Originally Posted by AnotherDude
Edit: Does the constant luminance affect calibration, or only the interpretation?
Well the saturation sweep charts, that the option affects, are measuring various points along the axis from fully saturated RGBCMY, towards white in the middle. Remember that when you see the full 3D model, such as here
, that (for example), fully saturated blue is much dimmer than fully saturated yellow:
(because it's vertically lower down on the graphic; less luminance)
All those charts ever do is select which points to measure after you've done your calibration. You could measure anything within that volume. If you don't measure points where your TV or calibration has left a problem, you won't spot that problem. Calman measures saturation sweeps and luminance sweeps and various versions of "colour checker".
Setting the constant luminance would mean you are measuring a perfectly horizontal "slice" through the middle, instead of 6 lines at 6 different slopes from the 6 "fully saturated" points.
However, I'm conscious that I could be wrong about the explanation I've just given, so take it with a pinch of salt!