(57) improved ceramic seals for both ends of a tubular light transmitting ceramic envelope
used in sodium vapor lamps are disclosed to provide a more reliable hermetic seal.
One end closure comprises a ceramic plug inserted into one end of the light transmitting
envelope and being hermetically sealed to the inner wall of said envelope with ceramic
sealing frit, said ceramic plug having a central opening through which extends one
thermionic electrode inlead which is hermetically sealed at said opening with ceramic
sealing frit, and having a transverse metal cross piece joined to said inlead. The
remaining end closure comprises a ceramic disc having a larger diameter than the inner
diameter of said light transmitting envelope which is hermetically sealed with ceramic
sealing frit to the end of said light transmitting envelope as well as to the surface
of a ceramic plug inserted into the end of said light transmitting envelope, with
both said ceramic disc and ceramic plug having central openings through which extends
an inlead and exhaust tube member for the remaining thermionic electrode and which
is hermetically sealed at the central opening of said ceramic plug with ceramic sealing
frit.
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