Infrared, Visible Light, and Ultraviolet Rays: The Electromagnetic Spectrum Radiations

By Robert Hazen, Ph.D., George Mason University

All electromagnetic spectrum radiations, such as radio waves, microwaves, infrared, ultraviolet, x-rays, and gamma rays, travel at the speed of light. They’re all produced by oscillating magnetic or electric fields. And, all these different wavelengths interact with matter by transmission, absorption, and scattering. The electromagnetic spectrum is a continuum with wavelengths varying from many miles to a fraction of an inch.

Infrared Technology: Uses

Infrared technology, from electromagnetic spectrum radiation, is imaging technologies that have been developed by humans. It is very important in a whole variety of ways. For example, there are infrared vision goggles, which can be used at nighttime to detect other people, other warm objects. These were first developed by the military, but they’re finding many other uses as well. 

An infrared kind of imaging system can be used to photograph houses at night and look for warm and cooler areas. One can see how well the insulation is working because the heat will leak out of the house in those places. There are many nonmilitary applications of satellite infrared imaging as well.

For instance, they can be used to track forest fires and monitor pollution by factories. Also, infrared satellites are being used now to monitor volcanoes. When a volcano is about to erupt, the top of the volcano starts getting a little bit warm as the hot magma comes closer to the surface, and one can, therefore, detect whether or not a volcano is about to erupt.

This is a transcript from the video series The Joy of Science. Watch it now, on Wondrium.

Visible Light: Radiation People Can See

Visible light is almost smack in the middle of the electromagnetic spectrum. It covers a very narrow range, only four to seven hundred billionths of a meter. It’s defined as the wavelength that the eyes can detect, and that’s about the range. 

There’s nothing special about this range from the physics point of view, but the eyes’ ability to see this narrow region is what’s so critical, and that’s why it is given a separate category. The visible light spectrum is further divided into colors, and those are smaller divisions of wavelength. The colors of the visual spectrum aren’t equal in width; red and green on the visible spectrum are quite broad, but yellow is extremely narrow. It’s a band from only about 570 to 590 billionths of a meter, very narrow range.

Study of Visible Light by Issac Newton

Isaac Newton made a very interesting demonstration in 1665 and 1666. He studied the nature of colors and realized that all the colors of the rainbow, when combined, create white light. He used prisms to decompose white light into colors, and then a second prism to reassemble those colors back into white light. 

It turns out that the eyes have three different kinds of color receptors called cones. These detect red, green, and blue, and when one combines red, green, and blue together at the same time, they perceive the color as white. Newton realized this and developed something called the Newton Color Wheel. 

Learn more about the electromagnetic spectrum.

Ultraviolet, the Powerful Electromagnetic Spectrum Radiation

Ultraviolet radiation is from about ten to four hundred billionths of a meter in wavelength, getting to higher and higher frequencies, higher and higher energies. The energy of ultraviolet radiation is comparable to the energy that holds atoms together, which is why when ultraviolet radiation strikes, the skin it can disrupt bonds. It can destroy molecules and, therefore, kill cells.

Ultraviolet radiation is itself often divided into three distinct sets of wavelengths. The longest ultraviolet wavelength is called near UV. That’s between 300 and 400 billionths of a meter, and is primarily absorbed by the skin. It causes the chemical change called tanning and also causes the production of vitamin D, which turns out to be pretty important. 

Then there is radiation between 200 and 300 billionths of a meter. That’s called the far ultraviolet, the far UV that penetrates more deeply into skin and can kill cells. And then, finally, there is radiation of even shorter wavelengths. That’s called extreme ultraviolet, and that radiation is absorbed by the air, so it does not come down to the Earth’s surface.

Learn more about relativity.

Sunblocks: The Best Solution against UV Rays

The shortest ultraviolet rays that come through the atmosphere are harmful, and sunblocks can block out these harmful rays. Sunblocks are rated with a number. The number tells if there is a certain exposure without sunblock in one hour.

Sunblocks are really fascinating chemicals. The trick for chemists in developing sunblock was to find a substance that could be applied in an extremely thin transparent layer. And then it had to be a water-insoluble layer because people go swimming. It also had to be transparent to visible light and opaque to ultraviolet light. 

Fluorescence: A Brilliant Use of Ultraviolet Rays

There is one use of ultraviolet called ‘black light’, or fluorescence. The brilliant fluorescent display of DayGlo materials is one example in everyday life. This is when ultraviolet radiation hits an object, and then it glows brightly just in daylight. 

In ordinary daylight, there are two objects that just look dull, sort of pale yellow or gray. But, let’s imagine putting these same objects with the lights turned off using ultraviolet radiation. When ultraviolet light is shone on these materials, the materials absorb the ultraviolet and then re-emit some of that energy as visible light, and that’s the phenomenon of fluorescence. So, here, a previously dull, gray rock, a gray powder becomes a brilliantly fluorescent rock and invisible ink, which can be used to send messages.

Common Questions about Electromagnetic Spectrum Radiations

Keep Reading
The Concept and Forms of Energy and Energy Conversion
Conflicting Thoughts about the First Law of Thermodynamics
The Nature of Science and Its Various Disciplines