Night vision devices gather existing ambient light (starlight, moonlight or infra-red light) through the front lens. This light, which is made up of photons goes into a photocathode tube that changes the photons to electrons. The electrons are then amplified to a much greater number through an electrical and chemical process. The electrons are then hurled against a phosphorus screen that changes the amplified electrons back into visible light that you see through the eyepiece. The image will now be a clear green-hued amplified re-creation of the scene you were observing.
Night Vision is deliberately green in color as shading levels in green are the easiest for the human eye to distinguish. Night Vision used to also be available in red, but scientists later determined that green was easier to see and use.
Yes, Generation 1 can be useful in most nighttime situations. Newer Generation 1 devices do offer increased performance from there older predecessors. Generation 1 units typically use an S-20 photocathode and electrostatic inversion to achieve gain. They can offer substantial resolution toward the center of the image tube, while the edges may be blurred. Generation 1 devices are usually inexpensive and can be a good start for the night vision enthusiast.
It varies anywhere from 20 to 800 m. The viewing distance depends on the area, conditions and a size of your target. Overcast conditions, fog, rain and snow will significantly reduce the effective viewing range. On the other hand your viewing range will increase dramatically under clear skies and/or full moon. Light reflective surfaces such as snow or sand will also increase the effective viewing range of your night vision device. Infrared illuminator (IR) may help, especially in enclosed environments.
Though it is true that night vision devices require little light, it is possible to use them in complete darkness with help of an IR Illuminator. Since most of the time you encounter complete darkness in enclosed environments, high magnification power is not a necessity, you'd rather be able to see at a very close range. In this case the most effective viewing device are goggles. Most goggles have magnification power of 1, built-in IR Illuminator, close focus and a viewing range of a few hundred feet.
Night vision can be used for many different tasks such as wildlife observation, amazing what animals will do when they think you can't see them. Other common uses are camping, hunting, home security, night fishing, night boating, night birding, night photography, caving or spelunking, and many other interesting things. One of the most awe inspiring and overlooked uses of higher performance devices is night sky viewing/astronomy. Look up on a clear night with a good Gen 2 piece of equipment and you will just about fall over at what you'll see... Stars, ten times more stars than you've ever seen before, also airplanes, satellites, and other "night sky objects".
Scopes are generally your least expensive option because they contain only one night vision tube. No matter which Gen scope you choose, all will provide you with excellent night vision at a great price.
Binoculars, because they contain two image tubes, cost more than a scope. They tend to be easier to use however, especially if you're new to night vision. While pretty well everyone knows how to use binoculars, scopes take a bit of learning to get used to looking with one eye only. Binoculars also deliver true depth perception while scopes do not.
Goggles are usually the most expensive as they are designed to wear on your head, freeing your hands to do other things. In addition to wearing them, many goggle systems are designed to let you remove the optics unit from the headset and use them just like binoculars, often with optional high power lenses.
If goggles appeal to you but the price is too high, consider a Mono-Goggle system. Just like a scope the price goes down because only one night vision tube is required, but in this case you can wear it while walking around.
When you first get your night vision unit, get familiar with the focus adjustment of the front objective lens and the eyepiece ocular(s). On new units they may be stiff, but they will loosen with use.
On most units the lens cap has a tiny hole drilled into it that will permit a minuscule amount of light to enter, permitting you to test it under daytime conditions. Remember though, never remove the lens cap and operate the unit during the daytime.
Focusing a night vision unit is a two-stage operation. First, aim at an object and focus the front objective lens as best you can. Now focus the eyepiece ocular(s). This second stage is important as it sets up the unit to permit your eye to focus on the green, glowing image that your unit's image tube is generating.
Night vision hand scopes, binoculars and goggles are all legal to use. The use of night vision weapons sights may be restricted in some jurisdictions, so it's best to check with your local authorities on this issue.
The export of some US-made night vision equipment from the United States requires an export license.
On the question of safety, the answer is that night vision is absolutely safe to use. Though it makes for a great, low-budget movie effect, you will not go blind if you accidentally point your night vision unit at a bright light.
In real life, all night vision devices are built with automatic brightness control circuitry (ABC) that dims the unit - or shuts it off completely - if you point it at a bright light.
NEVER expose the opened objective lens of an active unit in daylight. During the day objective lens must be covered by caps. There is a tiny hole in the cap to provide enough light for day time operation. The unit may be turned on during daytime but the lenses must be covered by caps. NEVER aim active unit at intense light sources (i.e. lights, headlamps, campfires, the moon, etc.). This may damage the image intensifier.
An IR illuminator is a device that projects out infrared light similar to a flashlight. However, infrared light is virtually invisible to the naked eye but it is very visible to night vision equipment. Many devises come with a built in infrared illuminator and most of which are short range flood light style that are good for close range and indoor night vision use - usually about 30 yards max distance. There are many circumstances when devices need the help of an IR Illuminator such as inside dark buildings and anytime moonlight and starlight isn't getting to the viewing area like in wooded environments and in areas of shadows created by buildings, trees or other obstructions. Medium and long IR Illuminators are quite different from the built in illuminators as these powerful external illuminators can send a spotlight like beam of infrared light out to distances of up to 500 yards. These valuable accessories can increase the effectiveness of an optic significantly. The down side to any infrared illumination is that if you are trying to operate covertly anyone with even a Gen 1 device will be able to spot you like a shining beacon. Keep in mind that all Gen 1 equipment has built in IR illumination that is always on. The reason for this is that you would see very very little with Generation 1 products without the aid of the IR light. Gen 2 has over 1000 times more light amplification then Gen 1 so an always on IR illuminator is not necessary. Equipment with built in illuminators that are Generation 2 or better have on/off switches for their illuminators and with Gen 1 there is no switch as the illuminator is always on. In summary with high quality equipment you won’t always need an infrared illuminator however in many circumstances it can double the capability of your devise and allow you to see things that would be impossible to see without a long range illuminator.