We are taking 3rd option, measurement to show compliance with the credit requirements.
The text of the credit does not postulate when a regularly occupied area can be considered daylit (for instance, distance from window to the room is given as 15 feet in Lighting Controls credit EAc.1.2).
Does anyone have an idea what is the threshold?
Update: actually, I have found the answer.
this link contains info on how ASHRAE/IES 90.1-2010 defines daylit spaces.