The most common interpretation of ring/circle seems to be that it affects a sphere defined by the size of the ring.
Hypothetical question: Would it therefore be possible to affect a spheres worth of something using a ring. For instance, imagine a glass sphere, filled with a liquid. The sphere has a thin line engraved around the outside across its circumference. By casting a ring/circle spell could one affect all the water in the sphere?
I'm not sure that is a common interpretation. I've never considered a 6ft tall man to only be protected from the waist down if he's standing in circular ward with a 3ft diameter.
My view has always been of a column with a somewhat undefined height. If a target fully fits within the area then it's covered height wise, this applies wether its a pancake or a step ladder. When dealing with amorphous targets it should be a case by case basis with "not to silly" as the goal.
That being said a glass sphere with it's circumference marked as the boundary of the spell is okay in my book for most effects. Though I've used buckets, bottles and cups myself.
In ArM5 corebook the various ward spells were described to have slight visual cue shaped like dome with one colour or another.
But if that is true for all cirlce spells or just speciality of wards, or even merely cosmetic effect...
Legacy element.
I'm gong to just come right out and state that I advice against the use of D: Ring (and T: Circle) in devices.
Use Constant effect instead - it's just 4 more levels (not even magnitudes, just levels), and you won't have to fiddle around with something that might not be kosher.
You are talking about D:Sun with Environmental trigger (+3) at Sunrise/-set and 2 uses/day (+1), right?
Actually I was hoping to avoid enchanting an item at all by using ring/circle to make a permanent spell.
The item I had in mind was a small glass sphere enchanted as a lesser item to remain in any place it it put (i.e. low level ReTe)
The ring carved around the circumference would then make the insides glow brightly but importantly would be a spell cast on the sphere rather than an effect enchanted into it. This allows the sphere to be made as lesser enchanted devices and gives us hovering lights. Very chic.
Yes, this is the real advantage of using Ring/Circle. You get something more "fragile", but that costs you no vis or time to make.
Alas, you contradict your own philosophy! Affix the ring to the sphere (more precisely around it), and cast the ReTe spell that "anchors" in place all glass within the ring unless a moderate force is exerted on it.
Or you could make a Ring/Circle CrIg spell to generate the light directly?
A small hovering thingie carries a piece of flat board with a CrIg spell on it.
Could you make the hovering effect Ring/Circle (or Ring/Ind) too? plausibly.
Note that Ring/Circle CrIg is tricky, because the light disappears as soon as it leaves the Ring. Thus, you can illuminate within the Ring, but not outside it.
But you could generate it slightly less directly and not have this problem. The key is to create a source of illumination, not the illumination itself. Then only the source is contained in the circle, not the illumination. For example, at the end of a metal rod make a circle/ring and enchant that with a torch-equivalent fire. That fire gives off natural light that extends beyond the ring. Now you have a nearly permanent torch that can be carried for lighting. The same could be done for a lantern and then you could adjust the amount of light, or for what are essentially candles that could be placed in candle holders of various sorts.
Chris
This is not entirely clear. If you create a magical fire, the "direct heat" emanating from it is magical (it does not burn someone protected by parma) and thus should not be able to leave the Ring. Something similar should apply to light.
Now, in the case of heat, you can heat something magically, and that something will shed non-magical heat. However, it's not obvious to me that the same can apply to illumination. If you illuminate something, does that something shed non-magical illumination? I'd be tempted to say no, but I guess it's widely open to interpretation.
You're right.
About Ring/Circle certainly.
Not so sure about Ring/Ind.
Noble's Parma.
So if I do CrTe ring/circle block of stone it's invisible to people until they smack their faces on it?
Chris
No, because the species shed are natural. But that's different from light and heat.
If you are protected by Parma you see a Pilum of Fire, but it can't burn you.
Actually, I should not have written Ring/Circle, but simply Ring. CrIg with target Circle is controversial at best (because all Creo spells that create something are supposed to do so with target Ind or Group, corebook p.113), but Ring duration ends if "the target of the spell moves outside"(corebook p.112).
Absolutely correct, my bad.
I would still accept a Ring/Ind flame illuminating a room, despite the bit about the effect ending when leaving the circle.
The use of light in percieving species troubles me anyway 
Ok, bad attempt. Let me do better to show the problem. Magus 1 casts Pilum of Fire at Grog 1 in a pitch black room. Magus 2 hears Grog 1 scream but does not see the flame. Why not? Light carries visual species and without it the species cannot reach Magus 2's eyes, and the only light available is from the Pilum. Do we really not want Magus 2 to see Magus 1's Pilum?
Chris
It's a very contrived scenario. Here's a simpler version. Magus in a dark, dark room creates a magical light (through CrIg) with low penetration -- not enough to bypass his parma. Do we really want him to be the only one in the room who remains unseeing? I believe the magus would see everything the light illuminates in the room.
Species are carried by light, and magical light stops right at the contact point with the magus. But species are not magical, so once they are in contact with the magus, they affect his senses -- a little like a passenger can get from a boat onto the dock, even though the boat itself cannot get onto the dock. More fitting examples are possibly those given on p.85 of the corebook: "a jet of normal water driven by magic reaches the maga and makes her wet, but has no force of impact", and "a rock thrown by magic stops at her skin or clothes. The maga ... feels the rock touching her ... but she is not struck by the rock." It seems clear to me then, that if a magical medium carries something non-magical all the way to the magus, that something can touch the magus and affect him, even though the magical medium is prevented from doing so.
If there are no natural source of light and no light reaches the magus, he will emit dark species that carry no image. He won't be blind, he will be as invisible as a dark blob in a clear room.
I'm thinking it might actually be easier now to enchant the globes to emit light and then use the ring/circle effect to levitate the globe. It would certainly get around the light/ring issue.