Method and apparatus to reduce Hg loss in rf capacitively coupled gas discharges

• US 5,146,140 A
• Filed: 06/18/1991
• Issued: 09/08/1992
• Est. Priority Date: 06/18/1991
• Status: Expired due to Term

• Current Assignee: OSRAM Sylvania Inc. (Ams-Osram AG)
• Original Assignee: GTE Products Corporation
• Inventors: Alexandrovich, Benjamin M., Godyak, Valery A., Piejak, Robert B.
• Primary Examiner(s): LaRoche, Eugene R.
• Assistant Examiner(s): ZARABIAN, AMIR
• Application Number:
  US07/717,137
• Time in Patent Office: 448 Days
• Field of Search: 315/248, 315/39, 315/344, 315/267, 313/234, 313/635, 313/607
• US Class Current: 315/248
• CPC Class Codes: H01J 65/046 the field being produced by using capacitive means around the vessel
• CPC Class Codes: H05B 41/24 in which the lamp is fed by high frequency ac, or with separate oscillator frequencyH05B41/26 takes precedence

Abstract

A method and apparatus which prevent mercury and fill gas loss in capacitively coupled electrodeless lamps operated at low frequencies (below 100 MHz). The lamp includes a lamp envelope with an inner coating of phosphor. Outer electrodes coupled to a radio frequency source are positioned around the outer surface of the lamp envelope. The lamp contains a fill gas (e.g. mercury and argon) which forms a plasma causing UV radiation which excites the phosphor. Mercury loss is prevented by providing a pair of inner conductors aligned with the outer conductors but electrically insulated therefrom. The inner conductors prevent the mercury and fill gas ions from embedding themselves in the lamp envelope.

Claims

1. A capacitively coupled lamp comprising

a lamp envelope made of a light transmitting material, said envelope having an outer surface and an inner surface, said inner surface enclosing a fill material which forms during discharge a plasma which emits ultraviolet radiation;

a phosphor layer covering the inner surface of said lamp envelope and emitting visible light when excited by ultraviolet radiation;

a pair of outer conductors positioned on the outer surface of said lamp envelope;

a pair of inner conductors positioned on the inner surface of said lamp envelope and aligned with said pair of outer conductors and electrically insulated therefrom;

an rf source coupled to said outer conductors capable of producing low frequency power below 100 MHz;

wherein low frequency power below 100 MHz applied to said outer conductors induces an electric field in said lamp and discharge therein without loss of said fill material.

2. The lamp according to claim 1 wherein said inner conductors are made of nickel.

3. The lamp according to claim 1 wherein said fill material comprise mercury and argon.

10. The lamp according to claim 1 wherein said fill material comprises mercury and a rare gas.

4. A capacitively coupled lamp comprising:

a lamp envelope having an inner surface and an outer surface, the inner surface enclosing a lamp fill volume;

a phosphor layer covering the inner surface of said lamp envelope which emits visible light when excited by ultraviolet radiation;

a fill material within the lamp fill volume which emits ultraviolet radiation upon breakdown and excitation;

a pair of outer conductors disposed around the outer surface of the lamp envelope capable of coupling low frequency rf power below 100 MHz to said fill material;

a pair of inner conductors disposed on the inner surface of the lamp envelope aligned with the pair of outer conductors and electrically insulated therefrom.

5. The lamp according to claim 4 wherein said fill material includes mercury and at least one inert gas.

6. The lamp according to claim 4 further comprising a source of low frequency power below 100 MHz coupled to said pair of outer conductors.

7. The lamp according to claim 6 wherein the source of power has a frequency in the range from 10 MHz to below 100 MHz.

8. A method of reducing mercury and rare gas loss in a capacitively coupled lamp wherein low freqency rf power below 100 MHz is coupled to the lamp by external electrodes positioned around an outer surface of a lamp envelope, said method comprising the step of:

aligning one or more metal conductors on an inner surface of said lamp envelope with the external electrodes but electrically insulated therefrom, said metal conductors preventing the imbedding of mercury ions and rare gas ions into the lamp envelope during low frequency (below 100 MHz) operation thereby increasing the life of the lamp.

9. The method according to claim 8 wherein the metal conductors are made of nickel.