That arrangement was used on British rail MK3 coaches and multiple units based on MK3 coaches, a 1970s design. By the 70s, they ussually have a 110v DC supply for lighting with an electronic ballast. Earlier trains used different voltages. I have an image of a ballast in my gallary, the standard ballast was smart and brown. Thorn seemed to supply the parts like lampholders for BR lighting. Orignally the diffusers would have been opal, they were changed as part of a refurb at some time. I've always been fascinated by train lighting and really like that design.