Light sources

[Dracorat]

Hello. As per an interesting discussion that came up, I need the following questions answered as RAW as we possibly can:

When a light illuminates "out to 20 feet, with shadowy illumination to 40 feet" how do we measure that, specifically? (I have always assumed accross intersections but now cannot seem to find a supporting rule)

What about vision that operates the same way? (Darkvision)

If the light is being supplied by a spell, is that different than light supplied by mundane methods in terms of valid points of origin (quest is coming up) and in terms of measurement method?

For large and larger creatures, if the point is an intersection, which ones are valid? Here is a large creature matrix to assist the answer:

A - B - C
| 1 | 2 |
D - E - F
| 3 | 4 |
G - H - I

Where numbers are squares they occupy and letters are board intersections.

And if you don't measure by intersection -- does that widen the resultant light template because they are wider than a single square? (I measure by intersections myself)

Finally, how often can something change the light's point of origin in relation to themself, what type of action is it and what are the limitations? Especially when we consider conal light sources - such as bull's eye lanterns.

Thanks for all answers. Sorry for the sheer number of questions.

Here are the questions in brief format for your convenience in answering:

Light - how it's measured --

Vision - works the same? --

Intersections - which are valid? --

Widening resultant light area of effect --

Ability to move light sources --

Action to move light sources --

 

[Felix]

I believe that the light emanating from the large creature would act in the same way that a mounted character acts on his horse; he's considered to be in every 5-ft square at the same time for purposes of reach and threatened areas.

So for your large creature, the light would extend 20 feet to the East of points C and I, 20 ft. South of points I and G, 20 ft West of points A and G, and 20 ft North of points A and C. Then connect the edges.

Shadowy Illumination extends in a similar manner, but goes 40 ft out from those points instead of 20, and starts where the clear illumination leaves off.

For folks with Low-light Vision, the clear illumination extends 40 ft instead of 20 ft, and the shadowy illumination extends to a radius of 80 ft.

---

For a medium sized creature occupying the square A-B-E-D, the light would extend 20 ft North, South, East and West from those points.

---

No, this does not render a Light spell that provides light in an area with a diameter of 40 ft, but rather 45, but this is done in the name of simplicity and conformity with the two principles that a spread spell effect is centered on a grid intersection, and that a character occupies the entire 5-ft square.

It makes light spells and darkness effects carried by a character slightly bigger, but it solves the problems created when you force them to choose an intersection. This is done for simplicity's sake and not realism.

---

Note that this means that if Light is cast upon a stone and carried, it will have a 45-ft diameter effect, but as soon as that stone is thrown, it will land on an intersection and thence have a 40-ft diameter effect; until picked back up, that is.

 

[Dracorat]

Thanks for the response, Felix. I can definitely see the simplicity with using the rules in the manner which you do.

Are there any RAW assertions for any of those or are they all how you do it yourself?

This is significant as I am involved in a project that will have to do light 'by the book'.

 

[Thanee]

Normally, you have to target an area spell on an intersection, however, light spells usually have objects as target, so that obviously doesn't work. So, if the illuminated area is figured like a spell area, I suppose you just designate one corner of the square, where the light source is located, to determine the area it covers. Area effects only work from intersections, so it needs to be an intersection, not a square.

In all honesty, I would just ignore that, though, and that's exactly what I do, and measure the distance from the square, as if you were moving or shooting to the target square, to see, if it is illuminated. It's not really an area effect spell, anyways, since it has no area entry in the spell description (at least Light and Daylight don't).

As for vision, you just check the distance as if you were moving or shooting to the target square. If it is within the limit (i.e. 60 ft. for standard darkvision), you can see, otherwise you cannot (or with penalties, depending on the situation).

Bye
Thanee

 

[Thanee]

This is significant as I am involved in a project that will have to do light 'by the book'.

I'm not aware of any rules, that detail this in any way.

As said above, the targeting rules for spells do not even apply, since light spells are no area spells.

Bye
Thanee

 

[frankthedm]

My gut feeling{and it is quite a gut]

Light source or anything with a specified radius, pick an intersection.

Darkvision and things that extend from a creature, count that may squares away in each direction.

 

[Felix]

Are there any RAW assertions for any of those or are they all how you do it yourself?

The rule assertions is that for area affects (while Light spells are not, they have an emanation effect). IE, the area of effect should be measured from a grid intersection.

However.

Because Light is cast upon an object, and this object can be wielded, I would then treat the lit area in a similar way I would treat a character's threatened area. After all, cast Light on a sword, would the origin of the light emanation stay in the South East corner when you attack the orc in the North West threatened square?

I wouldn't treat it exactly like threatened areas, otherwise casting light on a Longspear would result in a hugely lit area; I would confine the light effect to emanating from the corners of the square the character is occupying.

But if you're asking if this is RAW, I don't think it is, no.

 

[Infiniti2000]

Unfortunately, there are no rules establishing the exact point source for light like there are for spell effects. To make the world consistent when you cast area effect spells, however, it's better to just using the grid intersection as a guideline for lights (and darkness). The other problem with not doing this is that you need different templates for effects originating in a square vs. the well-defined ones for originating on grid intersections.

Light - how it's measured --
It originates at a grid intersection and the radial (and even cone) templates for that are pretty well defined.

Vision - works the same? --
The same thing. The creature picks a corner to measure from.

Intersections - which are valid? --
A creature holding a light source should be able to pick the grid intersection from the origin of the light source. A creature place a light source somewhere should be able to pick the grid intersection for the origin of the light source.

Widening resultant light area of effect --
If you do not set a grid intersection as an origin, then you need to decide what happens in the perimeter squares. They will be "half-filled". I would rule that as a lesser condition, if available, or nothing at all. In other words, the perimeter squares for light would be in shadows. The outer perimeter squares (normally shadowed) would be dark because there's just not enough light reaching that square to sufficiently illuminate it.

Ability to move light sources --
Yes. As I indicate above, I think you should be able to move the light source from one grid intersection to another (assuming it's not placed on a permanent object of course).

Action to move light sources --
Completely undefined, of course, but I'd say making it a free action is fine. It cannot be an immediate action IMO and a move action is just too much to what I feel basically amounts to a negligible shift in positioning.

 

[evilbob]

Personally I would always measure light sources that are held from the creature's square and not an intersection. For large creatures, this includes each square the creature occupies. I would also treat a dropped object as something occupying a square, but this could easily be done either way.

If you don't do it that way, you run into all kinds of annoying "facing"-esque issues that 3.5 generally tried real hard to stamp out. Down with facing! Held light-objects occupy all squares and directions!

Sorry: no RAW to back me up, though.

 

[Artoomis]

If you think about "Light" as having a range instead of a radius, it becomes easy. Treat it the same as a range weapon for deciding which squares it can reach.

Bottom line, start in a square, not a corner. If you try and switch corners around all the you'll go a bit stir crazy.

This works very well for meduim-sized creatures. For a large creatue (10'x10'), just use all four squares.

For bigger creatures than that, some DM judgement will be needed. No way around that.