EP0041721B1 - High pressure sodium lamp having improved efficacy - Google Patents

High pressure sodium lamp having improved efficacy Download PDF

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Publication number
EP0041721B1
EP0041721B1 EP19810104390 EP81104390A EP0041721B1 EP 0041721 B1 EP0041721 B1 EP 0041721B1 EP 19810104390 EP19810104390 EP 19810104390 EP 81104390 A EP81104390 A EP 81104390A EP 0041721 B1 EP0041721 B1 EP 0041721B1
Authority
EP
European Patent Office
Prior art keywords
arc
lamp
sodium
arc tube
wall
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.)
Expired
Application number
EP19810104390
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0041721A2 (en
EP0041721A3 (en
Inventor
John F. Waymouth
Elliot F. Wyner
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Osram Sylvania Inc
Original Assignee
GTE Products Corp
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by GTE Products Corp filed Critical GTE Products Corp
Publication of EP0041721A2 publication Critical patent/EP0041721A2/en
Publication of EP0041721A3 publication Critical patent/EP0041721A3/en
Application granted granted Critical
Publication of EP0041721B1 publication Critical patent/EP0041721B1/en
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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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/82—Lamps with high-pressure unconstricted discharge having a cold pressure > 400 Torr
    • H01J61/825—High-pressure sodium lamps

Definitions

  • This invention is concerned with high efficacy high pressure sodium (HPS) arc discharge lamps as disclosed e.g. in US-A-39 06 272.
  • HPS high pressure sodium
  • Such lamps have a non-vitreous, for example alumina, art tube having electrodes at its ends and containing sodium, mercury, and a starting gas.
  • the invention is particularly concerned with improving the efficacy of such lamps by design changes which reduce the wall loading, and reduce the average arc current density while simultaneously maintaining the wall temperature above about 1100°C.
  • Figure 2 illustrates the measured dependence of efficacy as a function of arc tube wall temperature determined from an experiment in which the wall temperature of a lightly-loaded arc tube was varied by operating it inside an independently controllable furnace.
  • arc temperatures which result from such conditions of operation are typically of the order of 4000K, and increase with increasing power per unit length.
  • the dependencies on arc temperature of two of the major useless radiative energy-loss mechanisms of the arc are substantially greater than that of the useful visible emission in the sodium D lines. Accordingly, as arc temperature increases, these two useless energy loss mechanisms increase faster than the desired sodium D emission, decreasing the ratio of useful visible to non-useful infrared, and with it the efficacy.
  • efficacy would decrease with increasing power per unit length, and therefore wall loading.
  • efficacy would increase as the power per unit length and the arc temperature decrease.
  • Figure 3 is a plot of efficacy (normalized to that of the prior art 400 watt lamp, 0.7 cm in inside diameter) vs power input per unit length, with tube diameter as a parameter; constant wall temperature and optimum sodium pressure for each diameter is assumed.
  • the change in the shape of radial temperature profile of the arc with diameter is neglected; when this factor is included in a more detailed calculation, the increase of efficacy with diameter is not quite as large, but the trend is identical.
  • the existence of a maximum in efficacy at an optimum power per unit length is clearly visible in these calculations; the optimum power per unit length appears to be in the vicinity of 20 to 25 watts/cm, substantially below the values of many prior art lamps.
  • the lamp includes means to maintain the arc tube wall temperature greater than about 1100°C at the central section, and to maintain the temperature of the sodium-mercury amalgam reservoir at the value yielding optimum sodium vapor pressure, and that during normal operation the wall loading is less than about 13 W/cm 2 of arc tube external wall surface, and the current density is less than about 8 Alcm 2 of arc tube internal cross sectional area.
  • the operating wall temperature may be increased by improved thermal insulation of the arc tube or by a reduction in primary thermal radiation and/or heat conduction of the arc tube material.
  • Means should be provided to maintain the sodium-mercury amalgam reservoir temperature at the value yield optimum sodium vapor pressure.
  • thermally insulating the arc tube are disposed within or upon the inner surface of said outer jacket.
  • said thermally insulating means is an infrared reflective coating of indium oxide and tin oxide, and preferably such a reflective coating is disposed on the inner surface of a sleeve surrounding the arc tube within said outer jacket.
  • the means for increasing the operating wall temperature are utilized to make feasible the employment of arc tubes of substantially larger diameter than prior art arc tubes, in order to achieve the efficacy gain associated with said larger diameter by keeping the wall temperature at or near the maximum permitted by the material (about 1500K for polycrystalline alumina) in spite of the reduced wall loading.
  • Prior art arc tubes had arc tube outer diameters of about 0.6 to 1.0 cm and operated (when optimally designed) at wall loadings of about 14 to 20 watts/cm2.
  • Prior art arc tubes also generally operated at about 25 to 50 watts per cm of arc length; in this invention, the power consumption per cm of arc length is generally less.
  • Example 1 illustrates the comparison between the performance of a prior art lamp and that of a lamp constructed in accordance with the teachings of this invention, employing translucent polycrystalline yttrium oxide (yttria) as the arc tube material instead of alumina.
  • yttria translucent polycrystalline yttrium oxide
  • Both translucent ceramics have the property of becoming opaque in the infrared spectral region.
  • Alumina becomes absorbent between about 4 microns and about 7 microns wavelength
  • yttria becomes absorbent between about 7 microns and about 9 microns; thus yttria will intrinsically thermally radiate less than alumina at temperatures about 1200°C.
  • the thermal radiant emittances of translucent polycrystalline yttria arc tubes have been measured to be about 0.11, while those of polycrystalline alumina are typically 0.20. This permits the yttria arc tube to reach a higher wall temperature for a given power per unit area dissipation or, more importantly for our purposes, to achieve equal temperature to an alumina arc tube wall at a lower power per unit area.
  • a higher efficacy lamp by means of a larger diameter, lower-wall-loaded yttria arc tube maintained at equal or nearly equal temperature as an arc tube designed according to the prior art.
  • Example 2 shows the results for a 150 watt 55 volt HPS lamp made in accordance with this invention as compared to a 150 watt 55 volt HPS prior art lamp.
  • the lamp as per this invention had an 8 mm inside diameter yttria arc tube while the prior art lamp had a 5.87 mm inside diameter alumina arc tube, which is very close to the diameter of 5.75 mm disclosed in US-A-3 906 272 to be optimum for this lamp.
  • Example 3 shows the comparison in efficacy between a 50 watt lamp according to our invention employing an yttria arc tube for reduced thermal radiative losses, and two different versions, A and B of 50 watt prior art lamps.
  • Prior art lamp A has been manufactured for only about a year and has been known to not have been optimized according to the known prior art, by virtue of its very low wall loading and low arc tube wall temperature.
  • Experimental lamps manufactured according to our invention with yttria arc tubes of identical dimension have substantially increased arc tube wall temperatures and correspondingly increased efficacy.
  • Recently announced prior art lamp B represents an attempt to further optimize the 50 watt lamp according to the known prior art principles, viz., by decreasing the arc tube diameter, shortening the arc length, increasing the wall loading.
  • Optimum diameter for this lamp according to US-A-3 906 272 is 0.335 cm. It should be noted that despite a deviation of more than 40% from said optimum diameter, the lamp according to our invention has equivalent efficacy. Moreover, prior art Lamp A was deliberately designed at less than optimum wall loading for alumina in order to improve its lumen maintenance and ease of manufacture, advantages which are retained by our lamp but are lost in the more recent prior art lamp B.
  • a conventional 400 watt lamp was constructed with an alumina arc tube, 7.3 mm inner diameter by 8.9 mm outer diameter, inside the usual type 7720 glass outer jacket.
  • a quartz sleeve 29 mm inner diameter by 33 mm outer diameter, surrounded the arc tube within the outer jacket.
  • On the inner surface of the quartz sleeve was an infrared reflective coating of indium oxide and tin oxide. Lamp operation is summarized below.
  • the wall temperature is higher than 1200°C normally associated with the conventional 7.3 mm I.D. design.
  • the quartz sleeve will permit the use of larger diameter on tubes.
  • the use of such a sleeve provides two additional glass interferences which the light emitted by the arc tube has to pass through. A large percentage of the reflected radiation from the glass interferences is then lost through absorption within the lamp. If the observed efficacy of about 124 LPW is corrected for this loss, we see that the efficacy of the arc tube has increased substantially above that of the same arc tube mounted without heat conserving means, and is in fact, substantially greater than the 125 LPW obtainable from prior art 400 watt lamps. This increase in efficacy has resulted from the reduction in self-absorption of the sodium D radiation brought about by the lower sodium atom density near the wall that is a consequence of the higher wall temperature.
  • Example 5 we describe the application of the radiant-reflector principle of thermal insulation to an arc tube with a larger diameter.
  • a lamp (Lamp C) was made comprising a large diameter alumina arc tube, 11.0 mm I.D. by 12.5 mm O.D. within a cylindrical type 7720 glass outer jacket. There was an infrared reflective coating, similar to that of Example 4, on the inner surface of the jacket. Performance of Lamp C was compared with that of a similar lamp (Lamp D) without the infrared reflective coating (but with niobium heat shields at the arc tube ends to raise the end temperature, therefore the pressure, of the sodium-mercury amalgam). Performance of the lamps is summarized below.
  • the 250 watt lamp has a wall loading of 14.6 watts/cm2, an ID of 0.732 cm and delivers about 26500 lumens, while the 250S lamp has a wall loading of 19.44 watts/cm2, an ID of 0.587 cm and delivers about 29000 lumens.
  • the optimum diameter for this lamp is approximately 0.55 cm.
  • the lamps in Table I are typically designed for maximum efficacy according to the teachings of the prior art. None of the lamps are designed with a diameter large enough that the current density is as low as 8.0 amp/cm 2 . Nor are any of the lamps designed with a wall loading as low as 13 watts/cm2. Moreover, the efficacies indicated appear generally to increase with increasing wall temperature, and all wall temperatures appear to be in excess of about 1100°C. Thus, we may conclude that the optimum diameters cited in US-A-3 906 272 for each lamp simply represent the largest possible diameter consistent with a minimum wall temperature of 1100°C for conventionally constructed high pressure sodium lamps.
  • the central concept of our invention is that still higher efficacies can be obtained at still larger diameters when suitable steps are taken to reduce the thermal radiative losses from the arc tube surface so that its temperature can be maintained above 1100°C even though the heat energy input per unit area of wall surface may be reduced.
  • a lamp in accordance with this invention comprises a non-vitreous arc tube 1 having electrodes 2 sealed into the ends.
  • Arc tube 1 contains sodium, mercury and a starting gas, typically, xenon.
  • a metal framework 3 provides support for the arc tube and an electrical path to the upper electrode.
  • a support wire 4 is embedded in glass press 5 and provides electrical connection to the lower electrode.
  • the arc tube assembly is contained within an outer glass jacket 6.
  • Arc tube 1 was made of yttria and the results for a 150 watt lamp and a 400 watt lamp made in accordance therewith are shown in Examples 2 and 1 above, respectively.

Landscapes

  • Discharge Lamps And Accessories Thereof (AREA)
  • Vessels And Coating Films For Discharge Lamps (AREA)
  • Discharge Lamp (AREA)
EP19810104390 1980-06-06 1981-06-06 High pressure sodium lamp having improved efficacy Expired EP0041721B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US15699680A 1980-06-06 1980-06-06
US156996 1998-09-18

Publications (3)

Publication Number Publication Date
EP0041721A2 EP0041721A2 (en) 1981-12-16
EP0041721A3 EP0041721A3 (en) 1982-09-15
EP0041721B1 true EP0041721B1 (en) 1985-04-17

Family

ID=22561939

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19810104390 Expired EP0041721B1 (en) 1980-06-06 1981-06-06 High pressure sodium lamp having improved efficacy

Country Status (4)

Country Link
EP (1) EP0041721B1 (enrdf_load_stackoverflow)
JP (1) JPH0211717Y2 (enrdf_load_stackoverflow)
CA (1) CA1203559A (enrdf_load_stackoverflow)
DE (1) DE3169958D1 (enrdf_load_stackoverflow)

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1266181A (fr) * 1960-08-26 1961-07-07 Lampes Sa Lampes à décharge à enveloppe en alumine transparente
JPS5710543B2 (enrdf_load_stackoverflow) * 1972-03-16 1982-02-26
US3906272A (en) * 1974-04-01 1975-09-16 Gen Electric Low wattage high pressure sodium vapor lamps
GB1597162A (en) * 1977-03-10 1981-09-03 Ngk Insulators Ltd Transparent polycrystalline alumina and high pressure vapour discharge lamp

Also Published As

Publication number Publication date
EP0041721A2 (en) 1981-12-16
DE3169958D1 (en) 1985-05-23
JPH0211717Y2 (enrdf_load_stackoverflow) 1990-03-28
EP0041721A3 (en) 1982-09-15
JPS572567U (enrdf_load_stackoverflow) 1982-01-07
CA1203559A (en) 1986-04-22

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