The Electromagnetic Spectrum
Part of understanding your equipment is understanding exactly what it does. Most tools in the investigators arsenal include instruments that record portions of the electromagnetic spectrum. Do you know which wavelengths your equipment records in? Do you know the difference between ultra-violet and infrared light? Did you know your EMF detector, infrared camera, thermal imaging camera, camcorder and your non-contact thermometer are all recording portions of the same electromagnetic spectrum? If you didn’t know the answers to those questions fret not, this article is here to help!
Take a look at this image and the samples of the electromagnetic spectrum from NASA:
“Radio: Your radio captures radio waves emitted by radio stations, bringing your favorite tunes. Radio waves are also emitted by stars and gases in space.
Microwave: Microwave radiation will cook your popcorn in just a few minutes, but is also used by astronomers to learn about the structure of nearby galaxies.
Infrared: Night vision goggles pick up the infrared light emitted by our skin and objects with heat. In space, infrared light helps us map the dust between stars.
Visible: Our eyes detect visible light. Fireflies, light bulbs, and stars all emit visible light.
Ultraviolet: Ultraviolet radiation is emitted by the Sun and are the reason skin tans and burns. “Hot” objects in space emit UV radiation as well.
X-ray: A dentist uses X-rays to image your teeth, and airport security uses them to see through your bag. Hot gases in the Universe also emit X-rays.
Gamma ray: Doctors use gamma-ray imaging to see inside your body. The biggest gamma-ray generator of all is the Universe.“
At the top of the spectrum is low-energy, long-wavelength, low-frequency emissions like radio waves. As you move down the spectrum the emissions have more energy, shorter wavelengths and higher frequencies. Gamma rays are some of the most energetic emissions we can measure. Did you notice the visible light spectrum? This is the portion of the electromagnetic spectrum we can actually see. Compared to the rest of the spectrum we can only see a small fraction.
There are two main concepts you need to understand when it comes to the electromagnetic spectrum. We’ll talk about frequency first. Frequency is just like it sounds, the amount of times something happens in a specified time frame. For example if Jim goes to the grocery store twice per month and Joan goes to the grocery store four times per month, who goes to the grocery store more frequently? Joan does. It works the same for electromagnetic waves.
Electromagnetic (EM) waves are typically measured in hertz (cycles per second). Keep in mind that if we could see these waves they would resemble a wave in the ocean: They grow in size then decrease in a constant cycle. Look at the picture below:
A cycle is complete when the wave finishes this up and down change. It will increase from 0 amplitude to the peak then decrease into the negative range. Once it hits 0 again the cycle of the wave is complete. If we have one complete cycle of the wave every second this would equal 1Hz (hertz). 1,000 cycles of the wave every second would be 1,000hz or 1KHz (kilohertz). This is the frequency of the wave: How many cycles the wave complete every second.
The wavelength is just that, the length of the wave. No we are not talking about the length of time, but the actual physical length. If we could take a ruler and measure it, that would be the wavelength.
Wavelength is directly related to frequency. Higher frequency waves have shorter wavelengths. Lower frequency waves have longer wavelengths. Check out the image below. There is a lot of information so take your time. See the row that says “Radiation Type Wavelength?” The red line shows how the wavelength becomes shorter as we move from low-energy radio waves to high-energy Gamma rays. Now look at the row titled “Approximate Scale of Wavelength.” If we could actually see these wavelengths this is how long they are. Radio waves are as long as a skyscraper! Microwave rays are about the length of a butterfly. Ultraviolet (UV) rays are the length of a molecule. Gamma rays have so much energy they are as short as a single atomic nuclei… Very, very small!
Now wavelength is a very real thing, even though we cannot see it. Get up and take a look at your microwave. You’ll see a metal mesh in the clear window. The mesh is small enough to keep microwaves from escaping, but large enough to allow visible light through. Take a look at the scale. Microwaves have a much larger wavelength than visible light, that’s why that metal mesh can block certain portions of the EM spectrum and not others.
What Measures What?
Now that you have a basic understanding of wavelength let’s talk about what instruments measure certain portions of the electromagnetic spectrum. First take a look at this chart. It breaks down the different portion of the EM spectrum and what frequencies and wavelengths they operate at. I’ll refer to the frequencies different instruments can record.
|300 EHz||1 pm||1.24 MeV|
|30 EHz||10 pm||124 keV|
|3 EHz||100 pm||12.4 keV|
|300 PHz||1 nm||1.24 keV|
|30 PHz||10 nm||124 eV|
|3 PHz||100 nm||12.4 eV|
|Visible||300 THz||1 μm||1.24 eV|
|30 THz||10 μm||124 meV|
|3 THz||100 μm||12.4 meV|
|300 GHz||1 mm||1.24 meV|
|30 GHz||1 cm||124 μeV|
|3 GHz||1 dm||12.4 μeV|
|300 MHz||1 m||1.24 μeV|
|30 MHz||10 m||124 neV|
|3 MHz||100 m||12.4 neV|
|300 kHz||1 km||1.24 neV|
|30 kHz||10 km||124 peV|
|3 kHz||100 km||12.4 peV|
|VF / ULF||Voice
|300 Hz||1 Mm||1.24 peV|
|30 Hz||10 Mm||124 feV|
|3 Hz||100 Mm||12.4 feV|
Generic Camera or Camcorder: A typical camera or camcorder measures in the visible light spectrum 430 – 790 THz. Cameras technically record in the infrared spectrum as well. These waves are blocked out by an infrared filter to block out that light. You can turn a typical camera into an infrared camera by removing this filter. Learn more here. Some camcorders include the ability to record in visible or infrared. Some Sony camcorders have Nightshot which allows you to switch from visible light to infrared recording by the push of a button.
Ultraviolet Camera: Ultraviolet cameras record in the near-ultraviolet spectrum. Some cameras may be capable of doing this by removing the IR/UV filter. However this will turn your camera into a full-spectrum camera which creates other issues. Also keep in mind some cameras are not sensitive to UV light, even with the filter removed. If you have a full-spectrum camera you can use a filter to record only UV light. The glass from an incandescent black-light bulb functions as a poor-man’s visible light blocker, but it will still allow IR light to pass through. Another thing to note is UV light has a smaller wavelength than IR or visible light. That means a UV camera can see through some objects your normal camera can’t. It is not going to give you X-Ray vision, but it will allow you to see through fine mesh.
Infrared Camera: These cameras are essentially the same as a generic camera or camcorder but they have a filter that blocks out visible light. These cameras usually record in the near to mid-infrared range. The exact frequency depends on the filter used and the responsiveness of the CCD.
Full-Spectrum Camera: Full-spectrum cameras record in the near and mid infrared, visible, and near ultraviolet ranges simultaneously. I never understood the point of this because you are is merging more information into one picture, reducing the amount of detail you can see. Different materials and energy responds differently at various wavelengths. Putting these all in one camera is like combining a picture of a dog, a house and a car together. Sure you see all these at once, but it is impossible to see where one ends and the other begins. A much better approach to record in full-spectrum is to use one full-spectrum light source and three cameras. One camera set for infrared, another for visible light and another for UV. This will allow you to compare the same image viewed through different portions of the EM spectrum. That being said I have a cheap full-spectrum myself:)
Thermal Imaging Camera: Works in the 20 – 37 THz range. This range is part of the far-infrared portion of the spectrum. This range is also called thermal infrared or long-wavelength infrared.
Night Vision: Amplifies light in the near-infrared portion of the spectrum around 214 – 400 THz.
Geiger Counter: Most geiger counters will detect EM emissions in the X-Ray and Gamma range. As the frequency of the radiation increases, geiger counters become less accurate in measuring the amount of actual radiation.
RF Detector: These devices can measure radio frequencies between 10 MHz to 8 GHz! Cheaper models have limited frequency ranges and are less sensitive to radio signals. These ONLY detect radio waves and not magnetic and electronic forms of electromagnetic emissions.
EMF Detector: These are similar to RF detectors but typically can detect radio, electric and magnetic forms of EMF. Typically operate at 16 Hz to 3 kHz for magnetic and electric and 50 MHz to 8 GHz for radio waves.
Trifield Meter: A very popular instrument with ghost hunting groups. Like other EMF detectors it will detect AC electric and magnetic fields as well as radio waves. It detects at 40 Hz to 100 KHz for electric and magnetic EMF. For radio waves it will detect anything between 50 MHz to 3 GHz.
AM Radio: Will pick up frequencies between 535 kHz to 1605 kHz.
FM Radio: Will pick up signals between 88.1 MHz to 108.1 MHz.
Shortwave Radio: Can pick up signals from 1.6 MHz to 30 MHz.
And of course there are hundreds of different instruments, radios and devices that can record these waves. These are just some of the more popular examples. Radio waves alone is an enormous area with transmissions across so many different frequencies very close together. This leaves a lot of potential for false-positives. I’ll talk more about false positives and the EM spectrum in a later article.