A long time ago, some races and monsters had the Infravision trait, which allowed them to see in the dark the heat traces of living creatures.

This had very interesting aspects. The drow's sign language\$^1\$ used the heat traces left in the air by the hands to convey messages. In order to become totally invisible in the darkness, one had to magically hide their body heat (see the attack to House DeVir in the novel Homeland).

Nowadays, since the 3rd edition has been published, the Infravision has been changed into the more manageable Darkvision, that allows to see in shades of gray instead of seeing the heat traces when in darkness.

Is there any in-world explanation in the novels, manuals, adventures or in other official sources about how this change occurred in the Forgotten Realms?

\$^1\$ It has been adapted to the 3rd edition Darkvision trait, as explained in the Forgotten Realms Campaign Setting 3rd edition, see here.

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    \$\begingroup\$ Tangentially related: Why do duergar have Sunlight Sensitivity? \$\endgroup\$
    – Kirt
    Sep 21, 2022 at 22:25
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    \$\begingroup\$ When the game was invented, people understood infravision as an analogue to use if IR equipment that the military was just then bringing into common use. By the time of 3.x being publisned, low light vision devices (like NVGs) that were not IR based had become commonplace in advanced militaries (and elsewhere in security applications). There is nothing "in universe" that explains this. WoTC just decided on a tech upgrade. \$\endgroup\$ Nov 30, 2022 at 16:50
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    \$\begingroup\$ Not a lor explanation, but other issues with "infravision" . . . if it's understood to work by detecting heat, that causes all sorts of fiddly issues . . . you shouldn't be able to see a room-temp trap or probably an undead. But "darkvision" now, that's magic, and it just let's you see in the dark, as described in the rules. \$\endgroup\$
    – Jack
    Nov 30, 2022 at 18:11
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    \$\begingroup\$ @Jack As I wrote in the above comment to Korvin, I think they switched because Darvision is simpler to use in game. Moreover, it is not magic. \$\endgroup\$
    – Eddymage
    Nov 30, 2022 at 18:26
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    \$\begingroup\$ Lorewise, recent Drizzt novels still mention seeing body heat. And time in Menzoberranzan is still tracked by heating up Narbondel once a day and being able to see it cool down over the entire day. \$\endgroup\$ Dec 1, 2022 at 18:36

1 Answer 1


Vecna blew up the multiverse.

Simply put, the in-universe explanation of the changes between 2e ADnD and 3e DnD was explained by the adventure Die Vecna Die! by Bruce R. Cordell and Steve Miller.

To quote the adventure itself:

Even with Vecna's removal, his time in the crux effected change in superspace. Though the Lady of Pain attempts to heal the damage, the turmoil spawned by Vecna's time in Sigil cannot be entirely erased. Some Outer Planes drift off and are forever lost, others collide and merge, while at least one Inner Plane runs "aground" on a distant world of the Prime. Moreover, the very nature of the Prime Material Plane itself is altered. Half-worlds like those attached to Tovag Baragu multiply a millionfold, taking on parallel realism in what was before a unified Prime Material Plane. The concept of alternate dimensions rears its metaphorical head, but doesn't yet solidify, and perhaps it never will. New realms, both near and far, are revealed and realms never previously imagined make themselves known. Entities long thought lost emerge once more, while other creatures, both great and small, are inexplicably eradicated. Some common spells begin to work differently. The changes do not occur immediately, but instead are revealed during the subsequent months. However, one thing remains clear: Nothing will ever be the same again.

The change between infravision and darkvision was part of the 2e to 3e rules updates; it would have been covered under this. In particular, it notes that "some common spells begin to work differently", and this would include the 2e spell Infravision and its 3e counterpart Darkvision.

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    \$\begingroup\$ Nothing in that (admittedly awesome) quote mentions infravision, darkvision, or abilities like them. It's definitely possible that a cataclysmic multiverse-shaking event changes how certain creatures' eyes work, but do you have any evidence that supports it? \$\endgroup\$
    – GMJoe
    Dec 1, 2022 at 20:57
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    \$\begingroup\$ @GMJoe It's just a longer version of "a wizard did it" 😊 \$\endgroup\$ Dec 1, 2022 at 21:17
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    \$\begingroup\$ Although this answer reports interesting information about the switch from 2ed to 3rd ed, I am not asking about the spell but about the racial trait. \$\endgroup\$
    – Eddymage
    Dec 1, 2022 at 22:11
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    \$\begingroup\$ @Eddymage: Sure, but this the only edition switch lore you're likely to find. The whole damn multiverse changed, drastically. All changes from 2E to 3E were caused by Vecna trying to control everything and failing. How that caused the changes, nobody can fully explain, but it's the only in-world lore explaining it. For all we know, fixing the damage effectively meant shunting the entire multiverse into a different origin track where infravision had been darkvision from the beginning. They never detailed in-universe reasons for the change beyond this. \$\endgroup\$ Dec 2, 2022 at 1:34
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    \$\begingroup\$ @KorvinStarmast That's hilarious - but there's still no mention of the racial ability anywhere here, making the "a wizard did it" explanation pure speculation with no evidence to back it up. \$\endgroup\$
    – GMJoe
    Dec 2, 2022 at 12:16

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