Thermal imaging cameras are not exactly cameras. Rather, they are sensors that can detect the presence of heat (or infrared or thermal energy). These devices are useful for detecting radiation. All objects emit some infrared rays. The more infrared rays that an object emits, the higher will be its temperature. Thermal imagers can spot minute difference in heat. This enables them to depict this in the form of an image (or thermogram) on a screen. Some devices use a range of colours for representing temperatures. Thermal cameras do not require light for producing images. This is because they focus on detecting radiation. In contrast, image intensification night vision devices require at least a small amount of light for functioning.
In many cases, night vision cameras will be ideal for use at night. This is especially so when the moon and the stars are bright enough for the device to yield a good image. However, you will probably not be able to use night vision devices in places that feature no ambient light. To cope with this dependency, many night vision devices feature infrared illuminators. These illuminators work in a manner similar to flashlights. Unfortunately, they will reveal your position too. On a hunting expedition, this might not be an issue. But, because of this shortcoming, people seldom use these illuminators in their night vision devices during tactical and stealth operations.