Illusions, lighting, and reflectance

[Laurefindel]

Again, I strongly disagree that illusions are able to remove things from reality. An illusory wall can't block light, so will instead have a feature that appears to emit the light.

As for illusory pits, well, they are illusions. If you jump into one, you get a surprise and some confusion as you appear to stand on empty air. Probably get advantage on the INT check. There's no mechanic that says you can't walk through an illusionary wall or stand where there's an illusion of a pit.

To that I will add; illusions like minor illusion and silent image should not be a wish type spells where you can recreate all kinds of other spells of lower or higher levels, but with a Int save instead of a Con, Dex or Wis save.

 

[Dausuul]

Again, I strongly disagree that illusions are able to remove things from reality. An illusory wall can't block light, so will instead have a feature that appears to emit the light.

Vision depends entirely on light. You see things when light hits your eyes.

If an illusion cannot block light (or appear to block light), then it is transparent and you can see things behind it.

If an illusion cannot create light (or appear to create light), then you can't see the illusion at all.

If an illusion can block/create reflected light but not emitted light, then things start to get really weird. The sun cannot be hidden by an illusion, but the moon can. You can discern an illusion simply by angling so that it is between you and a light source. Trying to draw such distinctions is far more complicated than simply saying that an illusory wall in front of a light source has the effect of blocking that light source (for creatures that believe the illusion).

To that I will add; illusions like minor illusion and silent image should not be a wish type spells where you can recreate all kinds of other spells of lower or higher levels, but with a Int save instead of a Con, Dex or Wis save.

Please give an example of how this would happen. How would you "recreate" another spell using silent illusion? Keep in mind that silent illusion is automatically revealed by physical contact and can't move except when the caster uses an action to move it; an illusory blindfold over a creature's eyes would fail on multiple fronts (first because the creature is in contact with the blindfold, and second because the creature could take a single step and the blindfold would no longer be over its eyes).

 

[Ovinomancer]

Vision depends entirely on light. You see things when light hits your eyes.

If an illusion cannot block light (or appear to block light), then it is transparent and you can see things behind it.

If an illusion cannot create light (or appear to create light), then you can't see the illusion at all.

If an illusion can block/create reflected light but not emitted light, then things start to get really weird. The sun cannot be hidden by an illusion, but the moon can. You can discern an illusion simply by angling so that it is between you and a light source. Trying to draw such distinctions is far more complicated than simply saying that an illusory wall in front of a light source has the effect of blocking that light source (for creatures that believe the illusion).



Please give an example of how this would happen. How would you "recreate" another spell using silent illusion? Keep in mind that silent illusion is automatically revealed by physical contact and can't move except when the caster uses an action to move it; an illusory blindfold over a creature's eyes would fail on multiple fronts (first because the creature is in contact with the blindfold, and second because the creature could take a single step and the blindfold would no longer be over its eyes).

Illusions are magic, not physics. Insisting the be physical objects leads to weirdness like illusions being able to affect light outside of their AOE.

 

[Dausuul]

Illusions are magic, not physics. Insisting the be physical objects leads to weirdness like illusions being able to affect light outside of their AOE.

You keep claiming this is "weirdness." Why is it weird that an illusion of something blocking a light source can make people think they're in darkness? And do you have any other examples of "weirdness" resulting from this interpretation, or is this literally the only objection you've got?

 

[TaranTheWanderer]

I don't like minor illusion being a mental effect because:

1. It only affects a 5 foot square. So, if you aren't in the square, how is it affecting you if it's mental
2. It means things without minds are immune to it, which isn't the case. Undead and constructs should be fooled unless they have something like blindsight.

How I adjudicate is this:

Everything in the area of the illusion is a visual trick. Like those crazy 3d pictures that you have to stare at for a long time before you see what the image actually is.

So, a torch IN or behind the area of an illusory wall would disappear but the light outside the 5 foot space of the illusion would be real because. The illusion takes on the actual lighting of the area so you might not know exactly where the light is coming from. In a large room, you might be able to narrow it down by looking at the radius of light. The discrepancy lets gives you a clue to investigate. If you throw a rock through it, the rock goes through.

Your brain might tell you that's impossible, but once you go to investigate (maybe with advantage because you threw a rock through the wall), you might see the illusion. (You see the image of the 3d picture.) It doesn't mean you can see through it, it just means you know the area and shape of the illusion. So, just like two people looking at the 3d picture, one person can see the illusion while another can, simultaneously, not see it.

If you fail your check, for all intent and purposes, it looks like a wall but since you threw a rock through the wall, you can probably guess it's an illusion and go ahead and try to walk through it. Let's hope there isn't a pit trap behind the wall because only a successful investigation would let you see if there was.

The disco ball may or may not reflect off the image, because it depends if it's a more powerful illusion. The cantrip won't show the dancing lights because minor image just creates a stationary image. Higher level illusions are more flexible. This does not let you see through the illusion but it might give you a clue that there is an illusory chair, or wall or bed or whatever and give you a reason to investigate the area.

If there's an object hidden inside a magical barrel and you notice the barrel is an illusion, you can surmise what is inside it because you can differentiate between the illusion and reality. I wouldn't say it becomes 'transparent'. This latter example is a bit hand-wavy, I admit.

Lastly, The wall [edit]does not[/edit]gives concealment, whether or not you know it's an illusion. I just re-read the description and, if it does become translucent, it shouldn't give concealment.

 

[Rod Staffwand]

1. Alice is standing in a sealed corridor with a light on the other end. Bob the Illusionist, standing at the other end of the corridor, casts a Minor Illusion (or Silent Image, or something) to create the image of a wall that covers the entire cross-section of the corridor. Does this mean that Alice is now standing in darkness because the wall blocks the light?

Yes. Alice is now standing in darkness unless she perceives the wall to be an illusion. Casting a shadow (blocking light) is one of the primary features of a physical object's appearance. If illusions don't block light, any shifting light source (such as torches) will give away the illusion. Players will quickly learn and start testing for this and I would submit that asking for an Intelligence check while doing so makes the PCs seem like idiots.

2. If not, then consider a more normal case where Alice is looking at Bob in a large room and Bob casts a minor illusion of a wall in front of him to give him cover. Presumably in this case the illusion WOULD block the light that's reflected from the light source off of Bob (if the illusion generated its own light but didn't also stop the light reflected off of Bob, then Alice would just see the wall superimposed on Bob (and the background), since she's seeing both the light from the illusion and the light reflected off of Bob. So does that mean that the illusion can "tell the difference" between light reflected off of Bob and light coming directly from the light source, so it will block one but not the other?

I've read this four times and still don't understand it. In any case, the wall doesn't give cover, but it can give concealment. It looks like a wall to all concerned, except for Bob, who knows it's an illusion an can see through it.

3. If so, consider scenario (1) again but this time, the whole corridor is lit by a light source that is far away, and whose light is reflected off, say, a disco ball at Bob's end. Thus every ray of light that gets to Alice's end of the corridor (without the illusion) was reflected off of some surface at Bob's end. Does this change the answer to question (1)?

No.

4. Can you make an illusion of a mirror, and will it reflect light normally? So you could make an illusionary mirror to peer around corners?

Sure. With minor image the mirror would be stationary.

5. If illusionary objects don't reflect light normally, then the only way illusions could work at all is if they *gave off* light that matched whatever a viewer would actually see when looking at it if it were real. Under that interpretation an illusionary mirror placed across a corner would still show what's around the corner.

True. But minor image states that it doesn't create light so it either REFLECTS/BLOCKS light or it's TRANSLUCENT.

6. Another interpretation that I've seen is that the illusionist decides what the mirror shows - i.e. the illusionist is creating the image. This would imply effectively that (even in a normal case) the illusionist is figuring out what the illusion should look like given the ambient lighting and creating an illusion that shows that. (In other words, the illusionist has repurposed part of his or her brain as a GPU.) Note that this would mean that the illusion would still need to change as ambient light changed (and the illusionist would have to be initially aware of the positions of any light sources, especially if the object the illusion was being made of exhibited high levels of specular reflection).

Ack! Needless complication and waste of time.

7. If you know that an illusion is not real (e.g. because the illusionist who made it told you, or because you saw something pass through it) but you didn't actually spend the action to make the check to examine it, is it still faint/translucent for you? (What if someone who claims to be the illusionist tells you it's an illusion, and it actually is an illusion, but the person who told you isn't the illusionist? If this counts as knowing, it would be easy to get around illusions by having your friend "claim to be the illusionist" and "tell you it's an illusion" every time you see something that might be an illusion.)

Both minor image and silent image have the following text: "If a creature discerns the illusion for what it is, the illusion becomes faint to the creature." So, yes, to the first question. If you see the illusion fail to support a proper physical reaction, you discern the illusion for what it is. Likewise, if you're in a party with Bob and he casts minor image like he's done dozens of times before, you know the illusion for what it is and it appears faint to you (as does Bob, who cast it).

In other circumstances about being told that something is an illusion, you get into matters of authority (does this person know what they're talking about?) and trust (is this person lying to me?), which will be case by case judgement calls. However, I'd usually rule that a check is necessary unless the illusion was cast by a fellow PC. If an NPC you meet tells you a wall is an illusion, you'd need to "check it out for yourself" with a roll or physical interaction.

 

[Ovinomancer]

You keep claiming this is "weirdness." Why is it weird that an illusion of something blocking a light source can make people think they're in darkness? And do you have any other examples of "weirdness" resulting from this interpretation, or is this literally the only objection you've got?

Again, just sticking with spell descriptions, this allows the illusion to affect things outside of it's AOE. Second, this duplicates and can be superior to the darkness spell. Someone has daylight up? Minor illusion of a box neutralizes it.

It also supercharges illusions as tactical tools. Light your ambush area, cast an illusion over the light to darken the area, and ambush your foes who are in darkness while you see them fully lit. I can't believe a 1st level spell can achieve a larger tactical effect than many higher level spells. And all this hinges on the idea that illusions create and block light when such ability is entirely absent from the spell descriptions.

 

[generic]

Again, just sticking with spell descriptions, this allows the illusion to affect things outside of it's AOE. Second, this duplicates and can be superior to the darkness spell. Someone has daylight up? Minor illusion of a box neutralizes it.

It also supercharges illusions as tactical tools. Light your ambush area, cast an illusion over the light to darken the area, and ambush your foes who are in darkness while you see them fully lit. I can't believe a 1st level spell can achieve a larger tactical effect than many higher level spells. And all this hinges on the idea that illusions create and block light when such ability is entirely absent from the spell descriptions.

Furthermore, for illusions to block or create light, they need to be "physical" in the sense that electromagnetic wave radiation and subatomic structures are "physical". This leads to trans-dimensional weirdness on the quantum level, and inconsistent wave mechanics on the macro level.

 

[Dausuul]

Again, just sticking with spell descriptions, this allows the illusion to affect things outside of it's AOE.

Of course illusions affect things outside of their AOE. Illusions work on the minds of their targets; that much is obvious, since different people perceive the same illusion differently depending on whether they've made an Investigation check. And anyone fooled by an illusion is by definition outside of its AOE (if you're inside the AOE, you're physically interacting with it, so it doesn't work).

Second, this duplicates and can be superior to the darkness spell. Someone has daylight up? Minor illusion of a box neutralizes it.

It's not "duplicating" darkness when it only works in very narrowly defined circumstances and can be trivially disrupted. If there are multiple light sources, or the light source is too distant and diffuse to be blocked by a 5-foot object (e.g., you're outside and the sun is up), or the enemy has darkvision, this trick doesn't work at all. And even if it does work, it fails the moment the light source moves! The person with daylight up only has to walk five feet on their turn, and the light pops right back out.

Most indoor light sources can already be shut off by a cantrip. Prestidigitation says explicitly that it can snuff out candles, torches, and campfires. True, it can't target magical light sources; on the other hand, a light source shut off by prestidigitation is really shut off and won't pop back up if somebody moves.

It also supercharges illusions as tactical tools. Light your ambush area, cast an illusion over the light to darken the area, and ambush your foes who are in darkness while you see them fully lit. I can't believe a 1st level spell can achieve a larger tactical effect than many higher level spells.

Your foes can see that the area is (to them) pitch dark before they enter it. Why would they enter without a light source?

 

[TaranTheWanderer]

If you have the illusionist subclass to turn illusions in to semi-real objects, then I'd say they definitely act as object and block light.