Infravision & Your Fantasy Hero
by Roger E. Moore
(C)1995 TSR, Inc. All Rights Reserved.
This article first appeared in DRAGON(R) issue #211 (Nov. 1994) as 
"Sight in the Darkness"; this file updates and corrects the 
earlier article.

    What would it be like to see in the dark?
    My interest in this topic was sparked years ago when I tried 
to figure out just what my half-orc AD&D(R) game characters could 
see using infravision in a dungeon. I wanted every advantage there 
was for those obnoxious little guys. Additionally, I wanted to 
know just how well infravision-using monsters could see in the 
dark, because I wanted my characters to avoid being seen and 
promptly eaten, as a number of them were.
    This interest was sparked again recently by an article in a 
science magazine on infrared vision. Some very intriguing points 
came to light, and the results are offered here in the hopes that 
AD&D and D&D(R) game players everywhere will find them useful. 
(Certainly, my half-orcs would have gotten a longer leash on life 
with this information.)

How infravision "works"

    We should really start with a look at real-world infrared 
light and infravision. This makes certain game aspects of this 
sensory power clearer, and also highlights inaccurate, 
contradictory, and problematic aspects of infravision in game play 
(which will be discussed in depth later).
    The science article that fired me up for this topic was 
"Seeing the World Through Infrared Eyes," by Neil F. Comins 
(Astronomy Magazine, June 1991, pages 50-55). This excellent 
piece covers the basics of how infravision would work in realistic 
terms. It's worth hunting for this article in your local library 
and copying it for reference. That and a few encyclopedic entries 
are the basis for the information that follows.
    Infrared radiation is normally invisible, lying just below red 
on the electromagnetic spectrum. It is given off by hot objects; 
the hotter the object, the more infrared light it gives off. Very 
hot objects eventually give off visible light--red light at first, 
then orange, yellow, and white as the heat increases. We can sense 
heat radiation on our skin, the largest sensory organ we have, but 
we cannot detect more than a general direction of the heat source 
and an idea of how hot the source must be.
    Certain snakes called pit vipers are able to detect infrared 
light more accurately than we can, though only within a short 
range. Several sense organs called pit organs lie to either side 
of a pit viper's head, between the eye and nostril. Changes in 
heat radiation as little as 1 degree can be detected. The snake 
senses the direction of the heat source by moving its head back 
and forth, noting the direction and intensity of the heat it 
senses.
    We've known about heat for eons, but infrared light itself was 
discovered by an English astronomer, Sir William Herschel, in 
1800. A very practical use for infrared light was found during 
World War II, when electric sniperscopes were invented. 
Sniperscopes were attached to rifles and gathered distant infrared 
light coming from the bodies of soldiers, converting it to visible 
light for the sharpshooter. This allowed sharpshooters to fire on 
enemy positions at night. (As will become apparent, some versions 
of infravision in the AD&D game were based on sniperscope 
characteristics.)
    Infrared light has less energy than visible light, but it 
behaves in much the same way. Some infrared radiation is absorbed 
by molecules in the air. However, near-infrared light, which is 
the part of the infrared spectrum closest to visible red light, is 
reflected by most objects and thus can be used to detect them. We 
see a chair by the light reflected from it; a pit viper can detect 
nearby objects by the near-infrared heat reflected or emitted from 
them.
    Our ability to actually see infrared heat in detail is blocked 
by several major problems. Because infrared light is less 
energetic than visible light, a human able to see near-infrared 
light clearly would need eyes about 5-10 times larger than normal. 
Worse, heat is emitted from many objects all around us; stoves, 
furnaces, living beings, light bulbs, hot car engines, and 
sun-warmed rocks, concrete, bricks, and asphalt for example. 
Almost everything with any warmth would glow as if it were a light 
bulb, though with an intensity proportionate to how hot it was. 
Thus, an oven will be "brighter" than a warm rock.
    What this means, of course, is that anyone able to see 
infrared light also will see his own body warmth. We have body 
temperatures just below 100 degrees F., which is enough to blind 
us with heat radiation. It's like trying to take a picture when 
the camera itself emits light inside and out, ruining the film.
    To prevent such heat blindness, an infravision-using creature 
would need some sort of insulation around its eyeballs to keep the 
body's heat out of them, and some kind of refrigerant to keep the 
eyeballs cool so they become sensitive to outside light. This 
insulation and refrigeration would be done biologically. (Don't 
ask me exactly how, but I'm sure Mother Nature would figure out a 
way.) However, let's face it: We're dealing with magic, not 
science, and magic can do anything. Our problems are solved at a 
stroke, even if it doesn't please the scientists among us.
    Another option--useful for beholders, giant snails, and 
crabs--is to put the eyeballs on stalks, separating them from the 
rest of the body. The eyes are thus air cooled, so no other 
refrigerant is needed. I don't think beholders and so forth have 
infravision, though (as is noted later) if they've lived 
underground for a long time, they've probably developed it.
    In some ways, the way that infravision is described in the 
AD&D game rules implies that it works in the same way that our 
night vision normally works. Rod-shaped cells in the retina of 
your eyes can detect very dim light after a short period of 
adjustment to darkness, which you should be familiar with each 
time you go into a dark room. At first you can't see a thing, but 
over a period of minutes you start to see more and more objects in 
what little light there is. Eventually, faint light sources like 
the full moon, digital clocks, and even pure starlight can seem 
quite bright, even painfully so. However, because rod cells are 
not color-sensitive like the eye's cone cells, night vision is 
mostly black-and-white vision; maybe "shades of gray" vision is 
more accurate. (Infravision was described as being like 
black-and-white vision in the original AD&D game, too, as noted 
later.)
    Night vision can be instantly spoiled by bright normal light, 
which is why driving experts tell you to look away from oncoming 
cars at night, to preserve your eyes' sensitivity. Infravision in 
the AD&D game is spoiled by bright visible light, extremely hot 
objects like fires, and magical light. Perhaps fantasy creatures 
with infravision have magical cells in their eyes that work like 
rods, but pick up heat instead of faint visible light. Who knows?
    So much for how infravision works. What can you see with it?

The infravisual world: Aboveground

    We'll assume that your campaign world resembles our own Earth 
in that it has a normal day-night cycle with a sun like our own. 
(If this is not the case, you can make adjustments as we go 
along.) What would your heat/infrared picture of the world look 
like, then? Let's use some logic as we look around.
    In the daytime in summer, everything bathed in sunlight is 
warm. Things that retain heat well, like large rocks, will be 
warmer and stay warmer longer than things that lose heat rapidly 
in cool winds, like thin leaves or blades of grass. The greatest 
normal heat source is the sun, which we can easily assume is too 
bright to look at with any form of infravision. Sunlight in fact 
ruins AD&D game infravision, so we would rely on normal vision 
alone. Air is assumed to be invisible, whatever its temperature, 
unless it is extremely hot (see below).
    So infravision is useless in broad daylight. Once darkness 
falls, however, the landscape is still hot. Objects retain heat 
from the sun and radiate it slowly away, which keeps the night 
side of the world from freezing. (Even magical worlds need 
thermodynamic physics!) With the sun gone, a creature with very 
good infravision could see almost normally right after full 
darkness falls, since the terrain will radiate light. We can 
assume that a combination of rod-based night vision and 
magic-based infravision would be a potent mix, allowing vision 
about equal to normal sight in full daylight. Distant images would 
be fuzzier and less distinct than usual, so a far-away orc might 
look like an ogre or a halfling, but it beats seeing nothing at 
all.
    Different parts of the landscape will cool off at different 
rates, so things will look strange. Rocks would be "brighter" than 
trees, for instance. Water is generally cooler than land, but 
water also retains heat better than land; thus lakes and seas 
might seem "brighter" than the shoreline, especially late at 
night. Very hot air, such as that escaping from chimneys or fires, 
will glow faintly like a luminescent cloud.
    Other warm things in the world include live animals, 
especially the warm-blooded ones, and fire. A deer, a human, and a 
chipmunk all radiate heat--more heat when they are ill or 
physically exerting themselves, less heat when standing still or 
asleep. Certain magical animals, such as salamanders and red 
dragons, can be assumed to produce much more heat than other 
creatures their size. I recall reading that drinking alcohol 
causes the body to radiate more heat than usual, so a drunkard 
could be detected by being "brighter" than other people.
    Objects in close contact with living beings, like clothing, 
weapons, tools, chairs, and beds, will radiate some heat after the 
beings leave or discard them. In time, of course, those objects 
will completely cool off. Standing on a spot or leaning against a 
wall for a while also will leave residual heat behind, which could 
be noticed. Scuffing or shuffling feet would leave infrared 
"footprints" that could be tracked, though not for long. Friction 
from dragged objects, like heavy sacks or combat victims, also 
could be detected, as could places where surfaces have been rubbed 
together for long periods of time (machine gears, gristmill 
stones, axle joints, spinning wheels, etc.). Physical blows, like 
being smacked with an open hand or a blacksmith's hammer, also 
raise the temperature of solid surfaces for short periods of time.
    Fires produce vastly more heat than living beings. Seeing a 
living being hiding next to a blast furnace in a dark room would 
be almost impossible, like seeing a firefly's light next to the 
sun's. Manmade and natural sources of fire include matches, pipes, 
cigars, candles, torches, campfires, bonfires, hearths, furnaces, 
forest fires, lava, and embers. All flame sources are assumed to 
emit enough infrared and visible light to ruin infravision near 
them. Note however, that a "dead" fire would radiate heat long 
after the last ember has vanished, and likely would be detectable 
at a great distance. A forest fire would "light up" the landscape 
for many hours after the flames are gone.
    Remember, too, that infravision also detects the lack of heat, 
just as normal vision detects the lack of light. Snow and ice will 
look very dark in infravision if seen without visual light from 
moons or stars. A cold-producing object like a refrigerator also 
will look darker than objects around it. Cold-producing creatures 
like brown mold or a lich (whose frosty touch causes frostbite 
damage) will look very "black."
    It's worth a word on what sorts of creatures could not be seen 
with infravision. Creatures that are normally able to turn 
invisible, like pixies, should also be invisible to infravision 
but not to other senses like smell. Any creature that is roughly 
the same temperature as its surroundings, like a cold-blooded 
insect, fish, amphibian, or reptile, would be harder to see at 
night, though even cold-blooded creatures aren't always exactly 
the same temperature as the environment around them. (Live things 
move and so generate friction from moving, for one thing.) Magical 
beings that radiate no heat at all, like undead skeletons and 
zombies, would be almost invisible to infravision unless revealed 
by reflected infrared light or else blocking a much hotter source, 
revealing their outline.
    With so many heat sources at night, and so many things that 
will reflect infrared light, there will be a multitude of 
infrared-light shadows. The landscape will lack clarity and seem a 
bit out of focus (even more so at greater distances), as well as 
painted in shades of gray. It's a confusing, alien world, but any 
creature born with infravision would be quite accustomed to it and 
might instantly recognize any critical feature it sees.
    Neil Comins' article notes that the night sky itself would 
change when seen through infravision, but modern-world astronomy 
is considerably different from the AD&D game's SPELLJAMMER(R) 
setting "physics." In essence, any heat source in wildspace will 
glow fuzzily in infravision, but it's up to the Dungeon Master to 
choose which things seen in the night sky are heat-emitters and 
which are not.
    Stars, for instance, might radiate only visible light and no 
heat at all, thus being invisible in infravision but not to normal 
or night vision. Fire bodies, like suns, will certainly emit 
enormous amounts of heat and be easily visible from a planet's 
surface as enormous, brilliant, fuzzy balls in the sky. Air bodies 
will emit or reflect very little heat (becoming invisible), and 
earth and water bodies will only reflect heat (being barely 
visible unless they are close to a heat source).
    Let's take three well-known crystal spheres and see what's to 
be seen in the infravisual sky. Oerth, home of the GREYHAWK(R) 
campaign, is set in Greyspace (described in the SPELLJAMMER 
accessory SJR6 Greyspace). The local sun, Liga, is an enormous 
fire body that will temporarily blind any infravision-using 
creature dumb enough to look directly at it. Oerth's two 
moons--Luna (a.k.a. Raenei) and Celene (a.k.a. Kule)--shine 
clearly by reflected infrared light from Liga, passing through 
normal lunar phases. Other planets are much farther away and thus 
much fainter, though some have their own heat source, like the air 
world, Edill (which has small fire bodies within it). Stars in 
Greyspace are actually gigantic gemstones set in the crystal 
sphere itself that emit light but no heat, thus being invisible to 
infravision.
    Krynnspace, home of the DRAGONLANCE(R) setting, has two fire 
bodies: the sun and Sirion, the small innermost planet. The sun, 
of course, is staggering bright (just like Liga, above, or our own 
Sun). Infravision makes Sirion look like the second-brightest body 
in the sky, however, as it gives off so much more heat than any 
other planet. Reorx, an earth body that is the second planet out 
from the sun, is third brightest; it reflects heat from both the 
sun and Sirion, which often appear widely separated when seen from 
Krynn. Krynn's three moons also reflect heat from both sources, 
becoming the fourth, fifth, and sixth brightest bodies. Outer 
planets reflect less light and are thus dimmer in Krynn 
"infra-sky." The stars here, as in Greyspace, are invisible to 
infravision, emitting only light from the quasi-elemental plane of 
Radiance. DMs should read SJR7 Krynnspace for more.
    Finally, from the justly famed surface of Toril (home of the 
FORGOTTEN REALMS(R), Kara-Tur, Horde, Maztica, AL-QADIM(R), and 
MALATRA(TM) settings), the sun is the dominant object in the 
"infra-sky." It is interesting to note that Coliar, the second 
planet out from the sun, is almost invisible because it is an air 
body; the sun's heat goes right through it. However, because of 
the small "islands" of rock circling within Coliar, infravision 
might show the planet to actually be a spherical collection of 
pinpoints of light, reflecting heat from the sun. Selune (Toril's 
great moon) and the Tears of Selune (a cluster of asteroidal 
bodies circling Selune's trailing Lagrange point) shine clearly by 
reflected heat from the sun, when seen from Toril. Other worlds 
appear very faint, with the exception of Anadia, an earth body and 
the closest world to the sun, and Garden, which is illuminated by 
one of its moons, Sunson, a miniature fire body. Garden's other 
moons might also show up clearly in infravision through a 
telescope, reflecting Sunson's heat and light. Again, the stars 
are infra-invisible. See SJR2 Realmspace for more.
   Given the above settings, you can see that even when the sun 
goes down at night, infravision might still reveal a great deal 
about the surface world if a heat source is still in the sky. 
Garden's Sunson might be bright enough infravisually to cast 
shadows at night on Toril, like a full Moon on our Earth. This 
would be especially true when Garden is in conjunction with Toril 
(i.e., when it is closest to Toril). Sirion would appear from 
Krynn to be an extremely bright "morning star" or "evening star" 
(in the manner of Mercury or Venus, as seen from Earth), but it 
would also reveal the local landscape quite clearly.
   Collisions between celestial bodies will produce brief bursts 
of infrared light (heat). As asteroids in the Grinder of Greyspace 
or earth bodies within Krynnspace's air-body Zivilyn collide, an 
infravision user elsewhere in local wildspace would see a brief 
burst of bright light that fades away rapidly.
   If a DM is designing an original campaign world using a 
completely different astronomical set-up, he can use logic and the 
above examples in designing the "infra-sky" of his world. What 
about an air body full of nonluminous but very hot gases? A cold 
air world that eclipses the sun, not reducing visible light but 
cutting down heat radiation briefly?
   You might also consider creating a large selection of 
infravision-using monsters on your world, with behavioral patterns 
that vary according to the heat-brightness of the sky. Carnivores, 
especially, will be more active when they can see clearly.

The infravisual world: Underground

    Infravision is remarkable enough to surface-dwelling 
creatures. Let's look at what it's like for subterranean beings, 
and what advantages and disadvantages they gain from it.
    In our real world, deep caverns tend to have a uniformly cool 
temperature; Mammoth Cave, in central Kentucky, has an average 
temperature of 54 degrees F. that varies only slightly year-round. 
This coolness makes everything look the same, bland shade of gray 
to an infravision user, but there is plenty of hope here for 
diversity. For one thing, large openings radiate only faint heat 
(from objects beyond them), so such openings will look dark. More 
distant objects radiate less visible heat than closer ones, so 
distant objects are dimmer and darker. You could thus pick out the 
shape and direction of an unused tunnel with little trouble.
    Running water underground is often extremely cold, so cave 
water will seem very black, as will the rocks surrounding it. If a 
cavern complex is near a geothermal heat source, like a geyser or 
(heavens forbid) volcanic magma, the entire cavern will grow 
warmer and "brighter" as an infravision-user gets closer to the 
heat source.
    Caves often have a variety of life in them, especially in 
fantasy worlds, and living beings will radiate enough heat to 
"infra-illuminate" their surroundings. The more beings, the 
brighter their living space; a thousand goblins should be able to 
see their underground lair quite clearly with no other "light" 
than the heat from their own crowded bodies.
    Heat-producing magical creatures, like red dragons, will of 
course radiate vast amounts of infrared light. A red dragon would 
have an advantage, too, in that one short puff of flame will ruin 
the infravision of any approaching creature, with fatal results 
for the blinded ambushers. Some cold-blooded creatures like 
slithering trackers would be invisible to infravision, again with 
fatal results for cocky adventurers. The special dangers of 
skeletons, clay golems, and other "heatless" monsters becomes 
highly apparent.
    Some undead, however, radiate cold. Liches, for instance, 
cause damage from their chilly touch; they and their hands should 
"glow black" in infravision, standing out against warmer 
backgrounds, even cave walls. Read the descriptions of monsters 
carefully if you want to produce a more detailed and intriguing 
picture of underworld life to adventuring dwarves, gnomes, and 
elves.
    Speaking of fantasy races, a short history of infravision, as 
it appears in TSR's fantasy games, is in order.

Infravision and the AD&D game

    References to infravision are scattered throughout the AD&D 
and D&D game rules, but it becomes obvious that the concept 
underwent much expansion and refinement over the years since 
either game first appeared. It would help to start out with a look 
at what infravision used to do in fantasy games, and what it does 
now--as well as collect the rules on infravision together in one 
spot for ease of reference. A few areas of omission and 
contradictions that have confused the playing of infravision will 
become apparent.
    Certain races in the Chainmail rules (the war-gaming rules 
from which role-playing sprang) were able to "see well in dimness 
or dark." Dwarves, gnomes, goblins, kobolds, and orcs, as 
subterranean races, needed the ability to get around in caves and 
mines when candles and oil lanterns weren't available. If you 
dumped the infravision concept entirely, this sort of vision could 
be either light-intensifying vision, making the most of every 
visible-light photon in the area, or a form of magical radar, 
allowing for an accurate map of local surroundings without 
recognition of color or "flat" things like paintings, handwriting, 
etc. It could even be magical vision that makes dark areas seem to 
be lit by sourceless light, so there are no shadows (color is 
optional). Take your pick.
    Hard on the Chainmail game's heels in 1974 came the D&D 
Original Set, those three tan booklets in the white box. There, 
the infravision spell first appeared. The original version of 
the spell allowed the user to "see infra-red light waves, thus 
enabling him to see in total darkness." (Of course, you still 
might not see in total darkness if there were no heat sources 
around.) The spell lasted for one day and had a range of 40-60 
feet. Interestingly, it wasn't until a later D&D supplement 
appeared (the Greyhawk book) that dwarves, gnomes, and elves 
were noted as having infravision allowing them to see monsters up 
to 60 feet away in the dark. (Elves were probably allowed this so 
they could see at night, though light-intensifying vision would 
have been more logical.)
    The original AD&D game's Player's Handbook and assorted 
monster descriptions gave infravision to many creatures, including 
every demihuman PC race except certain halflings. Different types 
of infravision began to appear, too, defined by range. Poor 
infravision was effective only out to 30 feet, and was found in 
certain halflings and derro, an evil dwarflike race. Normal or 
standard infravision, good out to 60 feet, was the most common 
variety. Superior infravision extended out to 90 feet, as was the 
case with trolls and troglodytes, or 120 feet, for drow and 
duergar (evil dwarves). In one place (page 102), the Player's 
Handbook says that monsters living in dungeons have infravision 
out to 120 feet; why then do some have shorter ranges? Hmmm.
    Superior infravision, however, involved more than simply 
receiving heat radiation. Creatures with long-distance infravision 
were noted in the 1st Edition DUNGEON MASTER(R) Guide (page 59) 
as emitting infrared light from their eyes (magically, of course), 
then seeing the reflected radiation. (This would not be possible 
in normal science, as noted earlier, but this is a magical 
universe we're talking about.) The eyes of any creature with 
infravision out to 90 feet or more are noted as glowing red quite 
brightly when seen by any other creature with standard 
infravision. Most monsters in underground areas were said to have 
superior infravision.
    This brings up a curious point: How far away can an adventurer 
with standard infravision detect one with superior infravision? 
Can the adventurer see danger coming before the dangerous creature 
sees him? Well, if you get picky about it, you can say that the 
standard range of 60 feet is fixed; you can't see farther than 
that, no matter what heat source is out there. On the other hand, 
it is clear that the original intent of the rules was to have the 
60 feet range be that at which the body-heat radiation from 
monsters (and normal people) could be seen. The implication is 
that stronger sources of infrared light could be seen if they were 
farther away.
    A liberal DM should note that a creature with 90 feet or 120 
feet infravision is actually emitting infrared beams out to 180 
feet or 240 feet, respectively. All infrared light going out from 
its eyes must be reflected back to its eyes to be seen, so in 
theory those eye beams should be detectable by infravision out to 
those doubled ranges (assuming those eye beams don't first 
encounter a surface that causes them to be reflected). 
Furthermore, near-infrared light reflects from most normal 
surfaces just like normal light. A monster with superior 
infravision "paints" everything it sees with powerful heat rays, 
just as if it were carrying a double-beam flashlight. (Perhaps 
dwarves and gnomes have appropriate expressions like, "That troll 
was so close that its eyes could've burned the skin off my arm!")
    Thus, a gnome wandering an abandoned mine tunnel might see the 
corridor ahead of her "light up" with faint infrared light if 
there was a duergar 240 feet ahead of her. The duergar has the 
advantage in having a much broader range of accurate vision, but 
the gnome has the advantage of early detection. The gnome can 
immediately flee or hide, unseen by the approaching duergar.
    This argument is buttressed (and contradicted) by the note in 
the original DMG (page 59) that, outdoors, infravision allows 
for detection of warm or cold figures at a range of 100-300 feet. 
Vision is said to otherwise be equal to "a bright, starry night, 
with full moonlight." Cannot the duergar then see the gnome at 240 
feet? What heat sources are present that allow for this greater 
range of vision? And if you can see up to 300 feet outdoors, why 
can't you see that far indoors? Game logic breaks down at this 
point.
    To the rescue, perhaps, comes the earlier notes about a 
sun-warmed landscape and rod-based night vision. As a rule of 
thumb, let's say that a creature with infravision can see three 
times as far outdoors at night as it can in a deep cavern, because 
the landscape is warmer and radiates more infrared light. A 
halfling with poor infravision thus can see most outdoor objects 
out to 90 feet, and a duergar (with infrared eye beams) can see 
out to 360 feet. The gnome in the earlier example should obviously 
avoid meeting duergar at night in open fields; the duergar will 
see the gnome first.
    In the original PHB (page 102), things seen with infravision 
are described as appearing in a colorless way to an observer. Warm 
things look bright, as if they were emitting light. Cooler things 
look progressively more gray, and cold things appear black. This 
fits with the black-and-white view of infravision developed 
earlier. Recent versions of the D&D game have instead substituted 
certain colors for different heat temperatures (D&D Cyclopedia, 
pages 24-25), and there is that nagging PHB note about the 
red-glowing eyes of a creature with superior infravision. The 
optional rules for infravision in the AD&D 2nd Edition game DMG 
(page 119) also allow for "pseudo-color" infravision, as typically 
appears in a thermogram. I'll still opt for the simpler no-color 
view, which makes it just like the view you get from a 
sniperscope.
    Does infravision work underwater? Yes, but badly. Water is a 
very poor conductor of heat, despite what any game rules say. 
Though the original DMG allowed infravision to work underwater 
to a limited extent, but it would be more accurate to cut it off 
completely. Cool water will dampen out nearly all heat radiation, 
and warm water will obscure it. I'm no scientist, but I'd give 
infravision an underwater range of about 1 feet, no more. Very hot 
sources, like a volcanic vent, will boil all the water near them 
and make an infravisual view of them merely bright, fuzzy blobs 
that fill your field of vision. If you are liberal, you can keep 
the limits set by the original or AD&D 2nd Edition rules (i.e., 
normal underground ranges).

Getting clever with infravision

    What new tricks can infravision bring to a typical AD&D game? 
Here are some possibilities: 
    Given that infravision is not as precise and focused as normal 
vision, the chances for mistaken identity increase when only 
infravision is used. An orc at a distance looks like a human or a 
hobgoblin; long experience and closer inspection (at great risk) 
will tell the difference. DMs should play up on this at every 
opportunity.
    As a rule of thumb, a DM could say that accurate 
identification of a creature can be made using infravision only 
when the target being is one-third the distance of the spotter's 
infravision range. Thus, a dwarf can accurately identify a comrade 
at a range of 20 feet (one-third of 60 feet), and a duergar can 
identify a fellow monster at a distance of 40 feet.
    Can you read by reflected infrared light, if no normal light 
is present? For the record, we will assume not, unless the heat 
source is very strong and the writing is only inches from one's 
eyes.
    Thieves with infravision can learn to hide themselves from 
other creatures with the same power. A very powerful, blinding 
source of heat or the presence of many separate, man-sized sources 
of heat (like a group of bodies immediately after a battle) can 
conceal the thief's presence quite well. However, simply hiding 
behind a rock is no help at all, as the thief's own heat radiation 
will be seen around the rock's edges and "painted" over background 
objects. Wrapping up in a blanket might help at first, but the 
blanket will slowly grow warmer (and brighter). Hiding against a 
cold object will make the warmer thief stand out as if he were in 
a spotlight. If you are playing a thief (as a player or DM), 
imagine that character as a permanent, glowing light source. How 
can you hide that light? Magical invisibility might be the only 
foolproof recourse--but even that can be challenged by creatures 
with superb senses of hearing or smell.
    The descriptions of monsters should be carefully examined to 
determine if any being might radiate more or less than the "usual" 
amount of heat. Considerable leeway is given for the DM here. A 
dragon turtle, which breathes steam, and a remorhaz, which is 
incredibly hot, are likely to put out enormous amounts of infrared 
light. What about a flametongue long sword or a necklace of 
missiles? Though it is tempting to rule otherwise, magical items 
might not put out any heat at all, no matter what their powers, 
unless the description of them in the DMG says they do.
    Consider the infravisual effects of certain spells. Fireball 
will produce a burst of infrared light that will temporarily blind 
any creature totally dependent on infravision. Incendiary cloud 
is easily distinguished from all other cloud-type spells because 
the cloud radiates so much heat that it glows brightly in 
infravision. Burning hands could briefly illuminate a large area 
like a flash bulb, if the infravision users had their backs to the 
spell effect so they weren't blinded by it. Dancing lights, 
which radiates no heat, could be instantly told apart from real 
torchlight by infravision users. Chill touch makes the user's 
hand seem black (cold) in infravision. Use your imagination with a 
careful touch of logic and reason for other spells.
    Everything that a dwarf knows about infravision is likely 
known by a goblin, and vice versa. Creatures who have no 
infravision are more likely to fall for certain traps set by those 
who can see heat. For instance, a goblin stonework trap that was 
recently used or tested will be visible to a dwarf, who can detect 
the heat from the friction of stones sliding across each other. An 
ambush site will radiate enormous heat from the bodies of the 
gathered ambushers, tipping off other experienced dark-dwellers. A 
tank of cold water, set over a thin, wooden ceiling, will made the 
area around it very dark. A corridor recently hit by a fireball 
spell will radiate much heat (and probably smell burnt as well); 
the same corridor recently hit by an ice storm will seem very 
dark. Fresh blood and body wastes will retain high temperatures 
for a short time. You get the idea. Dwarf-kin and goblin-kin love 
battling the ignorant armies of surface dwellers who enter their 
realms, but hate battling each other, since they already know all 
the best tricks.
    Certain "clean-up crew" monsters, like gelatinous cubes, take 
on special significance for infravision-users. A 'cube is assumed 
here to radiate no heat, and it likely blocks heat transmission as 
well. It might become "visible" to a dwarf or goblin because it 
cuts off the normally expected scenery down a corridor, as if the 
corridor ended abruptly in a cold wall. Humans wouldn't figure it 
out, but a clever dark-dweller would stop, probe, then go another 
direction.
    Newly discarded items like clothing, armor, and weapons would 
reveal much to infravision, like how long they had been abandoned 
(depending on how cool the items were) and whether the items had 
been used--any warm blood on the blade? A newly set underground 
trap, placed by a human who was unaware of his own heat effects, 
would be avoided with laughable ease by a hobgoblin or gnome.
    A few new magical spells suggest themselves for dark-dwellers 
and wizards. If there can be light and continual light, why 
not infrared light and continual infrared light, at the same 
levels of ability and with the same restrictions? A pebble with 
continual infrared light would make a dandy lantern that no 
human could see, though it would immediately give away itself and 
its user to any other infravision-using being within range.
    A "light bomb" can be created by enchanting a pebble with 
continual light, then coating it with mud. Once dried, the 
pebble can be carried in a pouch, emitting no heat at all, until a 
group of infravision-using foes is met. The pebble can then be 
thrown against a wall as the "bomb"-carrier retreats; the burst of 
light will temporarily blind the foes and allow for escape. 
Optionally, an adventurer with the blind-fighting proficiency 
could close his eyes, throw the pebble (probably by the bunch), 
then attack, unaffected by the burst of light.
    A pebble enchanted with continual infrared light could be 
used as a signalling device invisible to normal sight. Placed 
inside a lantern with a shutter, the pebble's radiance can be 
blocked or revealed by opening and closing the shutter. Given a 
form of Morse code, underground creatures could signal to each 
other, silently and unseen, if surface dwellers approach them.
    (A scary thought: In total darkness, a drow can communicate in 
Morse code with another drow 240 feet away merely by blinking her 
eyes. Think about it!)
    A pouch full of cold dust would be useful for detecting 
approaching foes. When scattered on the ground, the perpetually 
low-temperature cold dust would quickly reveal the exact 
location of any being walking over it, even if the being were 
cold-blooded. (The cold dust would be much colder than the 
surrounding environment, providing great contrast.)
    Finally, a game rules variant: sighting ranges for different 
sizes of target creatures. This will complicate the game a bit, 
but I've tried to keep the basics simple.
    First, find the infravision range of the spotter (30 feet, 60 
feet, etc.). Next, find the size category of the target (Tiny, 
Small, Man-sized, Large, etc.). Multiple the infravision range by 
the sighting range modifier, and that's how far the target must be 
before it is normally seen. It's thus harder to spot a rat with 
infravision than it is to spot an ogre, and you can see the ogre 
coming from farther away.

Target's size   Spotter's sighting
category        range modifier
Tiny            1/3
Small           normal
Man-sized       normal
Large           normal
Huge            4
Gargantuan      10

    Using this table, a dwarf can see a hill giant (Huge) coming 
from 240 feet away, since the giant is so big and puts out so much 
heat. A goblin won't be able to see a rat (Tiny), however, until 
the rat is 20 feet away.

Last thoughts

    Infravision is not the only special sense that real-world and 
fantasy creatures have. Minotaurs and hell hounds have superb 
senses of smell (as do normal canines), bats use ultrasonic sonar, 
certain fish sense pressure changes in the water, and electric 
eels sense nearby electric fields, such as those from other fish. 
A little research and some imagination could bring these other 
peculiar senses to life just as this article has hopefully done 
for infravision. It's a strange world, and fantasy makes it all 
the stranger (and more fun).