Cool Cosmos

Seeing Our World in a Different Light - Introduction

We learn much about the world around us by using our eyes. Think about all of the information you obtain and process by simply looking at the world around you. Our eyes are sophisticated detectors that have biologically evolved to "see" visible (or optical) light. There are, however, many other types of light - or radiation -- which we cannot see without the aid of technology. The human eye is sensitive to a small sliver of the full range of radiation we call the electromagnetic spectrum. To fully appreciate the beauty and complexity of the world around us, we need to rely on man-made devices to provide views of the "invisible" world. Medical doctors using x-rays to perform diagnoses and air-traffic controllers using radar to safely guide airplanes are only two examples of how the study of invisible "light" contribute to our well being.

Infrared (IR) light is primarily thermal radiation, a measure of temperature. To the left is a thermal IR image of a person holding a burning match. In this false color image, the white regions are the hottest, the red depicts warm areas, and the coldest portions appear as blue. Note the contrast between the very hot flame and the relatively cool eyeglasses, which do not emit significant amounts of IR radiation. The image to the right is an infrared view of a cat. In this image, the yellow regions are the warmest and the purple areas are cool. Here you can see that the warmest parts of the cat's head are the ears and the eyes, while the coldest region is the kitty's nose. If you have a cat at home, gently feel his/her ear lobes and note the contrast with the cat's nose!

These images give an idea of how different the world around us would appear if we had infrared eyes, and begin to reveal the additional information we could not obtain by simply relying on our eyes. Any object with a temperature above absolute zero (-459.67 degrees Fahrenheit, or -273.15 degrees Celsius, or 0 degrees Kelvin), radiates in the infrared. Even objects that we think of as being very cold, such as an ice cube, emit infrared light!

Visible (left) and Infrared (right) view of Seattle.

Most of what we see with our eyes is the result of indirect (or reflected) radiation, provided by the Sun or by artificial lights. The person sitting across your dinner table is visible because of reflected light provided by another radiation source (typically, artificial lighting). However, if your eyes were capable of seeing infrared radiation, that person would be visible to you even in a completely dark room. Why? Because your dinner companion is presumably alive (!), and hence warm, thereby producing infrared radiation. In general, the warmer that an object becomes, the greater the IR radiation it produces.

The development, testing, and improvement of infrared detectors has resulted from a productive collaboration between aerospace and industrial firms (primarily funded by the military) and university researchers (funded primarily through NASA). These research efforts into infrared detector technologies have led to many useful applications, apart from defense and space science purposes.

We use infrared technology everyday whenever we "click" the television on, or switch channels using a TV remote control. In computers, infrared light is used to read CD-ROM disks. Cashiers use infrared scanners to read standardized bar codes on products, expediting the check-out process. Infrared technology is also used in car locking systems, home security systems, environmental control systems and hand-held temperature monitors. When used as a diagnostic probe -- such as measuring ocean temperature from orbiting satellites, measuring the heat from a person lost in the nighttime wilderness, or detecting structural weaknesses in electrical and mechanical systems -- infrared light permits us to make measurements remotely and to draw factual conclusions without having to touch the objects being measured.

In this web module, we explore some of the common and clever uses of infrared light - in science and art, in industry, and for medical and safety diagnostic studies.