(19)
(11) EP 0 506 182 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
30.12.1992 Bulletin 1992/53

(43) Date of publication A2:
30.09.1992 Bulletin 1992/40

(21) Application number: 92200786.9

(22) Date of filing: 19.03.1992
(51) International Patent Classification (IPC)5: H01J 61/35, H01J 61/24
(84) Designated Contracting States:
BE DE FR GB IT NL

(30) Priority: 28.03.1991 US 676930

(71) Applicant: Philips Electronics N.V.
5621 BA Eindhoven (NL)

(72) Inventors:
  • Ramaiah, Raghu
    NL-5656 AA Eindhoven (NL)
  • Kimmel, Suzette
    NL-5656 AA Eindhoven (NL)

(74) Representative: Dusseldorp, Jan Charles et al
INTERNATIONAAL OCTROOIBUREAU B.V., Prof. Holstlaan 6
5656 AA Eindhoven
5656 AA Eindhoven (NL)


(56) References cited: : 
   
       


    (54) High pressure gas discharge lamps


    (57) An improved high pressure gas discharge lamp. The lamp contains a standard arc tube (10) having electrodes (13) disposed at each end. The outer surface of at least one end of the arc tube is coated with a layer (14) of high radiative emissive material such as graphite or carbon. The coating serves to increase the radiative output of the arc tube at its so-called cold spot so as to cool the cold spot. The coating greatly decreases the voltage variation from lamp to lamp and permits manufacture of lamps within tighter voltage tolerances than have hitherto been achieved.






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