Here are the entirety of the infravision rules as they existed in 1981, per page B21.
PET PEEVE: I have never seen a computer game that attempted to simulate infravision. If you have, please leave a comment!
Here's some random dungeon art I googled up. A background from the computer game Darkest Dungeon, maybe? This is what your normal torch- or lantern-bearing crew would see.
With infravision, color is determined solely by temperature. And things left laying about a dungeon for centuries will tend to be at the same temperature. Without a proper light source, the party elf or dwarf might see something like this:
It's a subtle difference, but that weird rock formation on the left no longer pops out, and those wine (potion?) bottles will be a little harder to find. Now let's add some monsters to the scene, first by normal vision:
The red dragon, skeleton, and troll are all pretty easy to see. Not quite the same scenario using infravision:
The internal heat of the dragon makes him almost too bright to look at. The troll is basically unaffected. The skeleton has become the same grey as the walls and floor. Undead are hard to spot via infravision because of their tendency to be the same temperature as the background.
Note that my interpretation here is the most generous one I can make, based on the rule above. You could argue that infravision is in fact must worse at picking out details than normal vision, hence the 'no reading' clause. Maybe infravision actually looks more like this:
