In our previous night vision discussion, we covered the basics of night vision technology with a focus on the three generations of Image Intensification (I²) night vision devices (NVD). This is the most common type of NVD and is generally the first type that law enforcement agencies look at when planning to purchase NVDs.
But just as there are degrees of I² night vision generations, there are some detailed evaluation criteria that should be kept in mind in addition to those already mentioned. The potential NVD should be dual use, capable of being used both as a handheld observation device and a weapon-mounted sight. Purchase from a manufacturer with a track record of manufacturing and delivering dual purpose clip-on NVD. Choose a manufacturer that can provide references to reputable users (DOJ, DOD, DOE, etc.). Beware of knock-offs. Many unscrupulous manufacturers make their units look like the originals and their trade names sound like the real devices, when they are not. Don’t select a device whose objective lens and output lens are at different heights. This will result in a parallax error that must be mentally compensated for by the user. Select a device whose output lens size is larger than, or as close as possible to the size of, the input lens of the day sight. Smaller lenses will reduce brightness at higher day sight magnifications.