Using your mobile phone, you can see infrared radiation – a normally invisible part of the electromagnetic spectrum. Ken’s Tech Tips looks at some of the physics of electromagnetic waves and explains how you can see this invisible world – and you don’t need anything more than the mobile phone in your pocket.

What is infrared radiation?

Infrared is a form of electromagnetic radiation. Other forms of electromagnetic  radiation (EM radiation) include visible light, x-rays, microwaves (the EM waves that wi-fi networks use and also the waves that cook your food in microwave ovens) and radio waves. The difference between all these different forms of radiation are the wavelength of the EM wave. We can illustrate this electromagnetic spectrum (CC-licensed image from Wikipedia):

What is the difference between visible light and infrared?

Visible light and infrared are both forms of electromagnetic radiation but with different wavelengths. Visible light has a wavelength of between 400nm and 700nm (a nanometer is so small that we can fit 1,000,000,000 in just 1 meter). We can only “see” the EM radiation in this range. At 700nm and longer, we enter the realm of infrared radiation.

Why can mobile phone cameras “see” infrared?

Most cameras are designed to capture an image of what people can see. Hence a good camera would only detect EM radiation in the visible light spectrum (between 400nm and 700nm).

Yet the charged couple devices used within cameras are typically manufactured to pick up EM radiation between 300nm and 1100nm. This means they are capable of detecting infrared light too (between 700nm and 1100nm is infrared).

To improve image quality, camera manufacturers typically add films and filters to block out infrared light and ensure only visible light reaches the CCD. If the infrared radiation was recorded by the camera and appeared in our photos, the photos would not be an accurate representation of what we can see – i.e. what we want to photograph!

Mobile phone cameras tend to be produced a lot cheaper than proper digital cameras and hence the vast majority of mobile phone cameras have a much thinner film/filter to block out infrared light. The lack of infrared filter is one reason photographs taken on mobile phones don’t look as good as those taken on proper digital cameras but it also provides us with an opportunity to use our mobiles to “see” in infrared.

How can I harness this fact?

Simply point your mobile phone camera towards a infrared light source and you can begin to see this new invisible infrared world!

For example, stick your phone camera in front of a television remote control and start pressing some buttons: you’ll see a few flashes of light (your remote uses invisible IR radiation to communicate with your TV – you wouldn’t normally be able to see this radiation as our eyes are not sensitive to the infrared wavelengths used by the remote). If you’ve got a Nintendo Wii, point your phone camera at the sensor bar. You’ll notice the sensor bar emits invisible IR radiation (this is how the Wiimotes track your movement).

Unfortunately, you won’t see the world in true infrared. Your mobile phone camera is sensitive to visible light too – and fortunately (although unfortunately in our case) this always registers much brighter on the CCD and drowns out the infrared image. If you’re really serious about seeing the world in infrared, you can pick up an infrared filter from Amazon. These filters will block out visible light and hence allow you to get a better image of the invisible infrared world.

Your Comments 20 so far

We'd love to hear your thoughts and any questions you may have. So far, we've received 20 comments from readers. You can add your own comment here.

  • Dmitri Toptygin said:

    “(a nanometer is so small that we can fit 100,000,000 in just 1 meter)” – you have to add one more zero to this number. It must be 1,000,000,000. Also silicon detectors can detect wavelengths from 200nm to 1100nm, not from 350nm to 1000nm. For example, Neodymium YAG lasers produce 1064nm wavelength, and common Silicon CCD cameras can see it just fine.

    • Hi Dmitri,
      Thanks so much for this and for your input. It’s so lovely to see that the article is still being read so closely eight years after I wrote it! I’ve amended the typo regarding the length of a nanometers. Regarding the spectral range of 200nm-1100nm, is this a fairly standard figure across all silicon camera sensors (e.g. based on band gaps) or does it vary on a camera-by-camera basis? The numbers I wrote in this article were probably a super-rough approximation eight years ago, so definitely happy to amend if it isn’t accurate.
      Thanks so much,
      Ken

      • Dmitri Toptygin replied:

        Hi Ken,
        I found your article using Google search engine. Yesterday I tried to use my cell phone (Motorola Moto G4 XT1621) to take a photo of a laser beam of 844 nm wavelength. This was a Ti-sapphire laser. I found that my cell phone was completely insensitive to 844 nm wavelength. The beam was so powerful (800mW) that I felt burning heat when I briefly put my hand in its path. When I used an infrared viewer, I could clearly observe the spot on a white screen. I had to document the shape of this spot and to email it to a company in Europe, so I tried to use my cell phone. The phone did not see the spot at all. Then I started to search information on the internet, and your article came first in google search. Now regarding the spectral range: all silicon sensors have the same long wavelength limit of sensitivity (1100 nm), which is equal to the band gap of silicon semiconductor converted wavelength units. Other sensors (like Germanium or Indium-Gallium-Arsenide) sense much longer wavelengths because they have smaller band gaps. The short wavelength limit for silicon photodetectors depends on the material of the window that protects the semiconductor from the humidity in the air (without the window the device will live less than a month). If the window is made of quartz, then the range is from 190 nm to 1100 nm. If the window is made of glass, then the range is from 330 nm to 1100 nm. Here is some information about the spectral ranges of different photodetectors: https://en.wikipedia.org/wiki/Photodiode And here is the most typical sensitivity curve for silicon photodetectors: https://en.wikipedia.org/wiki/File:Response_silicon_photodiode.svg

        • Hi Dmitri,
          This is fantastic information! Thank you so much again for sharing with me – I’ve amended the article above and I’m sure the further information you’ve posted will also be super helpful to other readers of this page.
          Obviously, I would strongly advise other readers *not* to play around with powerful lasers however, as that could cause potential injury or harm to themselves & their devices.
          Thanks again!
          Ken

  • Fabian Lee said:

    I have a Samsumg S5 and want to see the infrared spectrum around me. Is there any place I can purchase something that could connect to my phone or I could use with me S5 to see the infrared spectrum.
    Thank You,
    Sincerely, Fabian Lee

  • Eberhardt Kalmar Huhn said:

    If I use a device such as this, will I be able to use my smart phone camera monitor to see whatever the infrared light illuminates in an environment that is pitch black to the unaided human eye?

    • Hi there,
      This looks like it’s essentially an infrared torch? If you have a smartphone camera that’s able to pick up infrared light, it’s possible this could help you. However, it’s worth double checking how sensitive your phone really is to infrared light (newer smartphones may be less sensitive than early cameraphones from back in 2010) – and I’ve never used an infrared illuminator so not really able to comment very much on this!
      Ken

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