Extracting LUX values from HDR (Eye Adaptation)

I have a straightforward question: How can I extract the value shown in the image below and save it as a variable in a blueprint or as text elsewhere?
The menu to access this value is located at Show > Visualize > HDR (Eye Adaptation).
If there are any roundabout solutions you may suggest as an alternative approach, that would be also really helpful.
Thank you in advance.