Lovely vintage set, called Floulet. It is a sign writing set to work with fluorescent tubes originally

I have shown this with a modern version of a fluorescent tube, a battery operated tube light for photography (this is not included but available elsewhere online)

Great for retail advertising perhaps? 

Lovely to have the original box, with fantastic graphic on the front

At least one of each letter, various fittings and plain colour panels (that can fit behind the letters) too