This is one of the most common flashtubes included in the new Modeling Heads - The front of the yellow UV coated glass dome is open to vent the heat from the Modeling Light.
Modeling flashtubes have a circular design that casts a slightly wider (and more even) distribution of light than conventional tubes, which is why Modeling heads have 1/2 f-stop lower guide numbers - Modeling flashtubes will fit any Lumedyne Head but the Modeling Light itself is only available in Modeling Heads.