I see... so basically, anything one does with Cr/Mu/Re/Pe Imaginem gets the light wrong. You create the illusion of a big castle? You still get blinded by the sun while resting in its shade. You make someone who's very fat look very thin? The shadow is still fat. You make someone's (heavy) clothes invisible? He won't look naked, he'll look ...matte black, like a ninja. Wizard Sidestep is almost useless in daylight against someone who know's what's going on.
Frankly, this is problematic. I don't think it's at all obvious to the average reader of the corebook.
And I've not even given significant thought to what happens with echoic or olfactive illusions.
It's really a bigger can of worms than Magic Resistance. I'm tempted to say that the easiest fix is that Imaginem works as Phantasmal Force in that other game, as illusions in most legends, so it gets the light right. Mechanically, it would just require Imaginem to be able to manipulate light "entangled" with species, to be able to remove an object's interaction with it, and to create an illusion of light which illuminates just as the real thing. Does not seem like a big deal, and way easier than the frustrating complicated thing this is devolving to.