Out of curiousity, where are you drawing that distinction from? No hostility intended, I just don't recall that description of shadow in the Imaginem header, and personally, I don't think you can have shadows without having light... in my mind, shadows are where there is no or little light, rather than no or little image, and that would make them Ignem. To have no image would be invisibility, not darkness or shadow. If there's a clearer reference on this I'm missing, please let me know.
Lucius: I can't think of a single canonical spell that allows a nonHermetic target/range/duration for a bump in magnitude.(Serf's Parma!) Any that did something obviously outside Hermetic Laws are usually labeled Mercurian and given a magnitude of "that's-the-way-it-is." If you could just throw in a new target/range/duration for a magnitude bump, why would you ever try to research a breakthrough? I don't think you can do it the way you describe.
Two items that came to mind to further the research into a minor breakthrough that I think a Range:shadows would be are:
A bronze mask that has two instilled effects:
InIg 30 (as above but with concentration duration), +5 item maintains concentration
InIm 25 (Base 1, +3 sight, +1 concentration, +4 vision) and +5 Item maintains concentration.
This would let a user see all the shadows in a structure and then look out from those shadows as he desired. Basically a "the-walls-have-eyes" sort of effect.
a set of pan pipes with two instilled effects:
InIg 30 (from above), +5 to maintain concentration
CrAn 30 (Base 5, +3 sight, +1 diameter, +1 size) +5 for 12/day? (serf's parma)
this would let a user see all shadows in a structure and then create 10 big, hairy, dinner plate sized spiders to pour out of those shadows and do spidery-type things for 2 minutes before disappearing. I would guess that for the appropriate S&M bonuses to apply they should rats, but I think spiders are creepier.
these two items, if completed appropriately in the breakthrough dance, would provide 12 and 14 breakthrough points respectively, and after the first item I suggested, you'd have enough there to get your new range:shadows.
Over all, I think range:shadows could be very cool. I'd likely put it's magnitude bump at +3... like duration:sun ... it has strengths, but also weaknesses; it might be impossible in an area under the effect of a CrIg spell that destroys all shadows... (Or would it be a PeIg...or as Ulf describes it, a CrIm effect? Hrm.) I'd allow the caster to have his effect emanate from any shadow within a naturally occuring boundary, like a forest, or a structure, or a town... on a plain at noon this range would likely be very short, but at dusk, it could be much better... I think it's further than sight but definitely less than arcane connection ...and not worth a +4 bump, but that's just my thoughts on it.