(19)
(11) EP 0 081 918 A3

(12) EUROPEAN PATENT APPLICATION

(88) Date of publication A3:
02.05.1984 Bulletin 1984/18

(43) Date of publication A2:
22.06.1983 Bulletin 1983/25

(21) Application number: 82306133

(22) Date of filing: 17.11.1982
(84) Designated Contracting States:
DE FR GB NL

(30) Priority: 11.12.1981 GB 8137489

(71) Applicant: THORN EMI plc
 ()

(72) Inventors:
  • Denbigh, Paul Linley
     ()
  • Jones, Bryan Frederick
     ()

   


(54) High pressure sodium lamps


(57) The invention provides an improved high pressure sodium lamp of nominally 50 watt rating operating at a lamp voltage V of substantially 70-130 volts in which for satisfactory life, efficacy and colour, for an arc tube of internal diameter d in the range 3.0 to 5.0 mm, the sodium mole fraction x, in the range 0.63-0.8, and arc length are determined by interpolation or extrapolation on the graph of Figure 3 or by the equation






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