Thursday, April 20, 2006

The Heat Is On

Each morning when I go into the kitchen to turn on the teakettle, I pick up a small plastic box and press a bright orange button in the upper left-hand corner. Fifteen feet across the room, a shelf-top stereo system powers up and Vermont Public Radio begins providing me with the day's news and weather. The same technology is familiar to anyone who has purchased a television in the last twenty years—the infrared remote control, a device now widely blamed for robbing us of the eighteen calories per hour we would burn by actually getting up off the couch to change television channels.

Infrared remote controls, first introduced in the early 1980s, were a big improvement over earlier designs, which used wires physically connected to the television's dials, pulses of light, or ultrasonic signals. (The early designs all had serious drawbacks. Wire remotes were slow and sometimes made people trip; photovoltaic remotes don't work well in sunlight; and ultrasonic remotes often make dogs howl.) Today's infrared remote control devices make use of a discovery that occurred 200 years ago, when Sir Frederick Herschel used a prism to split light into its component colors and measured the temperature of each color. He observed that the temperature increased as he progressed through violet, blue, green, yellow, orange, and red, and that the very highest temperatures were just beyond the red section of the spectrum. He concluded that there were invisible rays beyond red that behaved like visible light. Herschel coined the phrase "calorific rays" for the invisible beams; they later became known by their current name, infrared rays.

Despite our inability to see infrared rays directly, Herschel's discovery has proven to be immensely valuable. Infrared cameras pointed out into space allow us to peer through interstellar dust clouds. Other cameras pointed earthward use the infrared portion of the spectrum to monitor the environment, track weather around the globe, and even discover centuries-old footpaths and prehistoric settlements. On Earth, thermal imaging cameras are used in a wide variety of applications, including the maintenance of mechanical systems, the testing of personal computer circuit boards, search and rescue efforts, and medical diagnosis.


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