Does light go around corners?

[pauljathome]

This issue came up today in PFS. I'm interested in the RAW answer.

I'm not talking about the interaction of light and darkness spells, just asking about basic light from a sunrod (so, 30 ft bright light).

In the following example, how far would the light go? How far would the person P standing at the corner be able to see down the corridor? Would low light vision change that answer?

X - corridor
L - light source
P - Person

PXXXXXXXX
X
X
X
L

[andreww]

I am similarly interested in the answer to this question although it should perhaps be in the rules forum.

[CrescentCrux]

Mechanical wise light does not travel around corners (though it does circle a globe which is why we get sunset sunrise.) But it does increase ambient light a bit. Ever shine a light forward to see well in one spot? Well turn that light upright and it adds a bit of light to the room over all. Shiny surfaces(polished stone or mirrors) can scatter light in other directions.

A normal vision Human would probably get no more then a foot or two, Elf a few feet more, and Darkvision doesnt care ;p.

RAW, no you would get no light for it.

EDIT; I should add Light blindness as a note, when looking from an area of light out to darkness you can not as easily see because your eyes are adjusting to light. This is an idea why pirates wore an eye patch (bright deck vs dark galley) to counter the light different.

[Kazaan]

There's no hard and fast rule for applying it, but I would say that it works as follows:

Presuming Sunrod w/ 30' Normal Light and 30' more +1 current level.
Count diagonally across the corner as normal light if it's within the "normal light" radius of the light source. Additional spaces after this first diagonal are counted as "+1 level" out the the extend of the first radius. No effect beyond this. To illustrate;

20' away from opening of corridor
PN++XXXXXX
N
N
N
L

15' away
PN+++XXXXXX
N
N
L

10' away
PN++++XXXXX
N
L

5' away
PNNNNNN++++++XXXX
L

So, basically, count out the first full 30' radius (in the case of a Sunrod) and squares after the "first diagonal" around the corner are treated as dim light if starting from darkness (normal light if starting from dim) and the "+1 level" ends at 30' (where, ordinarily, the normal light would end). This roughly simulates the reflection of light around the corner if the walls are smooth enough. For particularly rough or otherwise non-reflective walls, cut the "+1 level" area in half.

[Ravingdork]

Light doesn't go around corners of opaque objects in real life. (Barring extreme gravitational pull or a nearby surface to reflect off of.) Why would it be different in game?

[kinevon]

Light would pretty much follow the rules for line of sight.

For your example, Paul, I would say that P would only be able to see that first square around the corner, and no further if he doesn't have either his own light source, or something like darkvision.

And the light would only go from the near corner between P and X to about 3-4 four feet into the corridor. In this case, as a GM, I would use a straight edge to check angles for it. I would probably be "nice" and use the top-left corner of the light source's square, and measure from there for line of effect.

[Arcanic Drake]

Actually, light does go around corners... just not by much (the reason why shadows are always fuzzy around the edges). Its one of the main reasons why we can't decide if light is a "wave" or a "particle," so we label it as both.

In this particular case though, we also have to consider the light "reflecting" down the corridor. All objects reflect a certain amount of light (which is how we see in the first place) except for "Dark Matter," which is so dark that is absorbs all light. I think Kazaan has the right idea because as the light source gets closer, less light is absorbed by the surrounding corridor and more is reflected into the adjacent one. The degree of this "Reflection" would also largely depend on how darkly colored the corridor's walls are (darker walls absorb more light, while lighter color ones absorb less) or if there are any actual "reflective" surfaces like mirrors or polished stone/jewels/metal/etc. within the corridor.

I'm not saying that it would light the corridor up like the actual light source was there... even a pure white wall "reflecting" light would make it... maybe three degrees less bright than the actual light source.

[littlehewy]

From a RAW point of view, I don't think there's a clear-cut answer. It's simply not addressed in the rules.

For practical playing purposes, it seems reasonable to allow some reflective bleed if the environment suggests it, as suggested above.

[Byakko]

pauljathome, the rules don't really cover lighting in great detail. Much of it is left to the GM's discretion. For the purposes of hiding and the like, it's generally safe to go with light not going around corners. However, it's ultimately a GM call.

Anyway, because I like science, let me clarify and/or correct some of the comments concerning light.

Quote:

Mechanical wise light does not travel around corners (though it does circle a globe which is why we get sunset sunrise.)

Light bends around the earth overwhelmingly because of refraction in the atmosphere. When light travels between materials of different densities, it will bend - this is often demonstrated with crystals and water. The earth's atmosphere is progressively less dense the higher you go, which causes light passing near the Earth to bend towards it.

However, this type of effect isn't going to be relevant for light traveling around corners in a dungeon, unless there's some very unusual gas density differentials going on.

Quote:

Actually, light does go around corners... just not by much (the reason why shadows are always fuzzy around the edges). Its one of the main reasons why we can't decide if light is a "wave" or a "particle," so we label it as both.

While there is a small amount of diffraction around the corners of objects, this is truly negligible in most situations. The distances involved are too small to have a visible effect unless extremely small alternating structures are involved. Further, because typical light is mixed spectrum, the differing amounts of diffraction from different wavelengths will diminish this effect still further.

The primary reason why shadows have fuzzy borders is because the source of the light is not a point. This means that in the fuzzy region of the shadow, only part of the light from the source is obscured by the object, causing a partial dimming.

Quote:

In this particular case though, we also have to consider the light "reflecting" down the corridor. All objects reflect a certain amount of light (which is how we see in the first place) except for "Dark Matter," which is so dark that is absorbs all light.

You may be confusing Black Holes and Dark Matter here. Let me cover both.

Black Holes aren't dark in the traditional sense that they are absorbing light. Light can reflect off particles beyond the event horizon just fine. However, due to the gravitational curvature of space, this light will never travel beyond the event horizon. (and even that isn't 100% true - it's theoretically possible for a particle of light to travel beyond the event horizon and almost immediately be outside of the event horizon again and able to escape, due to black hole shrinkage from Hawkings radiation)

Dark Matter, on the hand, is a poorly understood (and somewhat theoretical) form of matter which demonstrates its presence on a galactic scale by its gravitational effect. However, it's not called Dark Matter because it absorbs light, but because it doesn't interact with it (or other forms of matter) - light simply passed straight through it. This is why it can't be observed directly.

Because Science!

[Wheldrake]

It would be reasonable to allow a short distance of dim illumination around a corner from a light source like a lantern or sunrod. Candles and torches are already so dim that any additional illumination would be negligible.

How far would that "short distance" go? The RAW concerning lighting aren't detailed enough, so only a houserule can help. By RAW, it's line of sight only. But it would be reasonable to allow between 1/2 and 1/4 of the remaining illumination distance to exist down a side corridor (as dim light), depending on the relative darkness of the walls and environment.

[Just a Guess]

The question should be:
Is light an emanation or a spread effect?
The rules are silent on it but I would treat it as a spread because I think it fits better.

[Kazaan]

Just a Guess wrote:

The question should be:

Is light an emanation or a spread effect?
The rules are silent on it but I would treat it as a spread because I think it fits better.

It's neither, but somewhere in-between. As has been stated, the direct light from the source will not go significantly around the corner. You'll get a diagonal line into the first space into the corridor, but that's all the direct light that will enter the corridor. What we're talking about is indirect light. If you were sitting down a dark corridor as illustrated above, and someone were moving along the right-angle corridor with a light source, coming closer to the junction, you'd see, gradually, your dark corridor starts to light up a very little bit. The closer the light source gets, the more it lights up, but it isn't direct, normal-level light but rather indirect dim light. Once the light source hits the junction, then the full illumination radius will flood into your corridor. So it's "like" a spread, but not a full spread like a cloud spell. It's like an emanation, but not a full emanation because light is randomly bouncing off walls into the dark corridor.

[Just a Guess]

The game divides effects into th two, spread or emanation. So for the game it should be treated as one of those.
For reality it is a mix as you showed but the rules are no real life simulator.
So within the rules you have to choose one of the effect types. And, for me, spread makes more sense.

[Purple Dragon Knight]

Light does not bend around corners but it can reflect off surfaces. That is how we see. In game terms I'd say you get nothing around corner (i.e. pitch black around the corner. No dim lighting and nothing for low light characters. Keep the game simple if you want to optimize fun)

[Kazaan]

Just a Guess wrote:

The game divides effects into th two, spread or emanation. So for the game it should be treated as one of those.

For reality it is a mix as you showed but the rules are no real life simulator.
So within the rules you have to choose one of the effect types. And, for me, spread makes more sense.

False. The game divides AoE effects into three categories; Spread, Burst, and Emanation. The Light spell (and any derivatives thereof) is not an AoE spell despite affecting an area. It creates an effect and that effect is to change the light level. Furthermore, we're talking about light from both magical and mundane sources. You're mixing your apples with your oranges.

[Kayerloth]

mini rant:

And IMO they utterly botched it when they made all emanations 'bursts'. Emanation is more properly a state of duration not area (i.e. 'the effect continues') and Emanations themselves should be divided into Spread and Burst areas even if all the known current spells at that time happened to be burst emanations, ... sigh ...

[Arcanic Drake]

Byakko wrote:

Quote:

In this particular case though, we also have to consider the light "reflecting" down the corridor. All objects reflect a certain amount of light (which is how we see in the first place) except for "Dark Matter," which is so dark that is absorbs all light.

You may be confusing Black Holes and Dark Matter here. Let me cover both.

Black Holes aren't dark in the traditional sense that they are absorbing light. Light can reflect off particles beyond the event horizon just fine. However, due to the gravitational curvature of space, this light will never travel beyond the event horizon. (and even that isn't 100% true - it's theoretically possible for a particle of light to travel beyond the event horizon and almost immediately be outside of the event horizon again and able to escape, due to black hole shrinkage from Hawkings radiation)

Dark Matter, on the hand, is a poorly understood (and somewhat theoretical) form of matter which demonstrates its presence on a galactic scale by its gravitational effect. However, it's not called Dark Matter because it absorbs light, but because it doesn't interact with it (or other forms of matter) - light simply passed straight through it. This is why it can't be observed directly.

Hmm... Maybe I was confusing them... Actually I don't remember much of this post... I was really tired. Anyway, thanks for correcting me. I hate it when I give people misplaced or even wrong information...

[Kchaka]

First you need a real life light source that matches an ingame sunrod, something that will light a 60ft radious and beyond that is total darkness.

Now use this real 60ft radius light source in the real world corridor (or simulator), see how it illuminates the squares around the corner, and quantify the level of illumination into either normal light, dim light or darkness.

[kinevon]

Kchaka wrote:

First you need a real life light source that matches an ingame sunrod, something that will light a 60ft radious and beyond that is total darkness.

Now use this real 60ft radius light source in the real world corridor (or simulator), see how it illuminates the squares around the corner, and quantify the level of illumination into either normal light, dim light or darkness.

But you will also need to quantify a few variables in relation to the dungeon itself. The color of the walls, how reflective the walls are, along with some other things that can affect the light.