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View Full Version : Darkvision, Infravision, Ultravision, Low-light vision



Random832
2009-07-09, 12:53 PM
EDIT: So... uh... thoughts?
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This is focused on d20/D&D, but can serve as an idea for other systems as well. "RAW" refers to 3.5SRD.

Required reading: Darkvision (http://www.dandwiki.com/wiki/SRD:Darkvision).
Recommended reading: Infravision and Why It Should Be Destroyed (http://www.seankreynolds.com/rpgfiles/rants/infravision.html).

Darkvision, as it is provided in RAW, cannot be an extraordinary ability (because it works in absolute darkness), yet it is.

Possible solutions:

Infravision
There are a number of problems with this. It does not plausibly have a distance limit, and some things should not be visible by it. The article I linked above explains in more detail, but the fundamental reason is: warm-blooded creatures (and fire, etc - anything hot) emit infrared light, and nothing else does (in any significant quantity above the background). Infrared sight cannot be a plausible explanation for the darkvision mechanic as written, and actually using it requires more bookkeeping. This is why it was removed. The distance limit, in particular, was based on the assumption that it would have similar resolution to 1970s-era infrared cameras, rather than being closer to the eye's resolution in detecting other light. There exists (http://forgottenrealms.wikia.com/wiki/Infravision) fluff implying infravision must be activated (which also makes no sense), but this isn't present in the 2nd edition rules texts available to me.

For the range limit, the basic problem with using infravision, even as fluff, is that a Red Dragon several hundred feet away is going to be emitting enough infrared light that it's totally implausible for you not to see it. Even ignoring the range limit, there is also the fact that the dungeon walls won't be emitting any infrared light.

Low-light vision
The problem with making "can see based on the little amount of light that is available" is simpler: low-light vision (http://www.dandwiki.com/wiki/SRD:Low-Light_Vision) already exists.

I'll note here It also doesn't make sense to have a hard distance restriction (though a change to what range you can spot things of a particular size at may or may not make sense). "See perfectly to 60 feet, then nothing" makes no sense as an extraordinary ability.

Generally, whether you can see an object should depend on the amount of light with which it is illuminated - a range limit on any vision ability - other than perhaps for being able to make out detail - only makes sense if you are carrying the light source. Which brings me to the final part of this:

Ultravision
This is proposed in a brief throwaway reference in the 2nd edition DMG. However, I realized that this is an almost perfect way to implement the darkvision mechanics as written. That is, with one change to the UV idea: characters with this form of ultravision emit UV light from their eyes. The advantage to this over doing the same with infrared is that creatures don't normally emit ultraviolet light as they do with infrared. The range restriction makes sense because the intensity of a non-laser light source diminishes the further away from it you are - at 60 feet out, objects are no longer sufficiently illuminated, the same as if you were using a small flashlight or a torch.

It lends itself to all sorts of optional mechanics, too, while still allowing the darkvision mechanic to be used unmodified with this as mere fluff if you so choose. Optionally, you could have this to require activation (they turn on and off their inner flashlight) rather than being always on... or not. For just a little more bookkeeping, you could extend the range restriction when more than one character with the ability is present (and looking in the same direction, if you really want to deal with facing). Glass blocks ultraviolet light - you could either include this as a limitation or say that it is not true of the glass used in your campaign world (maybe quartz crystals, like in Halogen bulbs, that don't filter UV, are used).

You'll note that I kept saying 'as an extraordinary ability'. The path not followed here is to simply redefine darkvision as being a supernatural ability. You should be able to figure out how to do that yourself - it is only a change of two letters in the right place, after all.

hiryuu
2009-07-10, 02:30 AM
Or you could check the entry for Extraordinary abilities.


Extraordinary Abilities (Ex)

Extraordinary abilities are nonmagical, though they may break the laws of physics. They are not something that just anyone can do or even learn to do without extensive training.

These abilities cannot be disrupted in combat, as spells can, and they generally do not provoke attacks of opportunity. Effects or areas that negate or disrupt magic have no effect on extraordinary abilities. They are not subject to dispelling, and they function normally in an antimagic field.

Using an extraordinary ability is usually not an action because most extraordinary abilities automatically happen in a reactive fashion. Those extraordinary abilities that are actions are standard actions unless otherwise noted.

Yora
2009-07-10, 05:06 AM
I see no reason, why darkvision shouldn't be based on IR-radiation or some similar fantasy-radiation to work.

Coidzor
2009-07-10, 05:44 AM
Background magical radiation FTW!

Eerie
2009-07-10, 07:44 AM
Background magical radiation FTW!

Or, better, background neutron radiation, and only magic prevents everyone from dying of cancer. :smallbiggrin:

PairO'Dice Lost
2009-07-10, 08:19 AM
Infravision
There are a number of problems with this. It does not plausibly have a distance limit, and some things should not be visible by it. The article I linked above explains in more detail, but the fundamental reason is: warm-blooded creatures (and fire, etc - anything hot) emit infrared light, and nothing else does (in any significant quantity above the background). Infrared sight cannot be a plausible explanation for the darkvision mechanic as written, and actually using it requires more bookkeeping. This is why it was removed. The distance limit, in particular, was based on the assumption that it would have similar resolution to 1970s-era infrared cameras, rather than being closer to the eye's resolution in detecting other light. There exists (http://forgottenrealms.wikia.com/wiki/Infravision) fluff implying infravision must be activated (which also makes no sense), but this isn't present in the 2nd edition rules texts available to me.

For the range limit, the basic problem with using infravision, even as fluff, is that a Red Dragon several hundred feet away is going to be emitting enough infrared light that it's totally implausible for you not to see it. Even ignoring the range limit, there is also the fact that the dungeon walls won't be emitting any infrared light.

I introduced a homebrew race with infravision into one of my games, to see if I could get infravision to work plausibly. Here's how I handled it:

1) Range limit: There's no range limit on infravision; instead, you can see things that give off heat based on their size, doubling it for fire creatures or other really hot things and halving it for colder-than-normal things, as well as doubling or halving based on the background temperature--seeing a great red wyrm in the arctic is trivially easy, a mouse in the desert not so much. You only see these hot things, not walls and floors and such.

2) Infravision modes: In addition to "passive infravision" that works like 1 above, you can go to "active infravision" as a move action. This version is magical and is essentially infravision radar (as you suggested for ultravision)--you can see things that aren't already heated, but you detect on infravision as a hot creature two size categories larger. Using either mode of infravision in daylight dazzles you, and a fire effect disrupts infravision to varying degrees (no pun intended) for as long as it lasts (or until the end of the user's turn, for Instantaneous stuff).

3) Miscellaneous: Infravision users gain bonuses when tracking creatures that give off heat, spot bonuses against creatures hiding with concealment rather than cover, and a few other things.

4) Magic: Spells work on infravision as well--spells deal with the entire EM spectrum, so invisibility hides all EM radiation, including light and IR (though your tracks can be detected, just like you could find an invisible creature if he steps in a puddle), illusions have heat signatures of the creatures they're mimicking, magical darkness isn't "darkness" but an area devoid of nonmagical EM radiation, etc.


Using these 4 rules required only a few tweaks and seemed to work out well for us without breaking verisimilitude or causing balance problems. It's probably more work than it's really worth, honestly, but if you like having an explanation for darkvision past "you magically see in the dark (but it's actually nonmagical)" I think it's worth it.

Random832
2009-07-10, 09:55 AM
Using either mode of infravision in daylight dazzles you,

Why? Sure, the sun's hot, but it's also bright; that's why we don't look directly at it.

PairO'Dice Lost
2009-07-10, 10:31 AM
Why? Sure, the sun's hot, but it's also bright; that's why we don't look directly at it.

To go along with some subterranean races' Light Sensitivity or Light Blindness traits. Since most races that have those traits now had infravision in prior editions, it provides a bit of continuity.

The basic idea is that eyes adapted for infravision are more sensitive and thus sopmewhat overwhelmed by normal light. When I said "using infravision in daylight" I probably should have been clearer--if you have passive infravision, it's still "on" when in normal light, so that sentence should probably read "If you have infravision, daylight dazzles you, but there is no extra penalty for using active infravision in daylight." Makes sense?

Solaris
2009-07-11, 10:47 PM
Infravision
There are a number of problems with this. It does not plausibly have a distance limit, and some things should not be visible by it. The article I linked above explains in more detail, but the fundamental reason is: warm-blooded creatures (and fire, etc - anything hot) emit infrared light, and nothing else does (in any significant quantity above the background).

Eh. I've used Thermals an awful lot, and I've yet to encounter something you couldn't see with IR. You can't look through glass, but that's about the only real hindrance. (Most anything else also obstructs visible light). In short, with high-res thermal imaging you can see monochrome, but you'll be picking out critters a lot easier. You can see lizards pretty good, too, if you've got the gain set properly. They're a coupla degrees above the environment. Cold critters show up, as they'll be much darker than the environment.
I've never understood why people thought it'd be so hard to use infravision when it's really just something along the lines of "You have darkvision, range unlimited (because it's part of your vision, natch) with a bonus to Spot things in the dark/with concealment based on temp, see below table."
And then the table's something to the effect of:
+/- 5 degrees above the environment - +1
+/- 11-15 degrees +2
+/- 16-50 degrees +4
+/- 51-100 degrees +8
+/- 101+ degrees +10

To go with what Pair O' Dice said.