Night Vision
- Active Illumination
- Image Intensification
- Thermal Imaging
Active Illumination
Lowest cost. This is basically an infrared camera working with an infrared illuminator. Range is limited to distance of infrared source. Easily detectable. The light source is closer to the visual portion of the spectrum so that it is near visible yet still below human eye perception.
Image Intensification
Vietnam War era "Starlight Scope" and modern Military NVGS fall into this category. Uses only existing light and through magnification the light level is useful to the human eye. These are lighter and more real time. They produce no detectable light source.