Peculiar internal construction of a self-ballasted mercury lamp

This laser shadowgraph reveals the interesting internal design of the Tungsram HMLI 500W. The production of these self-ballasted mercury lamps usually relied heavily on manual labor, especially for the filament assembly. In order to facilitate that step, Tungsram of Hungary used mechanically mounted GLS lamp stems that were produced on standard automated assembly lines. That stem assembly was then mounted upside down above the mercury burner, fixed into place by two spot-welded attachments only.