Night vision and the use of infrared lighting
Having night vision gives you the ability to see in a dark environment. Seeing in the dark is made possible by a combination of two approaches, namely having sufficient spectral range and intensity range.
Spectral Range: Human vision is limited to a small portion of the electromagnetic spectrum called the visible light spectrum. By enhancing the spectral range, a viewer can take advantage of non-visible sources of electromagnetic radiation, such as infrared (IR) or ultraviolet (UV) radiation. For security applications, IR radiation is typically used.
Intensity Range: Sufficient intensity range is simply the ability to see in very small amounts of light. Although the human visual system can detect single photons (under ideal conditions), this is far from adequate for good nighttime viewing.
Through the use of technology (electronics), the process of ‘seeing in the dark’ (night vision) can be loosely grouped into two subsets: passive and active systems.
Passive systems rely solely on the sensitivity of the Vision system to resolve a given screen (or video image). Using only one video camera (CCD sensor) in a dark environment: The viewer will usually be very disappointed. To obtain better light amplification, an image intensifier tube is often used. These devices amplify the available light by a factor of ten thousand times or more. This means that images that are not normally seen at night can be resolved. Unfortunately, these devices require some light to amplify (even if it’s just moonlight or starlight), and are totally useless in zero light conditions (complete darkness).
Active systems use an infrared (IR) illuminator to flood the visible area with light. In these conditions there is so much light that you can use an IR sensitive video camera without having to buy any kind of image intensifier.
Other types of night vision devices (NVDs) include: night vision goggles (or NVGs) and thermal imaging.
NVG uses two eyepieces. They can be configured with an image intensifier tube, where the same image is sent to both eyes, or a separate intensifier tube for each eye.
Thermal imaging cameras are great for night vision use. They exhibit thermal radiation and do not require a light source. They produce an image in the dark that can be seen through fog, rain, and smoke, giving them a huge advantage over other detection methods.