Infravision is the ability to perceive infra-red radiation in a visual sense, so for those with infravision they have sensitivity to the EM frequency spectrum below the band in which \'visible light\' wavelengths exist. There will be graduations of IR frequency, just as graduations of visible light frequency gives us the red ( lowest frequency, borders infra-red ) to violet ( highest frequency, borders ultraviolet ) pattern seen in a rainbow, prism or diffraction grating.. as well as graduations in frequency ( colour analogue to visual light ) there will be graduations in amplitude/intensity ( brightness/darkness analogue to visual light ).
So with infravision it should be very easy to discern differences say between a a natural cavern wall, bricks or tiles, hewn stone, earth, rubble, metal panels and so on. Living and warm blooded creatures will stand out like beacons in such an environment, but the fine detail in \'cold\' structures will still be visible.
Night vision on the other hand is a different beast altogther. It operates purely in the visual spectrum, and gives a higher sensitivity in low-light areas. Owls and other nocturnal hunters with excellent night vision would be hopelessly blind in a dungeon or cave with no light sources, but infravision would function just fine.
I still believe that infravision is superior to night vision. The only disadvantage perhaps would be being \'dazzled\' by intense flares of heat from fireballs or exploding furnaces and the like.. it would be like having a bright torch shone in your face when your eyes have adjusted to the dark.