See Infrared with a TV Remote | Try it Yourself!

[waht]

I went into a dark room with a tv remote control. Then I waited a couple of minutes until my eyes adjusted to the dark. Then I pressed a button on the remote and I could see a very faint flickering brownish glow eminating from the IR LED.

I'm assuming this was just a sub-harmonic frequency generated by the non-linear characteristic of a diode, and it just happened to fall in the border of visible light.

Anyway, this was very neat. You guys can try it.

 

[berkeman]

Not a sub-harmonic -- that would be non-physical for the diode. You're seeing the tail in the near-IR. Pretty cool.

 

[Gelsamel Epsilon]

There was a thread in General discussion about how to see IR a while ago.

 

[leright]

After reading the thread about someone's son being able to see infrared light, I mentioned to my optoelectronics professor that some people can actually see a little of the IR spectrum. He looked at me like I was an idiot...lol

 

[berkeman]

After reading the thread about someone's son being able to see infrared light, I mentioned to my optoelectronics professor that some people can actually see a little of the IR spectrum. He looked at me like I was an idiot...lol

Sounds like a good opportunity to put him in your pocket (if you're so inclined). Take a hard copy plus some of your own work to his next office hours.

 

[NateTG]

Playing with IR like that is a bit dangerous because human eyes are not sensitive to it, but it can do lots of damage. Especially when things are otherwise dark (like if you're trying to see IR).

Humans can see in the near UV, but it's usually blocked by the lens which becomes more opaque to UV as you get older. People who have their lens removed because of cateracts can see into the UV, even if they can't focus well. Also, early prosthetic lenses were UV transparent.

 

[EL]

I can clearly see the light from my remote controle. Do different remotes usually differ a lot in frequency? Maybe I just happen to have one which emitts some red light too...have to try another one.

 

[Euclid]

If you can see IR, isn't it then, by definition, visible light?
:)

 

[actionintegral]

Sometimes I watch radio. But it's in black and white.

 

[DaveC426913]

I can clearly see the light from my remote controle. Do different remotes usually differ a lot in frequency? Maybe I just happen to have one which emitts some red light too...have to try another one.

Yes. Some emit red light.

It was https://www.physicsforums.com/showthread.php?t=134077"and I had a control on the test. I could not see the light at all, whereas he could see it quite clearly.

 

[DaveC426913]

If you can see IR, isn't it then, by definition, visible light?
:)

Well, no. I mean, IR is not defined individually by each person. (Does a blind person count the entire spectrum as IR?)
IR is a specific range of freqs, though it is true that it has a "fuzzy border" with visible light.

 

[waht]

Playing with IR like that is a bit dangerous because human eyes are not sensitive to it, but it can do lots of damage. Especially when things are otherwise dark (like if you're trying to see IR).

I specifically chose a remote control because it's a convenient source of low power infrared radiation, it's probably less than 1 mW power output, and IR is not ionizing like UV. Besides, a daily IR dose from sun is much greater, even when pupils are dilated.

I thought about evolution for a little bit. Since every offspring has a little different genes from parents because of random mutations (to increase the chances for survival) it makes sense that a small subset of population would develop a greater sensitivity to infrared and others to UV.

 

[waht]

Yes. Some emit red light.

It was https://www.physicsforums.com/showthread.php?t=134077"and I had a control on the test. I could not see the light at all, whereas he could see it quite clearly.

I can confirm it. Your son was right.

If your remote has a brown filter before the LED, than it would be harder to see then glow.

I tried a couple of different remotes that have the LED sticking out and they all glowed with same intensitiy. The standard wavelength of these diode is about 850 nm.

I'm going to try and get a hold of various IR leds with different wavelength and see which one I can see.

 

[DaveC426913]

If your remote has a brown filter before the LED, than it would be harder to see then glow.

Well yes. But the discrepancy was marked. I looked and looked and looked and looked and saw nothing at all. He made the right call every single time without the slightest hesitation. I clicked and clicked and clicked the button, trying to throw him off, and he might as well have been looking at a flashlight.

I tried a couple of different remotes that have the LED sticking out and they all glowed with same intensitiy. The standard wavelength of these diode is about 850 nm.

Really? Good to know. I had just assumed that they'd all be different. But you're right, they wouldn't be, would they?
Here's http://en.wikipedia.org/wiki/Image:Control-remote-spectrum.png" that shows it peaks just shy of 950nm.

So, what is the average for humans?

Looks like about 700nm. So my kid can see all the way down to 850?
According to http://www.sjsu.edu/faculty/watkins/eye.htm", he's off the charts!

 

[DaxInvader]

Does it change if you wear glasses? Can you see it?

 

[DaveC426913]

Does it change if you wear glasses? Can you see it?

What do glasses have to do with it? It's 6 inches in front of my face!


P.S. Just to prove to myself I wasn't completely insane, I decided to see what my video cam saw. My video cam detects the LED like it's a searchlight!

 

[DaxInvader]

Some glasses has some protection layers.. Anti-reflections.. Or other stuff like it.. Its already hard seeing it with a naked eye.. Just asking the question.

 

[DaveC426913]

OIC.

No. No effect.

 

[DaxInvader]

Thanks then :P