Another process we have been playing with for situations where probes struggle with low-light accuracy is the merging of 2 LUTs generated from 2 different profiles.
For example, using a 21^3 for all data above, say, 10 nits.
And a Grey only profile for below 10 nits.
One of the issues with large profile data sets is the inaccuracy of the readings when the probe is struggling with low-light readings.
Obviously 'colour' readings have less brightness than Grey Scale readings, so cause more inaccuracy in the final calibration LUT.
Using Grey Only data for the low-light range meas such 'read' errors are not included in the LUT generation.
But at higher brightness levels the full volumetric profile data is needs to accurately map the volumetric calibration.
To do such LUT merging the LUT image can be used, via a graphics program such as Photoshop.https://www.lightillusion.com/lut_image.html
Basically you key through the low-luma range from the Grey Only generated LUT into the 21^3 generated LUT...
From this you can see how we can automated such capabilities within LightSpace/ColourSpace.