Electrodeless Fluorescent Lamp

Home , Electrodeless lamp

^ ^ ^ ^ I ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ ^ I ^ (1 9) European Patent Office Office europeen des brevets EP 0 769 803 A2

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication: (51) |nt CI H01J 65/04, H01J 61/24, 23.04.1997 Bulletin 1997/17 H01 j 61/35 HQ1 j 61/54 H01J 61/70, H01J 61/30 (21)to i \ Applicationa , ♦■ number:k 96307452.1 '

(22) Date of filing: 14.10.1996

(84) Designated Contracting States: • Everest, Steven John DE FR GB IT NL Leicester, Leicestershire, LE4 7PD (GB) • Borowiec, Joseph Christopher (30) Priority: 18.10.1995 GB 9521373 Schenectady, New York 12308 (GB) • Toth, Zoltan (71) Applicant: GENERAL ELECTRIC COMPANY 2200 Monor (HU) Schenectady, NY 12345 (US) (74) Representative: Pedder, James Cuthbert (72) Inventors: GE London Patent Operation, • Forsdyke, Graham Malcolm Essex House, Leicester, Leicestershire, LE9 6RU (GB) 12/13 Essex Street • Michael, Joseph Darryl London WC2R 3AA (GB) University Heights, Ohio 44118 (US)

(54) Electrodeless fluorescent lamp

(57) An electrodeless fluorescent reflector lamp has a discharge vessel (1 ) containing a fill, a solenoid (6) in a reentrant (7) and Indium on the inner wall of the vessel FIG.1 acting as a primary amalgam (20). A secondary amalgam (24) of Indium may be provided on the re-entrant (7). The primary amalgam (20) is preferably under an insulative skirt (12). The vessel (1 ) has a light reflective coating (C) on the inner wall under the skirt (12). The exhaust tube (10) is tipped-off at the proximal end of the reentrant (7) or is omitted the vessel (1 ) being tipped-off at the distal end (9) of the re-entrant (7).

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Printed by Jouve, 75001 PARIS (FR) 1 EP 0 769 803 A2 2

Description oscillation to the solenoid to produce the said field; a housing containing the applying means; an electrically The present invention relates to a discharge vessel insulative skirt extending from the housing and over a for an electrodeless lamp and to an electrodeless fluo- portion of the vessel, the portion of the inner wall of the rescent lamp comprising such a vessel. 5 vessel under the skirt being also coated with light reflec- An electrodeless fluorescent reflector lamp is tive material; Indium amalgam on the inner wall of the known from e.g. EP-A-0,660,375 (PQ-619). Also elec- vessel under the skirt acting as a source of mercury va- trodeless fluorescent lamps are marketed under the por for the fill; and an exhaust tube extending from a trade mark GENURA by General Electric Company. distal end of the reentrant portion remote from the hous- Such lamps comprise a discharge vessel the inner wall 10 ing and tipped-off at the proximal end of the reentrant of which is coated inter alia with a transparent electri- portion. cally conductive material, and phosphor. The vessel According to another aspect, there is provided an contains a fill which is energised by an RF magnetic field electrodeless fluorescent reflector lamp comprising: a to induce a discharge therein. The RF field is produced closed discharge vessel having a reentrant portion, the by a solenoid housed in a re-entrant portion of the ves- is vessel containing a fill which when energised sustains sel. The solenoid is energised by an RF oscillator in turn a discharge; the inner wall of the vessel being coated energised from the mains via a rectifier. The oscillator with at least a layer of light transmissive electrically con- and rectifier are in a ballast housing which supports the ductive material and phosphor; a solenoid in the reen- solenoid and discharge vessel. A skirt extends from the trant for energising the fill with an RF magnetic field; housing over part of the surface of the discharge vessel. 20 means for applying an RF electrical oscillation to the so- A light reflective layer is provided on the internal surface lenoid to produce the said field; a housing containing the of the vessel under the skirt. An exhaust tube extends applying means; a skirt extending from the housing and from the inner end of the re-entrant through the solenoid over a portion of the vessel, the portion inner wall of the to a position adjacent the oscillator/rectifier circuitry in vessel under the skirt being also coated with light reflec- the ballast housing of stable temperature in operation. ts tive material; and Indium amalgam on the inner wall of A pellet of e.g. lead/bismuth/tin mercury amalgam is the vessel under the skirt acting as a source of mercury held in the exhaust tube remote from the vessel. The vapor for the fill; the discharge vessel being tipped off pellet is the sole source of mercury vapour of the fill. The at the distal end of the re-entrant remote from the hous- position of the pellet is chosen so that in operation of ing. the lamp the temperature is stable and of the correct 30 Because the primary source of mercury vapour is level to produce the vapour pressure for optimum light in the vessel, the exhaust tube is either no longer need- output for the type of amalgam used. ed or it need not extend into the ballast housing giving Because the tube extends into the housing, the cir- greater freedom for arranging circuit board(s) within the cuit board or boards of the oscillator and rectifier are housing. Also the need to place a pellet of amalgam in arranged around the tube. This reduces the options for 35 the tube and to hold it there is avoided. arranging and supporting the boards in the ballast hous- For a better understanding of the present invention, ing and/or increases manufacturing costs. Furthermore, reference will now be made by way of example to the providing the pellet of amalgam in the exhaust tube and accompanying drawings in which : holding it therein, complicates manufacture of the lamp. Figure 1 is a schematic diagram of an illustrate US-A-4262231 discloses an electrodeless fluores- 40 electrodeless fluorescent lamp embodying the inven- cent lamp having a discharge vessel having a solenoid tion. for energising the fill to produce the discharge. The so- Referring to Figure 1 the lamp comprises a dis- lenoid is not physically isolated from the discharge. Mer- charge vessel 1 of glass supported by an electrically in- cury vapour is provided by a lead-tin-bismuth amalgam sulative ballast housing 2 to which is connected a lamp placed on an interior surface of the envelope. The amal- 45 cap 3 such as an Edison-Screw cap. The shape of the gam is fixed to the glass wall of the envelope via a layer vessel approximates to that of known incandescent re- Indium. flector lamps as sold by GE Lighting Limited: an exam- In US-A-4262231 the source of mercury vapour is ple of such a lamp is an R80 lamp. The housing 2 houses not the Indium but the lead-tin-bismuth amalgam. a rectifier 4 and an RF oscillator 5 energised by the rec- According to one aspect of the present invention, so tifier 4. The oscillator 5 energises a solenoid 6 which is there is provided an electrodeless fluorescent reflector housed in a re-entrant portion 7 of the vessel 1 . An ex- lamp comprising: a closed discharge vessel having a haust tube 8 extends from the distal end 9 of the re- reentrant portion, the vessel containing a fill which when entrant 7 innermost of the vessel to the proximal end 1 0 energised sustains a discharge; the inner wall of the of the re-entrant adjacent the ballast housing 2 where it vessel being coated with at least a layer of light trans- 55 is tipped-off. missive electrically conductive material and phosphor; A skirt 12 of opaque insulative material extends a solenoid in the reentrant for energising the fill with an from the housing 2 over the discharge vessel to the zone RF magnetic field; means for applying an RF electrical of greatest diameter of the vessel.

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The vessel 1 is internally coated with an internal hausttube 10. coating C comprising:

(a) a layer of electrically conductive transparent ma- Claims terial on the glass wall, to confine the RF field with s the vessel; 1. An electrodelesselectro fluorescent reflector lamp com- (b) material on the conductive coating which pre- prising: vents blackening of the glass by mercury during ex- tended operation of the lamp; a closedclos discharge vessel having a reentrant (c) a light reflective layer over the portion of the in- 10 portion,portior the vessel containing a fill which when ternal surface under the skirt 12; and energisedenergi sustains a discharge; the inner wall (d) phosphor over the reflective layer; all the mate- of the vessel being coated with at least a layer rials being known in the art. of lightlighl transmissive electrically conductive material and£ phosphor; The discharge vessel contains a fill as known in the 15 aasolei solenoid in the reentrant for energising the fill art. The fill is energised by the RF magnetic field to pro- with anai RF magnetic field; duce a discharge. The primary source of mercury va- means for applying an RF electrical oscillation pour of the fill is a piece of Indium 20 (shown schemat- to the solenoid to produce the said field; ically) on the internal surface of the vessel. The Indium a housinghous containing the applying means; 20 forms an amalgam with mercury introduced into the 20 an electricallyele insulative skirt extending from vessel during manufacture thereof. When the lamp is the housinghe and over a portion of the vessel, energised, the Indium releases the mercury. When the the portionpo of the inner wall of the vessel under lamp is de-energised the mercury re-amalgamates with the skirtsk being also coated with light reflective the Indium. material;materi The Indium is placed on the internal wall at a posi- 25 IndiumIndiurr amalgam on the inner wall of the vessel tion at which in stable operation of the lamp, the tern- under the skirt acting as a source of mercury perature is appropriate to produce the mercury vapour vapor for the fill; and pressure for optimum light output. That optimum pres- an exhaustexr tube extending from a distal end of sure is preferably 0.8 Pa. the reentrantrei portion remote from the housing The mercury may be introduced during manufac- 30 and tipped-offtif at the proximal end of the reen- ture of the lamp or be already amalgamated with the trant portion.p piece of Indium 20 or by the use of a pellet of zinc 22 amalgamated with mercury. The zinc pellet 22 releases 2. A lamp accordingac to Claim 1, wherein there is no 95% of the mercury once heated to 90°C. The released amalgam ini the exhaust tube. mercury amalgamates with the Indium 20. The Indium 35 is preferably provided on the glass vessel under the in- 3. An electrodelesselectro fluorescent reflector lamp com- ternal coating C. Alternatively, the coating C may be prising: omitted from the region occupied by the Indium. The In- dium 20 may be in the form of a spot or a band. a closedclos discharge vessel having a reentrant A secondary source 24 of mercury vapour may, op- 40 portion,portior the vessel containing a fill which when tionally, be provided in the form of a piece of indium on energisedenergi sustains a discharge; the re-entrant to provide quicker "run-up" of the lamp. the innerinr wall of the vessel being coated with The secondary source is placed adjacent the discharge at leastleas a layer of light transmissive electrically to be quickly heated. The secondary source is provided conductivecondu material and phosphor; in a zone of the re-entrant on the conductive coating but 45 aasolei solenoid in the reentrant for energising the fill otherwise devoid of coating C or it may be under the with anai RF magnetic field; coating C. means for applying an RF electrical oscillation The Indium is preferably provided at the zone of to the solenoid to produce the said field; greatest diameter of the glass vessel under the skirt 20 a housinghous containing the applying means; so that it is not visible to a user of the lamp. so a skirt extending from the housing and over a The exhaust tube 10 may be omitted. The vessel 1 portionportior of the vessel, the portion inner wall of is then evacuated of air and provided with the fill via an the vesselve: under the skirt being also coated with opening in the end 9 of reentrant which is then sealed. light reflectiverc material; and Because the exhaust tube 10 does not extend into IndiumIndiurr amalgam on the inner wall of the vessel the housing 2, the circuit board(s) of the oscillator and 55 under the skirt acting as a source of mercury rectifier may be arranged without taking account of the vapor for the fill; tube 1 0. Because the source(s) of mercury vapor are in the dischargedis vessel being tipped off at the dis- the discharge vessel, no amalgam is needed in the ex- tal endenc of the re-entrant remote from the hous-

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ing.

A lamp according to Claim 2 or 3 wherein the said Indium is the primary source of mercury vapor and further comprising Indium amalgam on the reen- s trant portion acting as a secondary source of mercury vapor.

A lamp according to claim 1 , 2, 3 or 4, further comprising a pellet of zinc amalgam within the discharge 10 vessel.

55 U I S3 OVO H£.

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