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Random theoretical qustion about LED frequency

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bonedoc
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2011/01/05 08:50:15 (permalink)
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Random theoretical qustion about LED frequency

Well, I have been working on a couple things on the side, as I wait for some parts to get here from China. I was thinking about frequencies above and below the visible spectrum.

At radio shack, there are Infra-Red LEDs, which obviously cannot be seen when on because the frequency is below the visible spectrum.

Here is the question:

Lets say I take a blue led and I create a PWM on it that is in the infra-red spectrum. Even though the LED is blue, could I use it, say as a remote control LED? I dont see why. I assume it would still be invisible because of the rate.

Give me your opinion.
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    MBedder
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    Re:Random theoretical qustion about LED frequency 2011/01/05 09:08:55 (permalink)
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    bonedoc
    At radio shack, there are Infra-Red LEDs, which obviously cannot be seen when on because the frequency is below the visible spectrum.

    Here is the question:

    Lets say I take a blue led and I create a PWM on it that is in the infra-red spectrum. Even though the LED is blue, could I use it, say as a remote control LED? I dont see why. I assume it would still be invisible because of the rate.


    You made my day, man!LoLLoLLoLLoLLoLLoLLoL
    post edited by MBedder - 2011/01/05 09:32:45
    #2
    bonedoc
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    Re:Random theoretical qustion about LED frequency 2011/01/05 09:27:41 (permalink)
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    Is my question like the below image?

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    #3
    bonedoc
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    Re:Random theoretical qustion about LED frequency 2011/01/05 09:29:06 (permalink)
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    Or this?

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    MBedder
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    Re:Random theoretical qustion about LED frequency 2011/01/05 09:33:29 (permalink)
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    No, it's much, much betterLoL
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    bonedoc
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    Re:Random theoretical qustion about LED frequency 2011/01/05 10:11:48 (permalink)
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    Seriously, what if you have a blue led that you are flashing at the infrared. Will a a blue frequency or infrared frequency be read? The color blue is at a higher frequency than the infrared. So, it must be both?

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    Ian.M
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    Re:Random theoretical qustion about LED frequency 2011/01/05 10:31:01 (permalink)
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    IMHO it will just melt wink   700nm (right down at the bottom of the red end of the visible spectrum) is 428274.94 GHz !!!!  I dont even want to *THINK* about pulsing anything that fast . . . . LoL

    One more thing:  Lets suppose you still have a nearby AM transmitter.   Take a simple coil of wire of a couple of meters diameter.   If you are in the transmitting station's parking lot, you can easily get enough power from such a coil to light a torch bulb.  Hook it up to a normal speaker and you will hear NOTHING, because although the signal is modulated at an audio frequency it has no actual energy content in the audible frequency range.


    post edited by Ian.M - 2011/01/05 10:54:59
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    bill190
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    Re:Random theoretical qustion about LED frequency 2011/01/05 11:02:55 (permalink)
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    Wouldn't IR need to be about 1,000,000,000,000 Hz?

    The Pic PWM calculator does not seem to like that large of a number...
    http://eng-serve.com/pic/pic_pwm.html
    #8
    bonedoc
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    Re:Random theoretical qustion about LED frequency 2011/01/05 11:35:03 (permalink)
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    Interesting. We have these lights that cops can use that will turn traffic lights green. Did not know if this was a specific color of light...IR...or what.

    I am also thinking about building a huge IR spotlight and getting a night vision camera. Been having some problems with trespassers. I wish I could design a thermal imager...but dont have a clue. I know they are too expensive to buy.
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    MBedder
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    Re:Random theoretical qustion about LED frequency 2011/01/05 16:51:34 (permalink)
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    The best solution to make a blue LED infrared is using a Doppler effect. You should take a blue LED in your hand and run with it as quick as possible LoLLoLLoL
    #10
    BobK
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    Re:Random theoretical qustion about LED frequency 2011/01/05 17:14:05 (permalink)
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    MBedder

    The best solution to make a blue LED infrared is using a Doppler effect. You should take a blue LED in your hand and run with it as quick as possible LoLLoLLoL


    Yep, half the speed of light should do nicely.  On the other hand, using an IR LED to start with would be slightly more energy efficient.
     
    Bob
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    bonedoc
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    Re:Random theoretical qustion about LED frequency 2011/01/05 17:38:37 (permalink)
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    MBedder

    The best solution to make a blue LED infrared is using a Doppler effect. You should take a blue LED in your hand and run with it as quick as possible LoLLoLLoL


    You failed to mention that I would have to be running away from the detecting source.

    But seriously, isnt this what "carrier bands" are in communications?

    A higher frequency wave that carries a lower frequency wave?
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    MarkT
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    Re:Random theoretical qustion about LED frequency 2011/01/05 18:56:27 (permalink)
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    All jokes, and impracticalities like 400+THz PWM engines [8D], aside I don't think the physics would work.  Light colour is set by the energy each photon holds, which in turn sets the wavelength of the light (more energy => higher oscillation frequency => shorter wavelength).  Just because you OOK modulate the blue light at a lower frequency doesn't mean you change the amount of energy in each photon, it just means that you're selectively emitting photons.

    non illegitimi carborundorum
    #13
    Ian.M
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    Re:Random theoretical qustion about LED frequency 2011/01/06 01:54:20 (permalink)
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    I don't think it is physically realisable using a LED and *IF* one could pulse a diode laser that fast there certainly wont be significant energy content in the infrared band.  (I wont say NONE as nonlinearities may result in a slight output at the difference frequency)  I know that the high energy optics researchers have got down to femtosecond pulses and below, so they are in the ballpark, but they aren't doing that by PWM!

    I reckon that carrier transit time considerations alone will prevent any modulation of a LED being effective well below 10GHz modulation frequency.  If it was *EASY* then 10MHz Video spec optoisolators would be *CHEAP* LoL
    #14
    DarioG
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    Re:Random theoretical qustion about LED frequency 2011/01/06 05:38:33 (permalink)
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    Well, interesting thread after all! Smile

    GENOVA :D :D ! GODO
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    kimonsp
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    Re:Random theoretical qustion about LED frequency 2011/01/06 06:11:20 (permalink)
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    OK, first of all:

    BSET    MOOD,SARCASM    ;Set the SARCASM bit (is this really necessary ?? =)

    @bonedoc: Now, changing the actual discussion subject a little bit, about your post #4, you should take care about your opinions online (this applies to us all, I guess)... I believe there is no reason, even if it’s just for a joke, to break the laws...
    For legislation reference, see HERE and, more specifically, HERE.

    That stated, you should, in order not to break the laws again, explain that you are in an IDEAL environment. This imposes vacuum and because of that, your drawing should be corrected, as attached...

    Thanks for letting me share my opinion... mr green


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    Kimon
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    bill190
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    Re:Random theoretical qustion about LED frequency 2011/01/06 09:47:02 (permalink)
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    bonedoc
    But seriously, isnt this what "carrier bands" are in communications?

    A higher frequency wave that carries a lower frequency wave?


    An IR remote control "carrier frequency" is typically 38,000 Hz. Or the IR led is being turned on/off 38,000 times a second.
     
    Then to send ones and zeros, you turn that signal on/off.
     
    Here is a web page which shows this...
    http://www.sbprojects.com/knowledge/ir/sirc.htm
     
     
    #17
    bonedoc
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    Re:Random theoretical qustion about LED frequency 2011/01/07 09:01:32 (permalink)
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    Believe it or not, I took thermodynamics at KU. I probably should have set looser standards on the question.

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    MBedder
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    Re:Random theoretical qustion about LED frequency 2011/01/07 10:28:20 (permalink)
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    Taking thermodynamics doesn't necessarily mean understanding it - your case proves this statement perfectlyLoL
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    bonedoc
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    Re:Random theoretical qustion about LED frequency 2011/01/07 12:14:39 (permalink)
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    Actually, it wasnt that I couldnt learn it. There was another barrier....

    My professor was from Russia and didnt understand English. grin
    #20
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