Background grey after gamma calibration

Hi all,

I am using PsychPy v2022.2.5.
I used a Minolta photometer to gamma calibrate my screen. After gamma calibration this is the table that Psychopy shows:


Min Max Gamma a b k
lum 1.46 194.00000 2.1672 nan nan nan
R 1.46 39.70000 2.4659 nan nan nan
G 1.46 126.0000 2.3054 nan nan nan
B 1.46 19.8000 2.0659 nan nan nan

I do not understand how after gamma calibration the background luminance of the screen is at around 90cd/m2. Can someone explain to me what exactly dictates the luminance of the background grey? Since I will use Gabor patches I want to be 100% sure that they are % michelson contrast. In addition, the background luminance should normally be around 56 cd/m2 so I do not understand why it is as bright as it is.

Help is much appreciated!