(57) By enveloping a gas discharge lamp, such as a fluorescent tube (2), in an outer
glass tube (8), the discharge chamber of the fluorescent tube (2) is thermally insulated.
This enables a sufficiently high temperature to be maintained in the fluorescent tube
(2) for, e.g., mercury in the discharge chamber to be brought to a partial pressure
at which good illuminating efficiency is obtained even at very low ambient temperatures
around the lamp. The tubular envelope (8) is fixated at its ends to the fluorescent
tube (2), in some suitable manner such as to surround the fluorescent tube and define
a tubular space (10) of constant uniform width between the fluorescent tube and the
surrounding envelope. In order to provide a lamp which will ignite readily, the occurrence
of space charges between the fluorescent tube (2) and the outer tube (8) has been
eliminated, by the provision of siloxane seals (11) between the inner fluorescent
tube and the tubular envelope, at the respective ends thereof.
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