Hi Stuart
Just trying to understand and clarify this comment from you:
The FilmGear HMI we have in the shop measures 6000-6300K, depending on settings. That's what I initially expected for the Arri as well. Arri must use better bulbs. It's CRI was much, much higher than the FilmGear fixture.
HMI CCT and color rendering metrics are primarely a product of the brand of bulb/globe, what kind of usage the the globe has been subjected to, globe running hours and age. System parameters like ballast speed/frequency; optical train such as open face vs. Fresnel, typically have lesser impact on the CCT and color rendering metrics.
Filmgear has typically not provided globes/bulbs when the fixtures are sold from us. We normally recommend Osram HMIs (their rated CCT is 6000K) as that is the brand we design and test the fixtures with, but we have no control over what the distributor/dealer/user decides to put in their fixtures.
Can I ask you what particular model fixture and brand of globe that you were testing?