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« Last post by adam2 on March 20, 2021, 08:56:45 pm »
It looks like a fairly standard type of mercury vapour lamp.
Many mercury vapour lamps have a fluorescent coating in order to improve the colour of the light, but this is a clear or uncoated type.
This type of lamp has two main electrodes between which the current passes, one at the top and one at the bottom. A third small electrode connected via a high value resistance may be seen at the bottom of the lamp. This assists in starting from line voltage without any external high voltage starting device.
Not easy to date as they have been made to the same basic design for decades.
Such lamps are intended to be connected to the mains via a choke or ballast. Connection without this required choke or ballast is apt to destroy the lamp.
Unlikely to be of value, but don't rush to chuck it out just in case.