Night vision goggles have gravitated from the military arena into the public marketplace.
The mention of a night-vision goggle conjures up images of covert military operations; however, it does have more practical applications. A night-vision goggle improves normal human vision in conditions of low light or complete darkness. The main difference between night-vision goggles and a night-vision monocular or binoculars is that goggles have a headset that leaves the hands free. Goggles are better for constant viewing, especially when walking around. Night-vision technology has evolved since World War II, and goggle prices range from several hundred dollars for older technology to over $5,000.
Night-vision devices were first used by the military for navigation, surveillance and targeting, and they are still used for those purposes. Police and security professionals frequently use image-enhancement and thermal-imaging devices, especially for surveillance. Emergency personnel also use night-vision goggles for search and rescue operations.
The general public can use night-vision goggles to improve vision during outdoor nighttime activities. They are helpful to campers, hunters and wildlife observers moving through the woods at night. They are also used for nighttime flying and boating.
The following three basic types of night-vision goggles differ on the number and type of lenses that they use:
Most consumer night-vision goggles are light-amplifying devices. They take a small amount of ambient light in the form of photons from moonlight or starlight into an intensifier tube and convert it into electrical energy in the form of electrons. According to HowStuffWorks.com, the electrons pass through a thin disk that may have more than 10 million channels. The electrons hit the channel walls, which causes the release of many more electrons. These new electrons are reflected by a screen that is coated with green phosphors. The phosphor screen glows to create the green image that is so closely associated with night vision. The green phosphor image is then viewed directly through an eyepiece called an ocular lens.
Generation 1 night-vision goggles require ambient light from the moon and stars, but do not require projected infrared light like older technology. Unfortunately, they do not work well when the sky is cloudy or there is no moonlight. There is some image distortion with this type of technology. Generation 1 devices are effective to a range of 75 to 100 yards.
Generation 2 night-vision goggles have a better resolution and performance than Generation 1. The user can see in a moonless night and other low-light situations. Additionally, the images are much less distorted and brighter. Generation 2 devices are effective to a range of approximately 150 yards.
Generation 3 is the latest technology used by the U.S. military and costs considerably more. It handles even lower light conditions and has a better resolution. The life of the tube is longer than Generation 1 or Generation 2 and may not need to be replaced. Generation 3 devices can recognize a human-sized object at a range of 200 yards or more.
Images produced by night-vision devices have some defects. They may contain a faint hexagonal pattern as a result of the manufacturing process. Night-vision devices may also produce some black spots in the image, which should remain fixed in number and size. According to Nightvision.com, this characteristic is caused by light-amplification systems that use an intensifier with a microchannel plate.
Images from night-vision goggles that use light intensification technology have other differences from those provided by normal binoculars or the naked eye. They do not provide normal depth perception and are very sensitive to reflected light. This means that images in fog or heavy rain may be too bright. Dark-colored objects with a reflective surface may appear lighter than light-colored objects with a non-reflective surface.