We're developing a new high speed 3d camera system, and in early prototype testing we recently rented a Briese 5K tungsten focus 180, expecting the 5K filament to be flicker-free, but to our disappointment we are seeing flicker in the material filmed with this light.  I remember seeing the bulb, and if my memory is correct it's 4 filaments, so it's probably 1.25K per filament, which explains the flicker.  Glad it was just a test.