NIGHT VISION CARS
what is this system
It is a known fact that after dark it is impossible for man to see beyond a few metres in length without the correct illumination and this illumination also has its constraints and during the night times the reflectivity also increases and it is more a judgemental driving rather than a calculative one. The night vision helps the drivers in such cases. It makes a negative image of the image captured by the camera and illuminates the darker part thus enabling the driver to see what lies ahead by looking at the monitor that has been attached in front of the diver on the dash board or some other convenient part of the steering.
how its working
Night vision devices (NVD) work in the near-infrared band at a wavelength of about 1 Micrometer. For comparison, human visual range is about 0.4 to 0.7 micrometers. Unlike thermal imaging systems, which may operate on complete darkness using heat radiation signatures, well beyond the visible light spectrum, NVD's rely on ambient light, often from the moon and stars. The intensifier tubes use the photoelectric effect. As a photon collides with a detector plate, the metal ejects several electrons that are then amplified into a cascade of electrons that light up a phosphor screen. Often a dim star in the sky is enough to illuminate an entire field.
The night vision image does not have color information, and hence monochromatic displays are sufficient. A green phosphor (P22) display is generally used as the human eye is most sensitive to the color green in this wave length, which falls in the middle of the visible light spectrum.
The latest generation of NVD use a green yellow Phosphor (P43), and gives the operator a much more comfortable viewing experience. Current development by Photonis, have also created a gray scale or black & white Phosphor (P45).
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