Thursday, November 8, 2012

Night Vision

Night Vision Night vision is a catch-all phrase that refers to any of the methods available to see in low light conditions. The technologically based methods are thermal imaging and image enhancement, with different categories in each of these methods. Biological night vision is something only possessed by animals, usually nocturnal predators or creatures that primarily live in low light conditions.

Biological Night Vision
Many animals possess an extra bit of tissue in their eyes that humans do not have. This tissue reflects the available light back into the retina increasing the amount of light to see with. Some other traits such as larger pupils and unique adaptations in the visual properties of the eyes also enhance the low light vision of these animals.

Night Vision Devices
Some night vision devices work on a similar principle as biological night vision by capturing the available light and then amplifying it. This happens by capturing the ambient light and near infrared light and converting it to electrons. These electrons push through a microchannel plate that causes collisions to excite the atoms and generate more electrons. Converting this greater number of electrons back to light increases the amount of light used for sight. This is usually known as image enhancement and is how night glasses and low light cameras work.

Infrared Light
Infrared light is best thought of as three different types of light. Two types of this light reflect off of objects, but this is not visible to the human eye. They are known as near infrared because it is closest to the visible spectrum of humans and mid infrared which is further away from the human spectrum range. Objects emit the third type of infrared light and the hotter an object is, the more infrared light it emits.

Thermal Imaging
Thermal imaging makes use of infrared light emissions from objects. This light is not visible to the human eye, but cameras can capture it. Thermal imaging works in near darkness conditions and does not require ambient light to function. Thermal imaging devices work by focusing the infrared light of all the objects in view onto an array of infrared detectors. These detectors convert the information into a temperature pattern known as a thermogram. This is translated into electrical impulses and sent to a processing unit. This converts the impulses into data for displaying on a screen. The performance of thermal imaging devices improves if the infrared-detector elements are kept at a low temperature, but this is impractical for field work or transportable devices.

Active Infrared Imaging
This type of night vision combines the capture of near infrared light with cameras that can detect it. This produces a black and white display with much greater resolution than other types of night vision technology. It is most common in security camera applications of a static nature like protecting a warehouse or residential home. It is not viable for tactical military operations because other types of night vision devices can spot the infrared light, and it would give away the position of the troops using it.

Biological Thermal Imaging
It is worth noting that some animals are sensitive to thermal images as well. Snakes like the cobra are known for being able to strike the hottest areas on their prey's body. This makes their poison attack more effective since the hottest parts of the body are usually where the vital organs are located.
Night vision technologies have become popular due to their use in movies and television shows, but their function is generally misunderstood by the public. Night vision devices use available light to work and are not functionable in complete darkness. Thermal imaging devices are more useful in situations of greater darkness since they are not so reliant on light.


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