In regards to magical light leaving a ring, there was a discussion a while back that I can't find right now. In a nutshell, the conclusion was that you can create a magical source of light or heat that will shed natural light or heat - which will go beyond the limits of a ring and also bypass a magus' parma (otherwise, parma magica would keep a magus in the cold and in the dark when using magical heat and lighting of insufficient penetration).
In regards to a lab bonus from simple spells, it's tricky. Our troupe finds it contrived and inelegant that if you can cast a spell you get no bonus, while the same effect from a magical item gives a bonus. After a lot of debate and exploring a number of different solutions, we decided to allow any effect to help regardless of whether it comes from a magical item or not. Keep in mind that a formulaic spell requires time to develop (which is far more valuable in our sagas then vis), often "leaves" with the caster, and does not benefit from shape and material bonuses; that a fatiguing spontaneous spell (barring exceptional circumstances) typically entails one botch die and thus roughly one botch and one warping point per season of daily use; and that non-fatiguing spontaneous spells are very, very low level. This does give a little extra oomph to labwork, but it's "paid" by colourful descriptions, very much like resonance (at least the first level) is almost a free bonus to book quality but it gets "paid" by colourful descriptions of a covenant's library.
In regards to item warping, as it's handled now it's one of the very, very few things that we find totally wrong with the Ars Magica system - or more precisely, from the way that the system has evolved over the years (no matter what the authors may claim, the corebook did not give the impression that magic was like radioactive poisoning, quickly corrupting everything around the magus). In our saga, this is one of the very few things that gets house ruled. Items not already aligned with a supernatural realm (such as relics, magical items etc.) do accrue warping points, but these donotimpair the effectiveness of an item except by negotiation within the troupe; and for any negative effect accrued, a positive one of similar magnitude results. The weirdness of items resulting from warping is treated very much in the same way as twilight scars.