Why do remote controls use infrared light instead of other wavelengths?
In: Technology
All those IR remote controls use an LED (light-emitting diode) as the light. As it turns out, the first LEDs created were red LEDs, followed by yellow, green and only much more recently blue. So the original choices were really only red or infra-red. Of the two, infra-red has the advantage that it looks more magical: you press a button, can’t see what’s going on, and shazam! your TV changes channel.
At this point, infra-red has the advantage that it’s cheap and well-understood: you can buy essentially “kits” for your product to make your remote.
TL/DR: infra-red was available and cheap. Other colors, not so much.
I know right? Emitting small amounts of gamma radiation should be harmless.
It’s cheaper and easier. For infrared you need an infrared diode on the transmitter, and an infrared receiver on the TV. Cheap and easily available parts. For a radio, you would need an oscillator, modulator circuit, and antenna on the transmitter, and a antenna and receiver/demodulator circuit on the TV. More parts, which translates to more expense. The cheaper solution works for the required application, so that’s what they go with.
The remote control is actually a pretty bright blinking light. People hate bright blinking lights, especially in very dark rooms. By using infrared, the light can be bright, yet invisible to human perception.
Infrared can also use a black piece of plastic for filter out visible light, while passing the infrared light through it, as if it were clear, so noise can be filtered out.
Some do use other wavelengths. Man, I miss my boxee box remote. It used bluetooth(I think), no worries about pointing it in the right direction, always worked perfectly. And yet my $4500 TV…POS Infrared I have to carefully point in the right direction, doesn’t work if I’m a bit too low…
Because IR transceivers are easy and cheap to make. Longer wavelengths need increasingly long antennae. Shorter wavelengths are visible(which would be really annoying), and as they get shorter, it becomes harder to make components that work with those wavelengths.
We use longer wavelengths(microwaves) for wifi and other communications in the home with about the same range, because microwaves can go through walls. Near IR has the limitation that it can’t go through walls, but usually if you don’t have line-of-sight to the TV, you aren’t watching and don’t need to control it.
The [top answer](https://www.reddit.com/r/explainlikeimfive/comments/brqi1n/eli5_why_do_remote_controls_use_infrared_light/eofqlgi/) already covered this a bit, but I want to expand upon one thing.
Some early remote controls, like the “Flashmatic”, worked by having a photosensitive receiver at each corner of the TV screen. You would control volume or channel, respectively, by shining a light on one of these.
The problem here may be pretty obvious: a stray sunbeam, a reflection off a watch/glass/mirror, or just some asshole with a flashlight can now flip through your channels or max your volume and there’s nothing you can do.
fun fact, if you point your phone camera at the tip of your remote and push a button you will see the light turn on in your phone camera but not with your eyes
Related, some early remote controls used high frequency (15,000-20,000hz+) sound instead of light. The researchers developing the technology were mostly old (enough) men who’s hearing had degraded to the point that they couldn’t hear the remotes. Their young secretaries and lab assistants on the other hand *could* hear the sound of the remotes and *hated* them. The rise of transistors and IR LEDs are what finally killed this version of the technology.
Edit: These [early remotes](https://www.youtube.com/watch?v=PlgSuaIHYsY) are also where the slang “clicker” for remote controls came from due to the fact that some made a distinctly audible click.
IR is cheap and energy-efficient.
Also, the waves attenuate very quickly and can’t penetrate through material, which is actually very beneficial for TVs.
If the waves could over-penetrate, you would have to worry about your neighbor changing your channel. Generally speaking, you’re only going to be using the remote in front of the actual TV, so LOS isn’t an issue.
Not only that, but the lack of interference from other TVs makes it easier to program the remote itself, because you don’t need as many complex ID mechanisms to make sure the right remote is interacting with the right TV.
You can use much more generic signals because of this, which makes everything cheaper and simpler.
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