 within the arc tube 6. A resistor 40 is attached to lead-in wire 30 and to a connector 42. Connector 42 is connected, via a molybdenum foil 44, to a starting probe 46.
At the upper end of arc tube 6, a lead-in wire 48 is attached, via a molybdenum foil 50, to an electrode 52. ~:
Lead-in wire 48 is electrically connected to stiff lead-in wire 30 through a thin conducting lead 54. The molybdenum foils 36, 44 and 50 are located in press seals at opposite ends of arc tube 6.
As s~ated above, the present invention is directed to an improved arc tube for use ln a metal halide lamp such as the one shown in F~g. 1. The arc tube of the present invention is formed of a titanium oxide doped vitreous silica. In one embodiment o~ the invention, the vitreous ~ilica i~ fused quartz that is made from a melt doped with TiO2. This doped quartz is hereafter referred to as "ozone free quartz"
because the titanium oxide dopant reduces the emission of W
radiation from the arc tube that would produce ozone. By utilizing ozone free quartz rather than conventional quartz in forming the arc tube/ it is believed that sodium loss from the arc tube is reduced ln two ways. First, the titanium oxide in the ozone free quartz may help to retard the ~ovement of sodium ions through the arc tube wall.
Second, the titanium oxide in the ozone free quartz absorbs~:
W radiation so that the amount of W radiation emitted from the arc tube is reduced. As previously stated, one theory regarding the cau~e of sodium loss in metal halide lamps suggests that W photons emitted from the arc tube cause electrons to be ejected from materials in the outer jacket, thereby generating a negativel~ chaxged layer that attracts positively charged sodium ions through the arc tube wall.
Consequently, by reducing the amount of W radiation emitted from the arc tube, it is believed that the use of ozone free quartz results in a reduction of sodium loss from the arc :-tube of the metal halide discharge lamp. -~
In order to verify the performance of the arc tubes made from ozone free quartz, a series of tests was run comparing--~
four standard production GTE M175U Metalarc lamps (utilizing ::
arc tubes made from quartz that did not contain a TiO2 --~:
dopant), with four GTE M175U Metalarc lamps having arc tubes .
made of ozone free quartz. All the test lamps were made at ~
the same ~ime as part of a single production run. The ozone:`
free quartz was made by doping the quartz sand normally utilized to form metal halide arc tubes with TiO2 prior to ~2~
melting. Thereafter, the mixture o quartz sand and TiO2 was melted and formed into arc tubes in a conventlonal manner that is known to those skilled ln the art.
The concentration of titanium oxide in the ozone free quartz utilized for the test run described above was 250 parts per million by weight. However, it is believed that the advantages of the present invention an be achieved with ozone free quartz having various other concentrations of titanium oxide within the range of 150 to 350 parts per million by weight. Additionally, although TiO2 was used as the dopant in forming the ozone free quartz, other titanium compounds could also be utilized that form titanium oxide when heated. Examples of other titanium compounds that are - ~-believed to be suitable for use as a dopant are titanium nitrate and compounds from the family of titanium alkoxides, such as tetrabutyl titanate. Similarly, although the arc tubes utilized in the test lamps were formed from doped quartz, it should be appreciated that arc tubes embodying the present invention can also be formed from other types of vitreous silica such as synthetic silica produced from silane.
Prior to forming the ozone free quartz into tubes, it was vacuum baked to a low hydroxyl content indicated by a BetaoH of 0.0005 to 0.0007 nm-l. Testing indicated that the amount of W radiation emitted from the ozone free quartz wa~ reduced to approximately zero at wavelengths below approximately 200 nm, with the 50~ W cut-off at approxim~tely 240 nm. This test verifies that the use of ozone free quartz should successfully reduce the W
radiation emitted from~the arc tube. As a result, the amount of photons available for ejecting electrons from materials in the outer jacket ~hould be ~ignificantly i! .;, " ; ~ . , ,. ,.. :, ~ 2 ~ ~ 2 ~
_ g _ .
reduced, thereby reducing sodium loss ln comparison to metal halide lamps having arc tubes formed from conventlonal fused quartz.
Figs. 2(a) - 2(d~ show a compari~on of the results of a first test comparing the performance of the four lamps having ozone free quartz arc tubes (indicated by plots 30, 32, 34 and 36) with the four standard production lamps ~-~
(indicated by plots 31, ~3, 35 and 37). Figs. 2(a)-2(d) are graphs of arc tube voltage, lumen output, color ~emperature and color rendering index, respectively, as a function of time. As can be seen from Fig. 2(b), the lamps having arc tubes made from ozone free quartz (indicated by plot 32) displayed roughly a 20~ improvement in both lumen output and lumen maintenance at 6,000 hours from the standard production lamps (indicated by plok 33). The improvemen~ in lumen output and lumen maintenance indicates that lamps utiiizing ozone free quartz arc tubes have a significant performance advankage over lamps with arc tubes made from ~onventional fused guartz.
The improvement in both lumen output and lumen maintenance was unexpected prior to conducting the above-described te~t~ The reason for the improved lumen output and lumen maintenance exhibited by the arc tubes made from ozone free quartz is not precisely known. It i5 possible that the increased sodium retention resulting from the use of the titanium oxide dopant enables the arc tubes made from ozone free quartz to have greater lumen output over a longer period of time than conventional arc tubes. It is also possible that the tLtanium oxide dopant changes the conductivity of the arc tube, thereby altering khe energy -~
balance in a manner that results in the generation of an increased amount of visible radiation. Additionally, the 92-1-082 2~G6i PA~ENT
-- 1~ --energy balance may also be altered by the conversion of W
radiation into thermal or visible radiation since the titanium oxide dopant inhibits W radiation from escaping the arc tube.
An analysis of Figs. 2(a) - 2(d) demonstrates that the lamps having arc tubes made from ozone free quartz not only -~
demonstrated improved lumen output and lumen maintenance, but also did not demonstrate any significant deficiencies with regard to other lamp characteristics. Although the lamps made with arc tubes of ozone free quartz had a higher voltage ratinq, their voltage reached a plateau at approximately 3,000 hours and thereafter remained steady while the voltage of the standard production lamps continued to rise in an undesirable fashion. The color rendering index (CRI) remained lower for the lamps utilizing the ozone free quartz arc tubes for the majority of the test. The voltage plateau and lower color rendering index for the lamps having ozone free quartz arc t~bes is believed to be thie result of a reduction in sodium loss from those arc tubes.
Figs. 3(a) - 3(d) are graphs showing the relative concentrations of various ion species as a function of time for the lamps having arc tubes made from ozone free quartz (indicated by plots 38, 40, 42 and 44) and the standard production lamps (indicated by plots 39, 41, 43 and 45).
These graphs show no major differences in the arc species contents between the groups, althouqh the iodine content of the ozone free group (indicated by plot 44) hit a plateau early while that of the control group ~indicated by plot 45) gradually dropped. The similarity of values for scandium and sodium in the two groups of lamps suggests that the higher lumen production in the group of lamps with the ozone 92-1-082 - 11 - P~TENT
free quartz arc tubes dld not result from heating of those arc tube~.
Figs. 4(a) - 4(d) illustrate the results of a second lamp test which utilized double ended lamps of a non-standard design. The control group (indicated by plots 47, ~
49, 51 and 53) utilized standard 175W production arc tubes ~-while the test group (indicated by plots 46, 48, 50 and 52) utilized lamps that were made at the same time and were identical except for the use of arc tubes formed from ozone-~-free quartz. Many of the lamps in both groups failed early in the test as a result of oxidation at the inleads of the outer jacket. However, those that survived showed that the lamps with the ozone free arc tubes again had higher lumen output and lumen maintenance than the lamps with the conventional quartz arc tubes~ These results are con~istent with the results of the first test shown in Figs. 2(a) -2(d). Each of these tests indicates that lamps having arc tubes made from ozone free quartz perform significantly better in terms of both lumen output and lumen maintenance than lamps utilizing conventional arc tubes.
While there have been shown and described what are at present considered the preferred embodiments of the present inven~ion, it will be understood by those skilled in the art that various changes and modlfications may be made therein without departing from the scope of the invention as defined ~-~
by the appended claims~
.~
, .. ".. , .. .. ~ ,. ,. ,,, .. j .. , ,.. , ,., ... , ,.. ,, . ~ , . .. . . .. . .. . . .
Claims (20)
1. In a metal halide arc discharge lamp, an arc tube comprising:
a pair of electrodes;
fill material including mercury, metal halide additives and a rare gas; and a sealed arc tube wall enclosing the electrodes and the fill material, said arc tube wall being formed of a titanium oxide doped vitreous silica.
a pair of electrodes;
fill material including mercury, metal halide additives and a rare gas; and a sealed arc tube wall enclosing the electrodes and the fill material, said arc tube wall being formed of a titanium oxide doped vitreous silica.
2. An arc tube as defined in claim 1 wherein the concentration of titanium oxide in the vitreous silica is within the range of about 150 to 350 parts per million by weight.
3. An arc tube as defined in claim 2 wherein the titanium oxide doped vitreous silica comprises fused quartz doped with TiO2.
4. An arc tube as defined in claim 1 wherein the concentration of titanium oxide in the vitreous silica is about 250 parts per million by weight.
5. An arc tube as defined in claim 1 wherein the fill material includes a sodium halide.
6. An arc tube as defined in claim 5 wherein the concentration of titanium oxide in the vitreous silica is within the range of about 150 to 350 parts per million by weight.
7. An arc tube as defined in claim 5 wherein the concentration of titanium oxide in the vitreous silica is about 250 parts per million by weight.
8. An arc tube as defined in claim 5 wherein the the titanium oxide doped vitreous silica comprises fused quartz doped with TiO2 by weight.
9. An arc tube as defined in claim 1 wherein the the titanium doped vitreous silica comprises fused quartz doped with TiO2.
10. A metal halide arc discharge lamp, comprising:
a lamp envelope;
an arc tube assembly supported within said lamp envelope, said arc tube assembly including;
a pair of electrodes;
a fill material including mercury, metal halide additives and a rare gas; and a sealed arc tube enclosing the electrodes and the fill material, said arc tube being formed of titanium oxide doped vitreous silica; and means for coupling electrical energy through the lamp envelope and the arc tube to said electrodes.
a lamp envelope;
an arc tube assembly supported within said lamp envelope, said arc tube assembly including;
a pair of electrodes;
a fill material including mercury, metal halide additives and a rare gas; and a sealed arc tube enclosing the electrodes and the fill material, said arc tube being formed of titanium oxide doped vitreous silica; and means for coupling electrical energy through the lamp envelope and the arc tube to said electrodes.
11. A metal halide discharge lamp as defined in claim 10 wherein the the titanium oxide doped vitreous silica comprises fused quartz doped with TiO2.
12. A metal halide discharge lamp as defined in claim 10 wherein the concentration of titanium oxide in the vitreous silica is within the range of about 150 to 350 parts per million by weight.
13. A metal halide discharge lamp as defined in claim 12 wherein the the titanium oxide doped vitreous silica comprises fused quartz doped with TiO2.
14. A metal halide discharge lamp as defined in claim 10 wherein the concentration of titanium oxide in the vitreous silica is about 250 parts per million by weight.
15. A metal halide discharge lamp as defined in claim 10 wherein the fill material includes a sodium halide.
16. A metal halide discharge lamp as defined in claim 15 wherein the the titanium oxide doped vitreous silica comprises fused quartz doped with TiO2.
17. A metal halide discharge lamp as defined in claim 15 wherein the concentration of titanium oxide in the vitreous silica is within the range of about 150 to 350 parts per million by weight.
18. A metal halide discharge lamp as defined in claim 15 wherein the concentration of titanium oxide in the vitreous silica is about 250 parts per million by weight.
19. In a metal halide arc discharge lamp, an arc tube comprising:
a pair of electrodes;
a fill material including mercury, a sodium halide and a rare gas; and a sealed arc tube wall enclosing the electrodes and the fill material, said arc tube wall being formed of a titanium oxide doped fused quartz, the concentration of titanium oxide in the fused quartz being about 250 parts per million by weight.
a pair of electrodes;
a fill material including mercury, a sodium halide and a rare gas; and a sealed arc tube wall enclosing the electrodes and the fill material, said arc tube wall being formed of a titanium oxide doped fused quartz, the concentration of titanium oxide in the fused quartz being about 250 parts per million by weight.
20. Each and every novel feature or novel combination of features herein disclosed.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US99560392A | 1992-12-22 | 1992-12-22 | |
| US7/995,603 | 1992-12-22 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2112063A1 true CA2112063A1 (en) | 1994-06-23 |
Family
ID=25541994
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2112063 Abandoned CA2112063A1 (en) | 1992-12-22 | 1993-12-21 | Metal halide lamp |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0604207B1 (en) |
| CA (1) | CA2112063A1 (en) |
| DE (1) | DE69328857T2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP3916887B2 (en) * | 2001-06-05 | 2007-05-23 | 株式会社小糸製作所 | Lighting device |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3148300A (en) * | 1961-08-04 | 1964-09-08 | Gen Electric | Lamp having envelope of glass opaque to ultraviolet radiation |
| US3988628A (en) * | 1974-06-13 | 1976-10-26 | General Electric Company | Metal halide lamp with titania-silicate barrier zone in fused silica envelope |
| FR2599890B1 (en) * | 1986-06-09 | 1990-02-02 | Ushio Electric Inc | FUSED SILICA ENCLOSURE FOR DISCHARGE LAMP |
| US5196759B1 (en) * | 1992-02-28 | 1996-09-24 | Gen Electric | High temperature lamps having UV absorbing quartz envelope |
-
1993
- 1993-12-21 CA CA 2112063 patent/CA2112063A1/en not_active Abandoned
- 1993-12-22 EP EP19930310407 patent/EP0604207B1/en not_active Expired - Lifetime
- 1993-12-22 DE DE1993628857 patent/DE69328857T2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0604207B1 (en) | 2000-06-14 |
| DE69328857D1 (en) | 2000-07-20 |
| EP0604207A1 (en) | 1994-06-29 |
| DE69328857T2 (en) | 2001-02-22 |
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