Wow. I'm impressed. I just learned that you can check your remote controls IR output using a digital camera.
You just point your remote control at the digital camera such as a standard webcam or a standard cell phone camera and push the button. It shows up on mine as a white light like an led light when looking at the image on my viewer screen, yet when I point the remote at my eyeball, I see nothing.
Go to RemoteCentral.com, a website that reviews remote controls. They have photos of the IR beam for a number of brands. Some have a very narrow weak beam, others spread a strong wide beam.
Other than maybe needing to windex the fingerprints and cigarette smoke off the little eye on the front, the failure rate of the TV end of the remote system is close to zero. And if the remote just went flying, the odds of the TV end failing at that exact same time are too low to even consider.
... Differing sensitivity ranges -- the camera CCD can "see" the IR and images it onto the display into the visible spectrum. The "raw" IR isn't in the portion of the spectrum visible directly.
The camera, whether film or electronic will see the light in an image differently than the human eye. Even different films and different electronic imaging chips will see the light spectrum differently which is a result of the different material that goes into making them. An electronic camera can "see" the IR energy and records or displays the IR image on the monitor or preview screen, where this IR part of the spectrum is beyond human vision. Sometimes the eye can see things that film or electronic chips cannot see. An example is older black and white film that could not see red, which is why red lights were used in darkrooms, and why Hollywood used brown or dark gray lipstick on women so that lips would not appear very pale in the finished product.
If you wanted an explanation, you should have asked for one. Otherwise, we'll assume the answer is as obvious to you as it is to us.
Why you can't see anything: Those wavelengths of light are called "infrared" because they are longer wavelength (lower energy) than visible red. They are used for remote controls *because* they are not visible to us, yet easily generated and detected by silicon devices.
Why your camera sees it: The camera uses a silicon-based detector, either CCD or CMOS. Silicon is quite sensitive to near-IR, which is one thing that makes near-IR a good choice for remote control communications. So the camera sensor naturally sees the IR, unless the camera incorporates a really effective IR filter to remove those wavelengths before they reach the sensor.
In fact, most digital cameras *do* have an IR filter, because IR is seen as white light by the sensor (it passes through the RGB filters) which reduces saturation and shifts colours. So there is an IR-blocking filter which is effective enough at reducing the effect of IR naturally present in scenes illuminated by the sun or incandescent lamps. But it's not effective enough to *completely* block the very bright IR produced by the LED in the remote control.
BTW, there are video cameras built for security/surveillance that deliberately have high IR sensitivity so the camera plus a few IR LEDs make a "see in complete darkness" camera.
One thing I *have* used this for: determining what a film P&S camera is focusing on. I have a Yashica T4 which has passive IR autofocus, and it's described as "multi beam". If I aim the camera at a piece of white paper that fills the field of view and press the shutter release, a beam of IR light from the camera illuminates several places on the paper - but I can't see the beam myself. A little B&W security video camera aimed at the same paper shows clearly just where the IR beams are hitting the paper.
Looking at the video output on a monitor, I can draw lines on the paper that show the boundaries of where the IR focus beams hit. Then when I look at those marks in the camera viewfinder, I can see where the autofocus spots are relative to the viewfinder markings.
(It should *also* work to simply have the video camera look through the camera viewfinder, and observe the IR directly. But I didn't try that.)
Unfortunately, digital P&S camera mostly use the slower but cheaper contrast-detection autofocus instead of IR autofocus.
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