Applied physics

, Volume 7, Issue 2, pp 93–97 | Cite as

Zur Vergrauung von Entladungsgefäßen

  • Ulrich Kümmel
Contributed Papers

On the darkening of discharge tubes


Vitreous discharge tubes for low-pressure mercury vapor lamps will display after about 1000 hrs of operation a greyish appearance which increases with time. Said darkening can be simulated within a short period of time by applying an electric field transverse to the discharge. The transverse field causes migration of sodium ions of the glass towards the discharge. These ions migrate to the inner surface of the glass where they amalgamate.

Even in normal ac operation of the discharge minor dc Na+ currents pass through the glass of the envelope towards the discharge. The deposited Na atoms amalgamate with the mercury of the discharge on the inner wall surface of the tube thereby producing a light absorbing coating.

Index Headings

Darkening of discharge tubes Damage of vitreous surfaces 


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Copyright information

© Springer-Verlag 1975

Authors and Affiliations

  • Ulrich Kümmel
    • 1
  1. 1.OSRAM-ForschungMünchen 90Fed. Rep. Germany

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