Dear deer
Out here in Wisconsin, deer are a drag for drivers. The 1.5 million deer in the state cause an estimated 40,000 to 50,000 collisions each year. Evolution apparently neglected to train deer about highways; the animals seem to spring from nowhere, getting injured or killed while damaging cars and occasionally killing drivers.

It's great for the body shops, but murder on deer -- and the 'ol peace of mind. Some people favor reducing collisions caused by record deer numbers with more hunting. But Cadillac offers a solution that's a bit more kind and gentle -- night vision scopes on cars. For slightly south of $2,000, you can get a civilian version of the night scopes that have put modern armies on a 24/7 schedule.

Cadillac introduced the device during its 2000 model year as a way to "see" warm objects beyond the headlight beams. The Why Files wanted to know how well it works. Would it distract drivers from the task at hand -- driving down the road without slamming into phone poles and SUVs? Would it actually call attention to deer, or merely be a nuisance?

We asked for a test drive, but Cadillac insisted we pilot a brand-new Deville for a week's cruise. We imagined visiting Las Vegas to yank the crank on a slot machine, but had to settle for visits to Chicago and an old-time Wisconsin ice cream parlor.

Infrared explained
But what was infrared? Reference books told us it is a form of radiation with a wavelength just longer than visible light, in a range from one micron (one-millionth of a meter) to 1,000 microns.

Infrared is emitted by molecular vibrations in anything that's warmer than absolute zero, which means everything since nothing exists at absolute zero. Although our eyes can't detect infrared, our skin feels it as heat.

Infrared was discovered in 1800 by William Herschel, a German astronomer working in England who broke light waves into various colors with a prism. Herschel noticed that a region with no visible light nonetheless could warm a thermometer. Since the region was past the red light, he dubbed it "infra-red, for "below red." In the years since, infrared has been used to detect heat in various ways, many of them military. Here's more infrared history.

Preamble over?
Yes. Cadillac's night scope is passive system. Here's how it reads infrared radiation from the environment:

Incoming infrared radiation is focused by a lens on an array of detectors.

Each detector pixel is about 50 microns square. Made of barium-strontium-titanate, the detector changes an electrical quantity called capacitance when temperature changes.

This change in capacitance alters the current flow in the detector, so the current in each pixel reflects the amount of infrared it's receiving.

A signal processor converts the signal into digital form, where it is processed and converted back to analog (wave form) data.

A display projects the image onto the windshield, below the normal field of vision. Because the image appears to be at the front of the car, the driver's eyes needn't change focus. Hotter images -- deer, people, the tires on heavy trucks -- appear white, making them more prominent.

Two thousand clams is el-cheapo compared to the infrared detectors on satellites...