EP0506182B1 - High pressure gas discharge lamps - Google Patents

High pressure gas discharge lamps Download PDF

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Publication number
EP0506182B1
EP0506182B1 EP19920200786 EP92200786A EP0506182B1 EP 0506182 B1 EP0506182 B1 EP 0506182B1 EP 19920200786 EP19920200786 EP 19920200786 EP 92200786 A EP92200786 A EP 92200786A EP 0506182 B1 EP0506182 B1 EP 0506182B1
Authority
EP
European Patent Office
Prior art keywords
lamp
coating
arc tube
high pressure
gas discharge
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 - Lifetime
Application number
EP19920200786
Other languages
German (de)
English (en)
French (fr)
Other versions
EP0506182A2 (en
EP0506182A3 (en
Inventor
Raghu Ramaiah
Suzette Kimmel
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.)
Koninklijke Philips NV
Original Assignee
Koninklijke Philips Electronics NV
Philips Electronics NV
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 Koninklijke Philips Electronics NV, Philips Electronics NV filed Critical Koninklijke Philips Electronics NV
Publication of EP0506182A2 publication Critical patent/EP0506182A2/en
Publication of EP0506182A3 publication Critical patent/EP0506182A3/en
Application granted granted Critical
Publication of EP0506182B1 publication Critical patent/EP0506182B1/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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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
    • H01J61/24—Means for obtaining or maintaining the desired pressure within the vessel
    • 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
    • H01J61/35—Vessels; Containers provided with coatings on the walls thereof; Selection of materials for the coatings
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/02—Details
    • H01J61/52—Cooling arrangements; Heating arrangements; Means for circulating gas or vapour within the discharge space
    • H01J61/523—Heating or cooling particular parts of the lamp

Definitions

  • This invention relates to a high pressure gas discharge lamp and particularly to a high pressure sodium vapor lamp, comprising an arc tube; first and second electrodes disposed in said arc tube; vaporizable materials disposed within said tube, which during operation provide a vapor through which current will flow between said electrodes.
  • High Pressure Sodium Lamps exhibit a wide lamp voltage range, regardless of the lamp wattage.
  • This voltage range typically is ⁇ 8 volts for low-voltage lamps, ⁇ 15 volts for high voltage lamps, and up to ⁇ 35 volts for 1000 W HPS lamps.
  • One of the consequences of this spread in lamp voltage is that during operation, the lamp wattage also has a corresponding spread.
  • this voltage spread also represents aspects of spread of lamp manufacturing. Therefore, a method of reduction of the voltage spread is important from lamp quality point of view and thus from manufacturing point of view.
  • Lamp voltage spread in HPS lamps can be ascribed primarily to a single factor (for the purpose of this application we assume that all measurements are made on a reference ballast, thus eliminating the voltage variation due to ballast variations): spread of cold spot or amalgam temperature from lamp to lamp. This is true for the lamp wattages currently in production (the so-called saturated HPS lamps). For each of these lamps it holds that there can always be found in the coldest parts of the operating lamp (called the "cold spot”), a quantity of condensed amalgam of sodium (Na) and Mercury (Hg). The amount (mass) and mole fraction of this amalgam is controlled by the temperature of the cold spot.
  • the temperature of the cold spot controls the vapor pressure of Na and Hg for a given lamp, the dependence of the vapor pressure on cold spot temperature is exponential. Thus minor difference in this temperature have profound effects on the quantities of Na and Hg that may be found in the vapor state.
  • the lamp voltage is primarily dependent on the vapor pressure of these two species. Thus it is evident that the lamp voltage spread is directly related and primarily due to temperature spread of the cold spot between copies of one type of lamp.
  • the spread of cold spot temperature is due to several factors for a given lamp type. Some of the important parameters are: spread and variations in PCA (polycrystalline alumina) arc tube wall thickness, in diameter of the PCA arc tube, in electrode construction (i.e. thermal contact between coil and rod), in composition and distribution of electrode emitter, in scrape height (i.e. the electrodes distance), etc. It is possible that more heat is conducted to the cold spot of the lamp for a thin walled arc-tube than for the thick walled arc-tube. Approximately 38% of the input energy to a HPS lamp is lost by heat conduction through the PCA wall of the arc-tube. During manufacturing of PCA tubes, spread and variations in wall thickness of ⁇ 0.2 mm are typical.
  • the actual value of the cold spot temperature is determined by an energy balance, between conducted heat as input, and primarily radiated power as output. Heat is lost by radiation through emission of infra-red radiation.
  • the spectral emissivity of PCA is 0.2 - 0.3. See in this regard the treatise "The High Pressure Sodium Lamp", de Groot and Van Vliet, Philips Technical Library 1986.
  • the invention has for its object amongst others to provide a measure as to effectively reduce the spread in lamp voltage occurring between individual copies of the lamp as defined in the preamble.
  • a high-pressure discharge lamp of the kind described in the preamble is characterized in that a high emissivity coating is disposed at least on one end of the arc tube proximate to at least one of the electrodes, said coating being the outermost layer of coating on said arc tube end to increase the radiative emissivity of said tube of its location and thereby cool the cold spot of said arc tube.
  • Certain prior lamp designs have utilized coatings disposed proximate to the electrodes or the cold spot of high pressure gas discharge lamps to alter their performance. Such coatings have generally been directed towards increasing the cold spot temperature so as to increase the efficiency or improve colour properties of the lamp.
  • coatings have generally been directed towards increasing the cold spot temperature so as to increase the efficiency or improve colour properties of the lamp.
  • U.S. Patent 3,842,304 to Beyer et al issued October 15, 1974 in which a two layer coating is applied to a high pressure gas discharge lamp so as to increase the cold spot temperature.
  • the outermost coating is that of a white material which serves to lower the emissivity, of the cold spot and thus increase its temperature.
  • an inner coating of carbon material is used for its high thermal radiation absorption properties.
  • the present invention is directed to coating a section of the PCA wall near the cold-spot region with a substance of higher emissivity as to effect a reduction in cold spot temperature. It has occurred to the inventors that this measure effectively reduces the spread in lamp voltage between individual copies of the lamp. This advantageous effect is most probably due to the fact that as soon as the affected region will acquire a higher temperature as a result of an increase of heat input (e.g. by conduction), the power lost by radiation will correspondingly increase and thus effectively counteract the actual temperature increase.
  • coating the PCA with a substance of relative high emissivity will act as a temperature regulator, superior to such regulation as might exist with PCA alone, by virtue of enhanced radiation.
  • a suitable material for increasing this radiated heat loss is graphite, with spectral emissivity between 0.9 - 0.95.
  • the present invention is directed towards decreasing the cold spot temperature so as to minimize the lamp-to-lamp spread between individual lamps of the same nominal wattage.
  • the invention permits manufacture of lamps within tighter voltage tolerances than have hitherto been achieved.
  • the decrease in cold spot temperature may result in a lower actual lamp voltage and thus in some loss in lamp efficiency, however, this may be compensated for by increasing the electrode distance to raise the actual voltage of the lamp.
  • the present invention decreases the "fixture effect". This effect occurs when the mounting of the lamp within various fixtures causes changes in the lamp voltage. Lamps produced in accordance with the present invention display less of a fixture effect than that of previous lamps.
  • FIG 1 illustrates a first configuration of the invention. Shown in Figure 1 is the end of an arc tube 10 which may be in the form of a polycrystalline alumina tube or other suitable material for a high pressure gas discharge arc tube. Extending from the end of arc tube 10 is a niobium tube 12 which makes electrical contact with the electrode 14. This portion of the PCA tube 10 is generally constituting the cold spot. Applied to the end of tube 10 is an annular coating of graphite which serves to increase the thermal emissivity of the arc tube 10 to thereby further cool the cold spot. As is set forth in the experimental results to follow, this provides a reduction in the voltage spread between individual copies of the lamp.
  • the graphite coating 14 was applied by means of a suspension of powdered graphite material in a liquid carrier such as water into which the end of arc tube 10 is dipped. The coating could also be brushed or sprayed on.
  • the coating as shown in Fig. 1 was applied to 1000 Watt and 400 Watt high pressure sodium lamps. Production samples of lamp copies of these wattages were obtained, and the stabilized lamp voltage for each copie of each sample was measured, using a reference ballast. The measurements were made with no coating on the arc-tube, and then with a thin layer of graphite 14 applied to the end region of the PCA arc-tube 10 in the manner shown in Fig. 1. All arc-tubes had identical application of graphite with respect to height H and thickness of layer. In Table I and Table II are presented the stabilized lamp voltages without and with graphite coating. It should be noted that the arc tubes in the lamps shown are the same. The only difference is the application of the graphite coating.
  • Figure 2 illustrates another configuration of the application of a graphite coating.
  • the graphite coating is applied in a strip 16 which does not extend around the arc tube 10.
  • the coating is applied to a height H.
  • the height H of the strip was varied and thus the total surface area of the graphite coating 14 was also varied. The results of these measurements are as follows.
  • Lamp Type 400 W Lamp # Coating Area (mm 2 ) Lamp Volts (No Ctg.) Lamp Volts (With Ctg.) ⁇ V/A (Volt/mm 2 ) A-1 46.6 100.3 82.3 -0.39 A-2 72.4 111.1 85.0 -0.36 A-3 106.5 122.5 81.0 -0.39 It is seen in the last column that in each case, there is a reduction in lamp voltage which is proportional to the surface area of the applied coating. The thus formed proportionality factor can be regarded to be constant for this mode of application. Accordingly, a coating applied in this manner would also be successful in cooling the cold spot and thus providing a reduction in lamp voltage spread.
  • Figure 3 illustrates the dependence of lamp voltage (V 1a ) versus the height (H) of the coating applied in the form of a ring as in Figure 1.
  • V 1a lamp voltage
  • H height
  • Figure 3 illustrates the dependence of lamp voltage (V 1a ) versus the height (H) of the coating applied in the form of a ring as in Figure 1.
  • any material which has a higher emissivity than the arc tube may be used.
  • graphite has one of the highest emissivities, is inexpensive, and is easily applied so that its use is preferred.
  • the coating may be applied to one or both ends of the arc tube.
  • the high emissivity coating "forces" the cold spot to be at its location, coating any one end is generally only necessary.

Landscapes

  • Vessels And Coating Films For Discharge Lamps (AREA)
EP19920200786 1991-03-28 1992-03-19 High pressure gas discharge lamps Expired - Lifetime EP0506182B1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US67693091A 1991-03-28 1991-03-28
US676930 1991-03-28

Publications (3)

Publication Number Publication Date
EP0506182A2 EP0506182A2 (en) 1992-09-30
EP0506182A3 EP0506182A3 (en) 1992-12-30
EP0506182B1 true EP0506182B1 (en) 1996-09-11

Family

ID=24716609

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19920200786 Expired - Lifetime EP0506182B1 (en) 1991-03-28 1992-03-19 High pressure gas discharge lamps

Country Status (4)

Country Link
EP (1) EP0506182B1 (ja)
JP (1) JPH07169442A (ja)
CA (1) CA2063961A1 (ja)
DE (1) DE69213523T2 (ja)

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5331250A (en) * 1990-12-12 1994-07-19 North American Philips Corporation Thick film resistor for use in a vacuum and a high pressure discharge lamp having such a resistor
DE102006002261A1 (de) 2006-01-17 2007-07-19 Patent-Treuhand-Gesellschaft für elektrische Glühlampen mbH Hochdruckentladungslampe
US7728495B2 (en) 2007-08-01 2010-06-01 Osram Sylvania Inc. HID lamp with frit seal thermal control
DE102007045079A1 (de) 2007-09-21 2009-04-02 Osram Gesellschaft mit beschränkter Haftung Hochdruckentladungslampe

Family Cites Families (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
NL7206559A (ja) * 1972-05-16 1973-11-20
JPS5678058A (en) * 1979-11-28 1981-06-26 Mitsubishi Electric Corp Electric discharge lamp
JPS62262357A (ja) * 1986-05-08 1987-11-14 Mitsubishi Mining & Cement Co Ltd 高圧ナトリウムランプ用アルミナ管
EP0366187A1 (en) * 1988-10-24 1990-05-02 Koninklijke Philips Electronics N.V. High-pressure discharge lamp

Also Published As

Publication number Publication date
JPH07169442A (ja) 1995-07-04
EP0506182A2 (en) 1992-09-30
CA2063961A1 (en) 1992-09-29
DE69213523D1 (de) 1996-10-17
EP0506182A3 (en) 1992-12-30
DE69213523T2 (de) 1997-03-13

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