FR2541043A1 - HIGH PRESSURE SODIUM VAPOR LAMP HAVING AN OXYGEN GETTER - Google Patents

Abstract

HIGH PRESSURE SODIUM STEAM LAMP WITH OXYGEN GETTER FOR AN IMPROVED COLOR RENDERING. IT INCLUDES: -A GLASS EXTERIOR ENVELOPE 12; -A ARC TUBE 19 CONTAINED INSIDE THE EXTERIOR ENCLOSURE 12 AND IN WHICH IS SEALED A PAIR OF THERMOIONIC ELECTRODES STRUCTURE 44, 46, 48, 50, THIS TUBE A ARC CONTAINING A LOAD OF VAPORIZABLE METAL WITH A PARTIAL SODIUM PRESSURE BETWEEN APPROXIMATELY 100 AND 400 TORRS AND XENON GAS AT A PRESSURE BETWEEN 10 AND 400 TORRS, AND A GETTER OF OXYGEN 40 FIXED TO AT LEAST ONE OF THE ELECTRODES STRUCTURES THERMOIONICS OF THIS ARC TUBE, THIS OXYGEN GETTER CONSISTING OF A METAL CHOSEN FROM THE GROUP OF ZIRCONIUM, VANADIUM, TITANIUM, YTTRIUM AND THORIUM AND THEIR ALLOYS EXCLUDING THOSE OF YTTRIUM. APPLICATION TO HIGH PRESSURE METAL LAMPS.

Description

The present invention relates to a steam lamp

  of high pressure sodium comprising an integral envelope

  Alumina ceramic lamp, and more particularly, a high-pressure sodium vapor lamp in which an inner arc tube is provided with a pair of electro-thermal electrodes to at least one of which is fixed an oxygen getter which maintain color rendering

of the lamp.

  High pressure sodium lamps have found wide use during the last decade

  for commercial lighting applications, especially

  outdoor lighting These lamps are described

  in U.S. Patent No. 3,248,590.

  High-pressure sodium lamps typically comprise an elongated tubular inner shell made of refractory oxide transmitting light resistant to

  sodium at high temperatures, and suitably formed

  High density polycrystalline alumina material The ceramic arc tube is generally supported in a glassy outer casing or bulb provided at one end of a conventional screw cap. The electrodes of the inner casing are connected to terminals of the cap, that is to say the central contact and the contact of the shell of this cap The space between the inner and outer envelopes is usually under vacuum so

to keep the heat.

  The color rendering of standard high-pressure sodium lamps can be improved by increasing the partial pressure of sodium in the arc chamber of

  the inner envelope formed of polycrystalline alumina.

  An improved color rendering of standard high-pressure sodium lamps may require that the polycrystalline alumina arc chamber operate with two to three times the internal sodium partial pressure as compared to conventional standard lamps. increased sodium, the wall temperature between the electrode tips in the arc chamber can be increased by 1000 C compared to the standard lamp so

  to correct the reduction in luminous efficiency which

  loin normally operating at a pressure of

increased sodium.

  High pressure sodium vapor lamps have conventionally been developed by increasing the operating temperature of the sodium amalgam tank typically located at one of the thermionic electrodes within the arc tube and thermally connected thereto. this is well known in the art of high pressure sodium lamps, at pressures in the arc tube two to three times higher than arc tubes of high pressure sodium lamps of standard color, the extra pressure expands

  the line of resonance of sodium and radiation

  tinus at the wavelengths of blue and green, which

  actually increases the color temperature correlated

  of several hundred degrees Kelvin, and the color rendering index of the high-pressure sodium vapor lamp is thus desirably increased

  up to a range of between 6 00 and 85.

  Arc tubes of improved high pressure sodium vapor lamps may be the seat of undesirable sodium losses caused by chemical reactions of oxygen sources in the arc tube created by

  impurities introduced into the arc tube during the

  manufacture of improved sodium vapor lamps

  These undesirable impurities act, typically undesirably, on the performance of the lamp as evidenced by increased arc tube voltage, reduced light efficiency of the high pressure sodium lamp, color shift towards the lamp. the red part of the electromagnetic spectrum visible during the life of the lamp This displacement of color towards the red is particularly troublesome when the lamp of high-pressure sodium vapor is used in

  commercial and industrial applications for

  In addition, it has been empirically determined that color high-pressure sodium vapor lamps exhibit a greater color shift, mainly related to the red spectral content than the standard lamp for the same amount of sodium loss due to color. the

internal chemical reactions.

  U.S. Patent No. 3,485,343 discloses undesirable chemical reactions related to the high-pressure sodium vapor arc lamp tube. This patent describes the reaction of sodium with small amounts of oxygen and water. may be present in an arc tube, which in turn favors the reaction

  with the alumina of the arc tube resulting in an elimination of

  This patent further discloses the use of an oxygen getter formed by doping a metal with about 2 to 20% by weight of a metal cation having a plus four valence such as 90% yttrium alloy, 10%

  thorium This oxygen getter based on yttrium alloy

  thorium is a relatively expensive material It would be desirable to find an oxygen getter that is a relatively inexpensive material so that the undesirable chemical reactions that affect the rendering of

  desired color can be eliminated in a

inexpensive.

  Accordingly, it is an object of the present invention to provide a means for improving the color rendition of high pressure sodium vapor lamps so that the color shift thereof typically caused by undesirable chemical reactions between the dose of sodium and oxygen sources contained non-

  desirable in the arc tube thus reduced.

  It is also intended to provide means for reducing the undesirable chemical reactions of an improved high pressure sodium vapor lamp,

  such that the color rendering index remains practically

  only constant during the life of the lamp.

  The present invention relates to improved color rendering high pressure sodium lamps having an oxygen getter to reduce sodium losses.

  typically created in the arc tubes of these lamps.

  Accordingly, according to one embodiment of the present invention, there is provided an improved color rendering high pressure metal vapor lamp comprising an outer glass envelope and an arc tube contained in this outer shell. A pair of thermionic electrodes is sealed to the tube. Arc The arc tube

  contains a vaporizable metal charge having a

  sodium partial pressure between 100 and 400 torr and xenon gas at a pressure between

  and 400 torr The tube further comprises an oxy-getter

  which gene is attached to at least one of the thermo-j electrodes.

  ionic The oxygen getter is a metal selected from the group of zirconium, vanadium, titanium, yttrium, and thorium

  and their alloys except those of yttrium.

  The following description refers to the figures

  annexed which respectively represent: FIG. 1, a front view of a discharge lamp

  high pressure sodium vapor according to the present invention.

  tion; Figure 2 is a slightly enlarged sectional view of the arc tube of Figure 1 in accordance with one embodiment of the present invention; Figure 3 is a slightly enlarged sectional view of the arc tube of Figure 1 showing another embodiment of the present invention;

  Figure 4, a high pressure sodium vapor lamp

  partially broken away to show the two-wire arc tube; Figure 5 is a sectional view of the arc tube of the high-pressure sodium vapor lamp of Figure 4; and, Figure 6, a chromaticity diagram of the International Commission on Illumination showing a typical improvement of the color temperature of the high-pressure sodium vapor lamp produced by the

present invention.

  FIG. 1 shows a high-pressure sodium vapor lamp incorporating the present invention and corresponding to a conventional lamp of 250

  watts A high pressure sodium vapor lamp

  generally takes a vitreous outer casing 12 which, with a standard screw cap Goliath 13, fixed to the end of the rod is shown in the upper part of Figure 1 A reentrant pinch 14 supports a pair of current leads relatively

  15 and 16, passing through the rod 14 and having the ends

  external tees connected to the screwdriver shell 17 and

eyelets 18 from the base.

  The lamp 10 has an inner envelope or

  arc tube 19 located centrally in the outer casing

  The arc tube 19 consists of a long light-transmitting ceramic made of polycrystalline alumina ceramide which is translucent. The arc tube 19 contains a charge of vaporizable metals having a sodium partial pressure of between about 100 and 400. torrs and xenon gas at a pressure of

between 10 and 400 torr.

  The upper end of the arc tube 19 is closed by an alumina ceramic sealing plug 20 through which a niobium conductor 21 which supports an upper electrode (shown more clearly in FIGS. we will describe) in the arc tube 19 Similarly, the end

  lower part of the arc tube 19 has a closure that matches

  A ceramic sealing plug 22 through which a thin-walled niobium tube passes 23 Ceramic sealing plugs 20 and 22 are described in detail in U.S. Patent No. 4,065,691. The niobium tube 23 sett at a time from

  supply conductor for the arc tube 19 and

  storage tank for the alkali metal and excess mercury contained in the arc tube 19 The lower electrode rod (shown in FIGS. 2 and 3) of the arc tube 19 protrudes into the tube 23 of the tank and is fixed in place by crimping the niobium tube of the tank around the lower electrode at the place

  24, as shown in Figure 1.

  The arc tube 19 of the sodium vapor lamp

  10 of FIG. 1 and a two-dimensional arc tube

  62 of the high-pressure sodium vapor lamp 60 of FIG. 4, which will be described hereinafter, are of great interest with respect to the present invention. More particularly, for an embodiment of the present invention. the arrangement of the oxygen getters and 42 around the electrode rods 48 and 50 contained in the arc tube 19 is of particular interest to the present invention and such an arrangement is shown

in Figure 2.

  Figure 2 is a sectional view, slightly enlarged

  The electrodes 44 and 46 each comprise an emissive material with a low working function such as calcium dibarium and calcium tungstate.

  which is formed in the windings wound around the ti-

  electrode gages 48 and 50 respectively.

  Figure 2 further shows the oxygen getters 40 and 42 of the present invention as being wound around the electrode rods 48 and 50, respectively. Although Figure 2 shows each of the electrode rods 48 and 50 as having getters. of oxygen 40 and 42, it should be noted

  that, in accordance with the implementation of the invention, only

  a 40 and 42 oxygen getter is needed with

  one or the other of the electrodes 44 or 46.

  The oxygen getters 40 and 42 are preferably formed solely of zirconium, although other metals such as vanadium, titanium, yttrium or thorium are also usable In addition, these oxygen getters 40 and

  42 can also be an alloy formed from a combination of

  of zirconium, vanadium, titanium and thorium.

  oxygen streams 40 and 42, formed from the selected metals, react with

  chemically with the sources of oxygen gas during the operation of the lamp to prevent a reaction

  oxygen with sodium in the sodium amalgam.

  The oxygen getters 40 and 42 are shown in FIG. 2 in the form of a wire wound around the rods

  48 and 50 The oxygen getters 40 and 42 can

  Alternatively, they may be placed around the electrode rods 48 and 50, respectively, in the form of a sheet. A second embodiment of the present invention is shown in FIG. 3. FIG. 3 is similar to FIG. 2 and uses the same reference numerals as much as possible. The difference between FIG. 2 and FIG. 3 is that the relative oxygen getter to the electrode rod 50 is located in the niobium reservoir tube 23 and has the reference numeral 52 as shown in FIG. 3 although this has not been shown in FIG.

  FIG. 3, the implementation of the present invention

  face the placement of an oxygen getter in the tube

  niobium reservoir 23 and on each of the electrodes rods.

  The oxygen getter 52 may be inserted into the niobium reservoir tube 23 as a wire or

of a rolled sheet.

  Another embodiment of the present invention is a double-coil inner arc tube 62 located in the center of the sodium vapor lamp 60 of FIG. 4 and supported, in part, by a support member 63 The double arc tube coil 62 is shown by means of a partial view of the high-pressure sodium vapor lamp 60 of FIG. 4 The high-pressure sodium vapor lamp 60 is of the LU 35 or LU 50 type commercially available from the General Electric Company. The double-wire arc tube 62 is shown more clearly at

figure 5.

  Figure 5 shows the arc tube 62, preferably

  formed of polycrystalline alumina, as having two

  supply leads 64, 78 located opposite each other,

formed of niobium wire.

  The supply conductor 78 passes through and is supported by the sealing plug 80. The inner part of the conductor 78, marked 82, is connected to a rod 86 by an end weld 84. The inner portion 82 of the conductor 78 constitutes a niobium feedthrough The rod 86 is formed of tungsten and has electrode coils 88 between the turns of which there is an emissive mixture. The emissive mixture can be

  dibaryum tungstate and calcium.

  The input lead 64 passes through and is supported by a ceramic seal plug 66. The inner portion of the lead wire 64, referenced 68, is connected to a rod 72 by an end seal 70. Provided 64 constitutes a niobium feedthrough for the arc tube.

  is formed of tungsten and has electrical windings

  trode 64 similar to electrode coils 88.

  FIG. 5 represents an oxygen spinner 76 wound around the passage of niobium 68 and the rod 72. Although this is not shown in FIG. 5, it is also possible to wind an oxygen getter around the crossing of the niobium 82. and the rod 86, both of which are connected to the niobium feed conductor 78 The oxygen getter 76 is of the same metal as previously described for the getters

oxygen 40, 42 and 52.

  In order to better appreciate the present invention, reference will now be made to comparative test data obtained between high pressure sodium vapor lamps.

  having an improved but degrading color rendering

  and the high pressure sodium lamp of FIG. 4 having the double-wire arc tube 62 of FIG. 5 of the present invention which has an improved color rendering maintained by the oxygen getters of the present invention.

present invention.

  A total of 20 high-watt, 35 watt high-pressure sodium-arc tubes of the double-wire design were constructed and tested in accordance with the practice of this invention.

  high-pressure sodium lamps had a di-

  inner meter of 4.5 mm and an arc interval, that is,

  ie, the space between the thermionic electrodes, 12.0 mm. The 35-watt high-pressure sodium-arc tubes with improved color were dosed with 10 milligrams of amalgam at 25% by weight of sodium, a gas The thermionic electrodes of the arc tubes were activated with a dibaryum and calcium tungstate to improve the thermionic emission of the electrodes. high-pressure sodium vapor was divided into 12 lamps to

  high pressure sodium vapor 60 according to the present invention.

  This invention has oxygen getters 76 and 8 high pressure sodium vapor lamps that do not have oxygen getters. Two of the oxygen getters 76 for each of the high-pressure sodium vapor lamps 60 of the present invention were formed by a single turn of 2.05 mm zirconium wire and each oxygen getter 76 was wound around the base of each electrode rod in a manner similar to that shown in FIG.

  the oxygen getter 76 and located between the electrical windings

  Trodes 74 and 88 and the ceramic end cap 66 and 80 The group of 12 arc tubes 62 of the present invention and the group of 8 arc tubes not having the advantages of the present invention have been placed in

  finished lamps and then subjected to photometric tests.

  All the finished lamps had an initial correlated color temperature of about 22,000 K and an index of

color rendering of 75.

  All lamps were operated for a total of 500 hours at an operating power of 35 watts The results of this operation for 500 hours of the high pressure sodium lamps

  are better described with reference to FIG.

  Figure 6 is a part of the chromatic diagram.

  of the International Commission on Illumination, well known in the art of high pressure sodium vapor lamps The X axis shown in Figure 6 with positions of 0.490, 0.500, 0.510, 0.520 and 0.530, and the Y axis of Figure 6 with positions 0.400, 0.410, 0.420, 0.430 and 0.440, form a coordinate system by means of which variations of the correlated color temperature of lamps during a period can be

  Figure 6 shows a curve 90 representing

  of an ideal black body as it is practically

  obtainable from an incandescent light source.

  Figure 6 shows the curve of the blackbody 90 cut by a set of correlated color temperature curves of 20000 K, 20650 K, 2200 K, 22300 K, 24000 K, and 2600 K. The 20 sodium vapor lamps Jhaute pressure before

  to be tested at 500 hours had a temperature of

  initial correlated color pattern of about 2200K, a color rendering index of 75 and a position 92 shown in Figure 6 Position 92 of Figure 6 is located along the correlated color temperature curve 22000K and at a position just below but

  very close to the curve of the ideal black body 90.

  After subjecting the 20 lamps to the 500-hour test, the 12 lamps 60 improved color rendering

  of the present invention have proved to be advantageous

  advantageously shifted from the correlated color temperature position 92 to a correlated color temperature position 94, and vice versa, the improved color high pressure sodium vapor lamps do not have the oxygen getter 76 of the present invention. turned out to have an unwanted shift down the

  correlated color temperature position 92 to the posi-

  Figure 96, both in Figure 6 This undesirable shift of high pressure sodium lamps not having the advantages of the present invention, is to the red portion of the visible electromagnetic spectrum.

  and conversely, the desirable offset of

  The high pressure sodium scare of the present invention is far from the red part of the visible electromagnetic spectrum.

  high pressure sodium of the present invention is

  in broken lines, in FIG.

  arrow 98 and, similarly, the undesired shift

  table of high-pressure sodium lamps that do not

  are not in agreement with the present invention is

  in broken lines, in FIG.

arrow 100.

  All of the lamps 60 of the present invention and the lamps not having the present invention were physically examined after this 500 hour test. The lamps 60 of the present invention had arc chamber ends which were noticeably cleaner. that the blackened ends of the steam lamps

  high pressure sodium which did not incorporate the

  In particular, the ends are cleaner

  arc chambers of the arc tube 62 of the present invention;

  are beneficial for the efficiency and maintenance of high-pressure sodium lamps

60.

  It will now be noted that the implementation of

  This invention provides improved color high pressure sodium vapor lamps 60 and 10 having a

  improved maintenance of the high color temperature.

  The improvement in maintaining the high color temperature is achieved by the oxygen getter of the present

  It should be noted that although the comparative data

  the 35-watt high-pressure sodium lamps, the present invention contemplates

  also sodium vapor lamps with

  much higher levels such as 1000 watts and conversely much lower powers such

than 15 watts.

Claims (4)

  A high pressure metal vapor lamp having improved color rendering comprising: a vitreous outer shell (12); an arc tube (19) contained within the outer shell (12) and in which is sealed a pair of thermionic electrode structures (44, 46, 48, 50), said arc tube containing a vaporizable metal charge having a sodium partial pressure of between about 100 and 400 torr and xenon gas at a pressure of between 400 and 400 torr, and an oxygen getter (40) attached to at least one of the electrode structures thermoionics of this arc tube, this oxygen getter consisting of a metal selected from the group of zirconium, vanadium, titanium, yttrium and thorium,   and their alloys except those of yttrium.   2 lamp according to claim 1, characterized in that the pair of thermionic electrode structures (48, 50) is connected to a tube (23) serving as a reservoir for storing the excess alkali metal contained in this arc tube and the lamp has disposed inside another oxygen getter (42) of a metal selected from the same group of   metals and alloys as the first oxygen getter men-   tioned. 3 lamp according to claim 1, characterized   in that it further comprises an additional oxygen getter   (52) attached to the other thermocouple electrode structure.   (50) of this arc tube, this additional oxygen getter   (52) being of a metal selected from the same group of   metals and alloys as the first oxygen getter men- tioned.   4 Lamp according to Claim 2, characterized   in that it further comprises an additional oxygen getter   attached to the other thermionic electrode structure of this arc tube, this additional oxygen getter being   in a metal selected from the same group of metals and alloys   only the first oxygen getter mentioned.   Lamp according to claim 1, characterized in   what the thermionic electrode structures have   in addition, a niobium feed conductor (78, 82, 64, 68) extending into said arc tube and provided for   external connections to this arc tube, the other electrical structure   thermionic trode of this arc tube having attached thereto another oxygen getter (76) of a metal selected from the same group of alloying metals as the first oxygen getter mentionned.