Vision scopes, binoculars and goggles are electro-optical
devices that intensify (or amplify) existing light instead
of relying on a light source of their own. The devices are
sensitive to a broad spectrum of light, from visible through
infrared. An accessory illuminator can increase the light
available at the infrared end of the spectrum by casting a
beam of light that is not visible to the human eye.
You do not look "through" a Night Vision product, you look
at the the amplified electronic image on a phosphor screen.
Light enters the Night Vision product through an objective
lens and strikes a photo cathode that has a high energy charge
from the power supply. The energy charge accelerates across
a vacuum inside the intensifier and strikes a phosphor screen
(like a TV screen) where the image is focused. The eyepiece
magnifies the image.
A Night Vision phosphor screen is purposefully colored green
because the human eye can differentiate more shades of green
than other phosphor colors.
Like cameras, Night Vision products have various image magnifications.
The distance at which a human-sized figure can be clearly
recognized under normal conditions (moon and star light, with
no haze or fog) depends on both the magnifying power of the
objective lens and the strength of the image intensifier.
The maximum viewing range of the Moonlight product family
is from 100 feet to 400 feet.