Night vision is one of the most important factors when considering any kind of video operated spy gadget as this technology allows the viewer to see in complete darkness while the subject is completely unaware. Because infrared light (radiation) falls just below red on the visible light spectrum, making up the wavelengths from about 750 nanometers to about 1500 nanometers, this light cannot be seen by human eyes, but it can easily be seen by many video cameras, making it useful as a covert lighting method in night vision systems.
Read more: Invisible Light Basics DIY tutorial.
