So I know that this is potentially opening up a whole shipment of cans of worms related to illusion spells, invisible doors, and whatnot but...
I noticed an interesting passage in Cannon Companion. Page 112 - underwater spellcasting - illusion spells:
"Mana-based illusion spells are not subject to the refractive distortion caused by water. Illusory objects created by these spells appear at their normal distance and size. Physical illusion spells, on the other hand, are affected by refractive distortion and appear larger and closer than the caster intended. (see underwater perception, p. 111)"
Considering this, along with what we all know about physical illusion affecting mechanical sensors, and it really does seem that while mana illusions are just in the mind, physical illusions actually create photons at the source that travel to an observer's eyes as normal. This is certainly consistent with the refractive quote above and electronic sensors. So if physical illusions actually create photons, or affect their path (steering them around and past an invisible person), then they seem a bit more like a type of manipulation spell than an illusion. That doesn't really bother me, since perhaps the spell categories are more of a spectrum anyway, but I just thought it was interesting and wanted to point it out.

This would mean that a door made invisible by improved invisibility would show what was behind it, but doesn't really decide either way about the mana based illusion. It also affects a lot of the other illusion arguments from these forums.
Hey, look everybody, WORMS!

Look, another can of worms that you missed opening!

It has been pointed out before that most Health spells could be mistaken for Manipulation spells. The same could be said about nearly all Physical spells. However in game balance the Manipulation list is already large enough as it is. I personally could support breaking Elemental Manipulations straight out of Manipulation entirely into an a full fledged Elemental class of spells. It would require an amount of rework of some totems, and some decisions would need to be made surrounding elementalists regarding which spells are prohibited for each element (I think a case by case allowing/disallowing of each Elemental spell is workable there). But overall I think it would be an improvement.

In no way does this need to imply that physical illusions *create* photons, just that such spells alter the behavior of photons - mostly by reflecting them, but also (possibly) refracting/diffracting them in the case of illusory water. You couldnt create an illusory flashlight and have it actually illuminate things, but if someone were looking at your physical illusion with a mirror they would see the illusion.

This makes a small amount of sense when you think of it as the illusion "tricking" the photons into thinking something is there. (or not there, in the case of imp. invis)

What this interpretation would mean, though, is that a physical illusion of a mirror would reflect things the caster does not see (a question discussed at some length a while ago... I'm feeling too lazy to find the thread and link it). As for the door, I did email Rob about that long ago and was told that an invisible door *does* reveal what is on the other side of that door - which is, again, kindof explained by phys illusions tricking photons.

Remember that illusion aided LoS does not count for magical targetting no matter what method you use. But the invisible door can give your gun bunny a clear shot at the mark in the target room (damage reduced by barrier rating of the door, but it's still a fun trick).

If the spell does not create photons how does it create the illusion of any luminous object? Such as a car with headlights on?

EDIT: Or is that a limitation of physical illusions that doesn't apply to mana illusions? That you can't create the illusion of a luminesent object.

EDIT: Following from your interpretation of physical invisibility, by using physical invisibility on a door you are are allowing light to enter the room, right? So if a room is normally dark but next to a lighted area you could make inivisibile the door, wall, ceiling, etc. to light the room.

Poorly.

The caster has to artificially generate that effect by making an illusion of a brighter area in the path of the headlights. Furthermore, the headlights would not illuminate anything beyond the radius of the spell's effect.

EDIT: Yes, that is a restriction I apply to physical illusions that I do not apply to mana illusions. Makes taking mana illusions worthwhile.

To be quite honest, no one in any of the games I've ever played has tried to make an illusion of a car with its headlights on, so I pretty much used the Rectal Extraction Method™ to come up with that answer. Lets just ignore the part about artificial generation and stick with the "poorly."

Physical Illusions create "actual physical data" and one can interpret as they wish. This argument is not new, and Spookymoster brought it up here. I also know that the German rule books actually says "creates and manipulates light and sound" or something to that effect, but I ignore that as poor translation.

My thoughts is that the data transmits from the source point outwards and because the spell is physical it picks up physical ques.