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It's looks to be a flame-proof fitting, which makes sense if explosives were stored there during WW2. My father worked as a toolmaker in a factory during WW2. He said that many factories used mercury lighting, but it was unsafe where machines were working because under certain circumstances, things looked as if they were running backwards; lathes and drilling machines for instance, caused by a 'strobe effect' from the lights. I remember him saying that a number of accidents resulted.

I am sure I've seen that type of light fitting somewhere else before. Unless it was if BBC's 'Coast' (or something similar) had an episode that featured those bunkers/tunnels. Claire is right though in that it should have a glass cover as it would have been flame proof.

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