The Mechanics of Lightweaving (edit: On Roshar; not Yolen)

[TheFlatScadrian]

So, I was reading Stormlight, and apparently Lightweavers can't see through the other side of their illusions, which struck me as odd.

Most people discuss Lightweaving as a generation of light and sound, rather than just a manipulation of it. But if the illusions are generating light, then you would be able to see through illusions from the other side, because you could just have the light shine outward without it shining inward. You also wouldn't be able to make total darkness inside a covering, because even the darkest illusions would still generate some visible light.

What I think is actually happening is that the Lightweaving illusions are more like a false ontology of an object, one that tricks ambient light and air into interacting like there's something there even when there isn't.

So, if you're making an illusion of, say, a stick, you're not generating light that shines in the form of a stick, you're using Investiture to maintain the idea of a stick, that light and air then interact with as if it where real.

If they were generating light, then the ambient light, which would normally shine through the illusion, would have to be simultaneously manipulated around the illusion, which might make some angles appear "brighter" for no particular reason, possibly making a faint but visible halo around an illusion. The same would be even more noticeable with sound, where generated sound waves would cause the need to displace or redirect ambient sound waves in odd ways. 

This even plays into the idea that Lightweavers can soulcast their illusions; they're making the illusory shape physical.

(This still works for lasers and darkness, because it's simply a less defined version of ambient light manipulation. Thinking of illusions as "fake things" is really more of a way to conceptualize it than how it actually works on a fundamental level, but the standard holds.)

So my question is this:

Does Lightweaving generate light and sound? Or can it only manipulate ambient light and sound? 

And secondarily, if they can't generate light and sound, and only manipulate it, can they then manipulate the frequency of waves, or just their direction? Light is already visually additive, so they could turn just three colors into many different hues and shades without changing wavelengths.  

(And this matters, because if they can't generate light or sound, then in Era 2 Infrared cameras could see through fake Lightweavings of living things, because biological-low-band-infrared isn't common in ambient space and couldn't be manipulated, and if they can generate light and sound, than radar waves would have strange bouncing effects when being manipulated by Lightweavers) 

Edited December 8, 2025 by TheFlatScadrian

[Muse]

I'm sure this is topic is a bit hand-wavy since its "magic" and it has not been spelled out explicitly apart from the info we know from descriptions of usage, but if I were to speculate based on what we know, I agree with your take that visual illusions, as we've seen them, probably don't operate by generating light. Instead, they likely generate illusory pseudo-matter and energy with Investiture that interacts with the environment (e.g. ambient light) such that a particular image is perceived by others. Many of your observations lend to this idea.

That said, sound waves are a slightly different phenomenon than light waves because light comes from an external source, bounces off matter and reflects into a sensor like an eye while a voice (as a sound wave) comes from vibrations in the vocal cords and vibrate air molecules propagating out from the person speaking. This would either require the illusion to cause some physical manifestation from the illusion (e.g. vibrate vocal cords) or to actually generate sound waves. Since the illusions are generally not material and can't cause this vibration, it seems like the illusion would have to directly generate sound waves (since there are no physical vocal cords to generate that sound).

From this, I gather that a Lightweaver can both manipulate and generate light / sound waves, whatever is needed to match the physical phenomenon they are trying to create. If this were true, I think this would also allow the Lightweaver to generate light in a dark room (I can't think of any examples of this happening off hand, but seems like a way to confirm or deny this theory).

Either way, if all this is true, then Lightweavers can likely manipulate frequency and direction of waves as well as generate waves in specific direction as they can probably manipulate the perception of matter to match the Lightweaver's intent.

One last note that seems in line with this hypothesis (WaT spoiler):

Spoiler

Shallan is able to physically manifest Radiant to attack Abidi the Monarch, which seems like a step up from pseudo-matter to real matter, so it is a more advanced variation of the same phenomenon (generating pseudo-matter which can interact with and generate light /sound waves then "levels up" to generating actual matter, which can then also physically interact with other matter, not just influence light & sound).

Edited December 8, 2025 by Muse

[Dunkum he/him]

2 hours ago, Muse said:

I'm sure this is topic is a bit hand-wavy since its "magic" and it has not been spelled out explicitly apart from the info we know from descriptions of usage, but if I were to speculate based on what we know, I agree with your take that visual illusions, as we've seen them, probably don't operate by generating light. Instead, they likely generate illusory pseudo-matter and energy with Investiture that interacts with the environment (e.g. ambient light) such that a particular image is perceived by others. Many of your observations lend to this idea.

That said, sound waves are a slightly different phenomenon than light waves because light comes from an external source, bounces off matter and reflects into a sensor like an eye while a voice (as a sound wave) comes from vibrations in the vocal cords and vibrate air molecules propagating out from the person speaking. This would either require the illusion to cause some physical manifestation from the illusion (e.g. vibrate vocal cords) or to actually generate sound waves. Since the illusions are generally not material and can't cause this vibration, it seems like the illusion would have to directly generate sound waves (since there are no physical vocal cords to generate that sound).

From this, I gather that a Lightweaver can both manipulate and generate light / sound waves, whatever is needed to match the physical phenomenon they are trying to create. If this were true, I think this would also allow the Lightweaver to generate light in a dark room (I can't think of any examples of this happening off hand, but seems like a way to confirm or deny this theory).

Either way, if all this is true, then Lightweavers can likely manipulate frequency and direction of waves as well as generate waves in specific direction as they can probably manipulate the perception of matter to match the Lightweaver's intent.

One last note that seems in line with this hypothesis (WaT spoiler):

  Hide contents

Shallan is able to physically manifest Radiant to attack Abidi the Monarch, which seems like a step up from pseudo-matter to real matter, so it is a more advanced variation of the same phenomenon (generating pseudo-matter which can interact with and generate light /sound waves then "levels up" to generating actual matter, which can then also physically interact with other matter, not just influence light & sound).

Was going to say something similar. though I did want to add for completeness: being able to manipulate sound in similar ways as light is important too, overall. if you make an illusion of a cave, but it doesn't echo correctly when someone yells into it, it would blow the whole thing

[TheFlatScadrian]

19 hours ago, Muse said:

That said, sound waves are a slightly different phenomenon than light waves because light comes from an external source, bounces off matter and reflects into a sensor like an eye while a voice (as a sound wave) comes from vibrations in the vocal cords and vibrate air molecules propagating out from the person speaking. This would either require the illusion to cause some physical manifestation from the illusion (e.g. vibrate vocal cords) or to actually generate sound waves. Since the illusions are generally not material and can't cause this vibration, it seems like the illusion would have to directly generate sound waves (since there are no physical vocal cords to generate that sound).

I think that's right, but I'd also wonder as to how that generation differs.

Air molecules can exist without being in a wave, but photons can't. It think you're right that Lightweavers could generate sound, but I also think that it still fits my thesis.

It'd similar to just moving yourself and generating sound that way. I don't think they could generate air molecules that have a vector already, like generating light, but I think they can exert force on the particles to make sound, like they can with ambient light. 

Of course, light is weirdly both wave and particle simultaneously, so it could go either way.

19 hours ago, Muse said:

generate light in a dark room

I tend to think that when they do stuff like this, or the opposite (Walls of darkness), they're just dispersing or gathering the limited light around them into or away from an area. There's always some ambient light around to do this, even in deep space.

Could they dampen sound, too? Make a sound bubble?

Edited December 9, 2025 by TheFlatScadrian

[Nitpicking]

On 12/8/2025 at 7:18 PM, Dunkum said:

Shallan is able to physically manifest Radiant to attack Abidi the Monarch, which seems like a step up from pseudo-matter to real matter, so it is a more advanced variation of the same phenomenon (generating pseudo-matter which can interact with and generate light /sound waves then "levels up" to generating actual matter, which can then also physically interact with other matter, not just influence light & sound).

Well, but remember her other Surge is Soulcasting. She can literally manifest matter (by transforming air into it). At the high end, one suspects her Surges blend.

[Dunkum he/him]

1 hour ago, Nitpicking said:

Well, but remember her other Surge is Soulcasting. She can literally manifest matter (by transforming air into it). At the high end, one suspects her Surges blend.

sure, but the impression I always got was that soulcasting takes a lot more investiture than lightweaving. so yes that is possible, but may not be the best use of resources.

[First of the Tide He/him]

1 hour ago, Dunkum said:

sure, but the impression I always got was that soulcasting takes a lot more investiture than lightweaving. so yes that is possible, but may not be the best use of resources.

Sure, but if light weaving can essentially do exactly the same thing as soulcasting, but for cheaper, then there is no purpose in an entire surge, and that feels incredibly redundant, and not a narrative choice sando would make. I think it's something similar to windrunner's reverse lashing, where it's a combination of both, and also takes comparitively little stormlight, even compared to each of the other surges individually.

(maybe not quite so comparitively little, but similar or less than such an advanced and complex lightweaving) 

Also, keep in mind that Shallan is 

Spoilers for late SA

Spoiler

The daughter of a herald and bonded to 2 spren, both of which sando has said makes her a stronger, more uniquely powered Surgebinder. She transported herself into shadesmar, which she could only do because of her double sprens

 

[Brgst13]

I think that the Lightweaving itself is an Investiture construct.  The Investiture in that construct emits light much like an electrical spark does.  It is possible as well that the Investiture absorbs incoming light and radiates it on a different wavelength.