UGR calculation

Gustavo,  Hi. You are correct in noting that UGR is different depending upon the viewing angle of the observer.  I am not an expert in this field, but I have recently had occasion to learn more - this is what I have discovered:  The credit requires that UGR be calculated on the designed lighting, and you will be setting the "calculation zone" when you model it.  The CEI "default" is 1.2 m (or 3.93 ft.) A.F.F.  You may adjust this if the primary observation level is different for your project (for example if people will primarily be standing rather than sitting in the space).  Because project conditions vary, I don't believe there is a mandatory angle that should be calculated, instead you should set this for the project conditions.  If your project is an office or other space where the workplane is generally considered to be "desk height", I don't see any issue with using the CEI default value.  Hope this helps.