How Night Vision Works – Part 2

Low-Light Imaging - 
Today, the most popular and well recognised method of conducting night vision covert surveillance is based on the use of Image Intensified Night Vision Devices (NVD's) & Night Vision Goggles (NVG's). Image intensifiers are commonly used in night vision goggles and night scopes. More recently, on-chip gain multiplication CCD cameras have become popularized for performing low-light security, surveillance and astronomical observation.

Image Intensifiers -
This method of night vision amplifies the available ambient light to maximise better vision. An objective lens focuses the available ambient light (photons) onto the photocathode of the image intensifier. The light energy causes electrons to be released from the cathode which are then accelerated by an electric field to increase their energy level (speed). These electrons enter holes in the microchannel plate & 'bounce off' the internal specially-coated walls, generating more electrons as the electrons bounce through. This creates a denser 'cloud' of electrons representing an intensified version of the original image.

HOW THEY WORK: This method of night vision amplifies the available light to maximise the best low-light vision. An objective lens focuses available light (photons) on the photocathode of an image intensifier tube (IIT). The light energy creates electrons released from the cathode which are subsequently accelerated by an electric field to increase their speed (energy level). These electrons enter holes in the microchannel plate & bounce off the internal specially-coated walls which generate more electrons as the electrons bounce through. This creates a denser "cloud" of electrons representing an intensified version of the original image.

The final stage of the image intensifier involves electrons striking a phosphor screen. The energy of the electrons results in 'phosphor glow'. The visual light shows the desired view to the user or to an attached photographic camera or video device. A green phosphor is used in these applications because the human eye can differentiate more shades of green than any other color, allowing for greater differentiation of objects in the picture.

All image intensifiers operate in the above fashion.

Technological differences over the past 40 years have resulted in substantial improvements to the performance of these devices. The different criterion's of technology have been commonly identified by distinct generations of image intensifiers. Intensified camera systems usually incorporate an image intensifier to create a brighter image of the low-light scene which is then viewed by a traditional camera.

Part 3 coming soon...