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Usually we are not able to see infrared rays with our naked eyes. But we could see it when we watch it through a digital camera (or mobile camera). Why it happens?

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  • \$\begingroup\$ Off-topic? Really? I thought the basic principles on which electronic devices work were on topic here? This is clearly related to the technology of CCD sensors used in digital cameras. Where would the OP ask such a question if not here? Physics stack exchange is just barely a place for that question, since it is a technology problem, even if strongly related to the underlying CCD physics. I'd really vote for reopen this. \$\endgroup\$ – Lorenzo Donati -- Codidact.com Jun 5 '15 at 21:20
  • \$\begingroup\$ Yes. To try this at home, grab your TV remote, which uses IR light to send information to your TV and open the front-facing camera on your phone. Next, point the front end of the remote at the camera and press any of the remote buttons. The IR light that is normally not visible will be completely visible on your camera screen. Well I’ll be darned. This works! (iPhone 7) \$\endgroup\$ – joan Jan 17 '19 at 13:02
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This isn't really an electrical engineering question, but the short answer is that your eye has limitations. All light is a subclass of a larger form of energy called electromagnetic radiation.

spectrum

You can't see EM radiation with a wavelength shorter than around 730 nanometers, or what our brains perceive as red. However, your camera doesn't have the same limits, and will pick up the infrared light and try to display it just like any other light.

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  • \$\begingroup\$ Does anyone know why it shows up as white though, when the bandwith of the color sensors show infrared only effecting the red sensor? \$\endgroup\$ – Myforwik Dec 16 '12 at 6:06
  • \$\begingroup\$ Because the RGB sensors in the camera all respond to white light (broad spectrum including infra-red); it is the screen of filters it front of them that filter out R,G or B light. Apparently all of those filters pass infra-red light to about the same extent. \$\endgroup\$ – Brian Drummond Dec 16 '12 at 12:13
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Your camera is based upon Si, which has a bandgap of 1.12 eV which means that for light that is ~ 1.1 u and shorter the camera can possibly detect it. This range of wavelengths is in the part of the spectrum called Near-IR. You eyes cannot see wavelengths LONGER than 720 nm. Near IR transmitters used in TV remotes etc. typically are 850 nm.

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