I think these are a modern bulb, but never seen these type of bulbs before.

From what I can gather these lamps are used in the production of movies as the color temperatures match the two different color temperatures used in the film industry. Motion picture color film is balanced to either 3200K tungsten lamps or 5500K for natural daylight with the ability to switch between the two as needed (with film speed loss) with filters.

In order to match the fluorescent lamps properly to the film they need to also be balanced to whatever film (or film/filter combination) is being used so the lights show up as white on film. Standard halophosphor fluorescent lamps for example will show up with a green hue on film which is completely unacceptable.

Even in the rare case that black and white reversal film is being used the 5500K lamps may have an advantage as Kodak's Tri-X 200 Reversal motion picture film is a bit more sensitive to light balanced in the 5500K range.

I have some Movie-Tone 3200K lamps, and I wish i could find 5500K ones lol.