Some cars are fitted with night vision abilities, how do they work

A.� By using an image enhancement system, which picks up objects lit up by infrared beam emitted by the car, for example via special infra red headlights. An image of what lies ahead, obscured to human eyes by the dark, is relayed to the driver, usually on a screen.

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Q.� What is an image enhancement system

A.� They're more commonly known as night vision devices or NVDs.

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Q.� How do NVDs work

A.� Night Vision Devices work using something called an image intensifier or photo multiplier. The image intensifier takes the low level of ambient light of an object and amplifies it to create a brighter version of the image, a little like increasing the brightness on a television.

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Basically, photons of light enter the tube of the image intensifier through a lens and hit the photo cathode. The energy of the photons is sufficient to knock electrons from the cathode. These electrons are accelerated down the tube towards a screen by an electric field of several thousand volts. As the electrons accelerate they gain energy and so when they hit the luminescent phosphor screen the photons are converted back into light to recreate an amplified version of the image seen through the lens.

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Q.� Can I buy a NVDs

A.� Yes, but not a very sophisticated one. You’d probably end up with a first generation model, which have problems with distorted images and a short working life for the tube.

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Second generation of night vision devices are still very expensive and not readily available to the consumer market. These use a series of stages between the photo cathode and the phosphor screen called microchannel plates (MCP). These are thin plates of conductive glass containing millions of small holes. As the original accelerated electrons pass through the holes they cause thousands of further electrons to be emitted from the plate. These microchannels lead to a much stronger and less distorted image than first generation devices.

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A third generation of device that offers even better resolution and image intensity at the present time remains largely in the hands of the military.

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by Lisa Cardy