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I am having a difficult time to understand how an infrared sensor and led work. I have an infrared LED (like the ones you buy anywhere), does it mean that the infrared LED has the frequency os 38khz?

I know that infrared light has a wavelegnth, but does it also have a frequency?

Samul
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    Frequency and wavelength are the same thing. This isn't an Arduino question, it's an incredibly basic Physics question. Answered here: http://en.wikipedia.org/wiki/Frequency#Frequency_of_waves (frequency x wavelength = velocity) – Jasmine Nov 23 '14 at 15:47
  • it's arduino question cause I am using an infrared sensor in arduino with 38kHz. If the speed is different then the wavelenght can have different frequency. JRobert cleared this to me. – Samul Nov 24 '14 at 01:58
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    No, it's really not. You're asking about the wavelength and frequency of the LED itself, which is not 38kHz. Infrared frequencies are in the 300GHz to 430THz range. That's the frequency of the light itself. The frequency of the electrical signal you send to the LED to light it at various brightness levels has nothing to do with that. The LED doesn't have a frequency other than the frequency of the light it produces. You're getting that confused with the frequency of the POWER SUPPLY to that LED. – Jasmine Nov 24 '14 at 16:19

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An infrared LED just emits its light (primarily) in the infrared range as described by this Wikipedia article. Any emitted radiated signal (including sound) has both a frequency and a wavelength. The frequency = the velocity of the signal through space divided by its wavelength (F = V / W), or vice-versa: (W = V / F). The natural frequency of light, infrared or visible is far, far higher than 38 KHz; around 4 x 10^14 Hz.

38 KHz is simply a convenient chopping frequency for switching the LED on and off so the sensor can distinguish between infrared in sunlight, for instance, which is relatively constant - from that emitted by the LED. Your circuitry would have to create the 38KHz chopping signal.

JRobert
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  • Awesome! :) So you mean that the speed of infrared, x ray and visible light is the same? The speed in which the wave travles is the same? – Samul Nov 24 '14 at 01:58
  • YES! Light waves/particles travel at the speed of light, which is a constant of the universe and is the same everywhere. Please educate yourself about "Electromagnetic Spectrum" here: http://en.wikipedia.org/wiki/Electromagnetic_spectrum – Jasmine Nov 24 '14 at 16:21
  • @Samul: Yes, with the exception that I also referred to the speed of sound. The velocity of sound in air is much, much slower but the principle will be the same. – JRobert Nov 24 '14 at 17:24
  • You helped me a lot! – Samul Nov 25 '14 at 00:05