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View Full Version : [3.5] Do light sources stack?

Gaiwecoor
2010-07-04, 10:19 AM
As far as I'm aware, the question of stacking light sources isn't directly addressed in the rulebooks (I could be wrong here). How do you rule on this? If two shadowy illumination areas overlap, do they make a well-lit area?

I'm just looking for thoughts. I've seen it done both ways.

The Rose Dragon
2010-07-04, 10:21 AM
If two shadowy illumination areas overlap, do they make a well-lit area?

That would be weird. You could cast two darkness spells on top of each other and get a well-lit area.

Bharg
2010-07-04, 10:22 AM
Yes, they would stack, but I am not sure if that is a term of physics...

Rothen
2010-07-04, 10:23 AM
If there's no rulings, just go with common sense.

Two lamps close to each other don't make for a better lit area.

Fax Celestis
2010-07-04, 10:24 AM
If there's no rulings, just go with common sense.

Two lamps close to each other don't make for a better lit area.

...yes they do. Why else, when it gets dark, would you turn on more lights?

Bharg
2010-07-04, 10:24 AM
If there's no rulings, just go with common sense.

Two lamps close to each other don't make for a better lit area.

They do! But there a no ingame rules for that...

The Rose Dragon
2010-07-04, 10:25 AM
...yes they do. Why else, when it gets dark, would you turn on more lights?

Well, if you get two dimensionless sources of light and place them just right, you can get absolute darkness.

Aroka
2010-07-04, 10:25 AM
If there's no rulings, just go with common sense.

Two lamps close to each other don't make for a better lit area.

But the point is that the lamps aren't close to each other. This isn't two torches in adjacent squares, but rather two torches at, say, 70 feet apart. Both cast a 20 ft. radius of bright illumination, plus another 20 foot radius of shadowy illumination. That means the shadowy illuminations overlap. Does the area where both torches are casting light become bright illumination or stay shadowy illumination?

Bharg
2010-07-04, 10:27 AM
Well, if you get two dimensionless sources of light and place them just right, you can get absolute darkness.

Unlikely, but possible, I guess.

@Aroka: Use rules or common sense. Rules say nothing about it... Common sense says yes.

Snake-Aes
2010-07-04, 10:29 AM
But the point is that the lamps aren't close to each other. This isn't two torches in adjacent squares, but rather two torches at, say, 70 feet apart. Both cast a 20 ft. radius of bright illumination, plus another 20 foot radius of shadowy illumination. That means the shadowy illuminations overlap. Does the area where both torches are casting light become bright illumination or stay shadowy illumination?

I dare say they become well-lit. I don't know if there's a rule about that, but you're adding more energy to the system!

Hague
2010-07-04, 10:30 AM
That's really up to you. There's nothing that says they do but nothing that says they don't. I'd say if you have a natural light source, they stack but two magical ones don't.

I reckon they didn't add any rules because of how icky it would be differentiating between low-light and day vision and layering the light effects.

Rothen
2010-07-04, 10:36 AM
But the point is that the lamps aren't close to each other. This isn't two torches in adjacent squares, but rather two torches at, say, 70 feet apart. Both cast a 20 ft. radius of bright illumination, plus another 20 foot radius of shadowy illumination. That means the shadowy illuminations overlap. Does the area where both torches are casting light become bright illumination or stay shadowy illumination?

Yeah, sorry. I read it as "If my character holds two torches, can he see more?"

Heh, I was trying really hard not to facepalm.

Bharg
2010-07-04, 10:37 AM
That's really up to you. There's nothing that says they do but nothing that says they don't. I'd say if you have a natural light source, they stack but two magical ones don't.

I reckon they didn't add any rules because of how icky it would be differentiating between low-light and day vision and layering the light effects.

why would there be a difference between magical and non magical light sources as long as the magic isnt an illusion

2xMachina
2010-07-04, 11:24 AM
I think it should be stackable.

Each light source gives a lighting percentage. Full light is 100%. Shadowy is... less depending on how bright it is. Does not stack above 100%.

Say, a candle gives shadowy illumination. Does a lot of them give full light? I'd say yes.

Coidzor
2010-07-04, 01:52 PM
This calls for dwarven science.

BLiZme.2
2010-07-04, 01:55 PM
2xMachina's suggestions essentially what the candelabra rules in arms and equipment guide imply. You could look at that for any ideas on clustering (I agree overlapping shadowy arias create a bright area unless 1 is caused by a darkness spell then you get darkness)

Zaq
2010-07-04, 01:56 PM
That would be weird. You could cast two darkness spells on top of each other and get a well-lit area.

This makes me happy, or at least titillated, in a way I cannot quite put my finger on. I may use it if I ever make my "Shadowcaster who doesn't like darkness" character.

aje8
2010-07-04, 03:26 PM
Let's look at this from a physics perspective:

Ok, what perceive as light is actually large numbers of tiny particles called photons. Two lights would send out twice as many photons ergo the area would be twice as light. Actually.... it's a little bit more complicated than that as the lights send the photons in all directions and not automatically the same number in all directions....... but there still would be more photons in any given nearby area if not twice as many.

Thus, them stacking is probably the best approximation of what would actually occur.

I have no idea if the rules actually support that conclusion though........ never really came up in my games.

Rothen
2010-07-04, 03:33 PM
Ok, what perceive as light is actually large numbers of tiny particles called photons. Two lights would send out twice as many photons ergo the area would be twice as light. Actually.... it's a little bit more complicated than that as the lights send the photons in all directions and not automatically the same number in all directions....... but there still would be more photons in any given nearby area if not twice as many.

Do you have any kind of physics degree to back that explanation up? Because it seems to clash with my basic understanding of light and how it works. (ie: to me, it sounds like a lot of nonsense that you made up on the spot. :smalltongue: )

2xMachina
2010-07-04, 03:34 PM
Photons is supposed to be a light particle/wavelength.

Whether the theory is right or not...

Siosilvar
2010-07-04, 03:38 PM
Do you have any kind of physics degree to back that explanation up? Because it seems to clash with my basic understanding of light and how it works. (ie: to me, it sounds like a lot of nonsense that you made up on the spot. :smalltongue: )

He's correct, as far as I can tell from the chem/physics courses I've taken. Photon is a term used to describe an individual "packet" of light, as it behaves as both a particle and a wave at times.

Alternate/layman's explanation:

You put so much light in an area, it gets so bright. You put more, it gets brighter.

aje8
2010-07-04, 03:40 PM
Do you have any kind of physics degree to back that explanation up? Because it seems to clash with my basic understanding of light and how it works. (ie: to me, it sounds like a lot of nonsense that you made up on the spot. )
Well... the thing is...... it's actually a lot more complex than that because of something called particle/wave duality which basically means that light behaves like a particle and like a wave...... I have no interest however in going into my credentials or why this is true for a forum debate. I will admit, however, that that explanation was very much simplified.

EDIT: Ninja'd on the duality thing.

Aroka
2010-07-04, 03:44 PM
Do you have any kind of physics degree to back that explanation up? Because it seems to clash with my basic understanding of light and how it works. (ie: to me, it sounds like a lot of nonsense that you made up on the spot. :smalltongue: )

Can you give an alternate explanation?

retkin
2010-07-04, 03:59 PM
If you are letting the light sources stack, just have any 2 light sources with radius that overlap be fully lighten. Since you are already using some real world physics, sticking with the 100%/50% rule only is kinda silly, there would be many different levels of illumination, and the dead center where they exactly overlap wouldnt be any more brighter then a square or two to either side.

Claudius Maximus
2010-07-04, 04:02 PM
With this you could hold two torches and have the entire radius of light be considered bright light, and outside of that it is completely dark. How does that make sense?

nedz
2010-07-04, 04:56 PM
The darkness spell (assuming it were darkness rather than just some kind of pale insipid dimness) kind of throws physics out of the window. :smallcool:

Don't get me started on Darkvision.

I don't think discussing physics is relevent here.

The Rules are whats relevant here, only they seem to be silent on the issue.

Mastikator
2010-07-04, 05:08 PM
If you have one source of light and add one equal next to it, you've doubled the amount of light. So the light should now extend to the factor of the square root of two (~1.4) further.
So if the torch that lit up 30 ft was backed up by another torch it would now light 42 ft. And at the center the light would be twice as powerful, therefore well lit instead of poorly lit.

Morph Bark
2010-07-04, 05:14 PM
With this you could hold two torches and have the entire radius of light be considered bright light, and outside of that it is completely dark. How does that make sense?

Perhaps, rather than "stacking" in the sense that shadowy illumination + shadowy illumination = bright illumination, the "stacking" should be considered in the sense rather like critical multipliers and the like. Two or three light sources of equal power making the range of shadowy and bright illumination x1.5 as great as normal? Four to seven of them making it x2? Eight and more making it x2.5?

2010-07-04, 06:18 PM
"If my character holds two torches, can he see more?"
Well, maybe not by RAW, but obviously two torches provide more illumination than one in real life. Just like a single, brighter light source provides more illumination than a dimmer light source by producing more light. Why on Earth would increased light somehow not brighten an area more because it was being produced by two separate objects? I find that to be a bizarre and counterintuitive notion. Heck, how close to each other do you think that two light sources have to be before they somehow become redundant? :smallconfused: "Close" is a relative term, after all.

But, hey, you don't have to take my word for it. Try shining two flashlights on something in the dark if you're not convinced. Science! (http://xkcd.com/397/)

With this you could hold two torches and have the entire radius of light be considered bright light, and outside of that it is completely dark. How does that make sense?
Don't be ridiculous. Obviously, a torch sheds light beyond the edge of the shadowy illumination that it provides; that's why characters with low-light vision can still see (dimly) beyond that! And characters with superior low-light vision (like aquatic elves (http://www.d20srd.org/srd/monsters/elf.htm#aquaticElf)) can see farther still. And beyond that, even lower levels of lighting are still present. If one assumes that light behaves realistically, that is.

Plainly, a sensible implementation of this idea would involve increasing all of the relevant levels of lighting present, even those only implicit in the official figures given. Doy.

Edit: Let's say that, if a light source provides bright light out to a distance of D, then the level of illumination that it provides to points D away is 1. Then the level of illumination that it provides at a distance of R is D^2/R^2. (That's D squared divided by R squared.) The total level of illumination at a given point is the sum of the levels of illumination provided to it by all light sources. Characters without low-light vision perceive illumination of 1 or greater as bright, and illumination between 1/4 and 1 as shadowy. For characters with low-light vision, these figures are halved.