Imagine if you could only see a single color. I don't mean imagine that everything was black and white, I mean imagine that unless something was a specific color, you couldn't see it at all. Thankfully, most of us are able to enjoy the rich spectrum of vibrant colors that fills the world. The tremendous variety of possible color shades and tints adds immeasurably to our enjoyment of life, and has long provided a creative outlet for artists. Yet my hypothetical question serves to illustrate an interesting fact, one that links scientists and some artistic photographers. All the wonderful colors that we see represent only a very tiny fraction of the electromagnetic spectrum. This spectrum includes microwaves, x-rays, radio waves, gamma waves, and so on. It also includes infrared and ultraviolet radiation. Just as a sound can be described as having a certain frequency, the different colors of light have different frequencies. If a frequency of sound is too high, we can't hear it, even though our dog might. In the same way, if a frequency of light is too high, higher than the color violet, we can't see it. Light of a frequency that is just beyond our ability to see is called ultraviolet light. Just as your dog can hear high frequency sound, some birds and insects can see ultraviolet light. This is why some flowers that may seem plain to us are very appealing to a bumble bee, who sees something completely different.
Frequencies of light that are just below our ability to see, beyond the color red, are called infrared light. Again, although we can't see this color, pit vipers, like rattlesnakes, can. This is very convenient for hunting in the dark, since infrared rays are thermal. Warm bodies, like those of mice, radiate this energy, appearing to the snake like brightly-lit objects in a dark place. Would you like to see what these creatures see?
Through the wonders of technology, this is now possible, sort of. As was mentioned, we can't see this light. Our eyes don't have the ability to detect it. However, photographic equipment has been created that can detect it. It is then converted into colors that we can see. Different frequencies of light, or in the case of far infrared, different temperatures, are represented by different shades. Both still and full motion cameras have been created that can capture these frequencies. Such photography is used in a variety of ways.
Maintenance personnel now routinely use infrared scanners to check for electrical connections that may be overheating, or to see where a building may be losing heat in the winter or gaining it in the summer, based on temperature differences.
Forensic experts are using both still and dynamic ultraviolet photography to document the patterns of injuries, including abrasions, contusions, lacerations, and bite marks. They use both infrared and ultraviolet photography to evaluate forged documents and for a variety of other purposes.
Astronomers use, not just infrared and ultraviolet photography, but sensing equipment covering the entire electromagnetic spectrum.
Perhaps a more interesting use for technology that can convert invisible light to the colors we can see involves artistic photography. Here the photographer has as a goal the creation, or representation, of something beautiful. Infrared and ultraviolet photography are used either by themselves, together, or in combination with more traditional photographic techniques. People, animals, and landscapes take on an almost alien quality when seen with ultraviolet or infrared light.
Color adds richness and variety to the world around us. It's interesting to know that a much wider spectrum of light exists than we can see with the unaided eye. Modern technology has opened this world to us. This is benefiting us scientifically, helping to satisfy our curiosity about the universe, and offering practical applications in a variety of fields. New vistas of artistic expression have also been opened by technology that allows us to photograph the invisible.