This question is asked constantly by people new to low-light optics, and the distinction is fundamental.

Night vision (image intensifiers and digital NV) amplifies available visible and near-infrared light. It shows what’s physically present in the environment — vegetation, terrain features, building structures — because it works with reflected light. It requires some light source (ambient or active IR).

Thermal imaging detects heat emitted by objects. Everything with a temperature above absolute zero emits infrared radiation in the long-wave infrared band (8–14 microns). Thermal cameras detect this emitted heat without requiring any light at all — they work in absolute total darkness, through smoke, and in some cases through light fog or foliage.

Key practical differences:

For hunting warm-blooded game in dense cover, thermal wins on detection performance. For navigation, reconnaissance, and situations where you need to see the environment itself, night vision provides more contextual information.