Nice European Osram set there Tim, as far as I know those are/were popular in Germany and other countries where it is traditional to use mainly just white lights on trees. I don`t think that style was particularly common here in the UK though.
I think the set in question is a more traditional British medium-sized series wired 12-bulb set, comparable to the American "C6" series sets. I might even have an example of one with that same colourful box artwork somewhere here. See attached - excuse the poor photo, it`s from years ago and finding that set to take a better one could take some time. I couldn`t find a picture of the lights inside on file, but I have included another old one of a different set which should be similar. As I remember, the Osram set is basically the same layout inside, but the bulbs could be a slightly different shape.
I don`t know a lot about these lights, but perhaps dating from around the 1960s, though the 12-bulb style set was extremely popular from after the war (tended to be normally 16 lights before then) until miniature lights took over in the late 70s. Loads of people made/sold them, and those I have seen are all of a similar construction, bayonet plug to fit a standard wall or table lamp in place of the bulb, then wired in series around in a loop. One bulb goes and they all go out, then you have to hunt through them all for the bad one to get them to work again. They are still fairly collectable especially if the lights themselves are working or otherwise in good condition. Ebay would be a good place to start, even the bulbs listed on their own always seem to sell for a few ???s, although as with anything seasonal, it can vary with the time of year.
