As you know, White Balance consists of Kelvins (blue vs. red color cast) and Tint (green vs. magenta color cast).
“Kelvins" are standard international units used, luckily, by all manufacturers. There are, unfortunately, multiple different standards for “Tint”.
Lumu Light Meter app currently shows green or magenta color cast within a "valid Color Temperature bandpass", defined by the international colorimetric standards. This means that the absolute ratings are always the same, but you can define the number of steps in the app settings.
- if you want to use this measurement with Adobe Lightroom or Camera Raw, you should set the number of steps to 150, because they use +/-150 steps for Tint compensation.
- if you use RED cameras, their Tint number of steps is from -100 to +100.
- if you use it with Nikon cameras, their Tint number of steps is -21 to +21.
However, if you use ARRI cameras or some other equipment you stumble across other units as well:
- Wratten numbers: CC Green & CC Magenta
- plusgreen and minusgreen (used by color filter manufacturers)
Currently we are putting together the overview of all these standards, so they can be incorporated in the app.