I Do intensity flickers result from the nature of EM waves?

  • Thread starter greswd
  • Start date
640
14
Since light intensity is proportional to the amplitude of the EM wave, and wave amplitudes undulate up and down, does this result in natural intensity flickering of observed light?

For visible light, the frequency is extremely high, but it might be more easily observable in ELF waves.
 
6,160
3,398
Good question, but no, For most humans, the limit for consciously noticing light flicker is somewhere in the range 30-90 Hertz. We have had discussions on that on PF. Some people see flicker at 50 Hz, but not at 60 Hz.

Compare that to visible light 430–770 THz. and you can see that there is a "tera" of difference.
 

sophiecentaur

Science Advisor
Gold Member
22,756
3,526
Since light intensity is proportional to the amplitude of the EM wave, and wave amplitudes undulate up and down, does this result in natural intensity flickering of observed light?

For visible light, the frequency is extremely high, but it might be more easily observable in ELF waves.
Well, yes, the EM energy travels in bunches, corresponding to the peaks of the E and H fields (which are in phase in an EM wave in space).
I had to read this a few times before I understood what you were saying. But it is perfectly possible (we do it every day) to observe / measure the variation of the E and H fields of an EM wave. I don't know the present upper frequency limit for directly observing the varying fields but the carrier wave can be directly observed on conventional 'home' test equipment up to hundreds of MHz - i.e. you can see the RF waveform varying in real time on an oscilloscope display. It's not something that's done very often because there are better ways (in receivers), involving frequency mixing, to beat such high frequency signals down to more convenient Intermediate (I.F.) frequencies.
You may be wondering about how fast common objects can actually vibrate in step with an EM wave. Quartz Crystals can physically vibrate 'in step with' an incident UHF RF signal but you need to provide a suitable circuit to get the EM energy to the crystal.
 
640
14
Good question, but no, For most humans, the limit for consciously noticing light flicker is somewhere in the range 30-90 Hertz. We have had discussions on that on PF. Some people see flicker at 50 Hz, but not at 60 Hz.

Compare that to visible light 430–770 THz. and you can see that there is a "tera" of difference.
Sorry, nothing to do with human perception, but about whether the intensity of EM radiation objectively flickers, and whether it can be observed with a camera built for detecting fluctuations with the frequencies involved.


..the carrier wave can be directly observed on conventional 'home' test equipment up to hundreds of MHz - i.e. you can see the RF waveform varying in real time on an oscilloscope display.
thanks, how low are those RFs that you can observe them varying in real time?
 

sophiecentaur

Science Advisor
Gold Member
22,756
3,526
thanks, how low are those RFs that you can observe them varying in real time?
Connect an antenna to a basic analogue oscilloscope which will show you a snapshot of the variations. The scope has the effect of slowing down the time in which the actual oscillations occur. I mentioned that this can be done for radio frequencies of up to several hundred MHz.
 
6,160
3,398
The question is still unclear. @sophiecentaur is responding for radio frequencies of up to several hundred MHz." whereas
the OP says
Since light intensity is proportional to the amplitude of the EM wave, and wave amplitudes undulate up and down, does this result in natural intensity flickering of observed light?

For visible light, the frequency is extremely high, but it might be more easily observable in ELF waves.
That sounds to me like you are asking about the undulations within a single photon. The lower end of the visible spectrum is about 430 THz.

Please clarify. Are you asking about
  1. a beam of light modulated at a lower frequency?
  2. or about the undulations at the frequency of the color?
  3. Or are you asking about ELF radio, which is EM radiation but which we do not usually call light?
 

sophiecentaur

Science Advisor
Gold Member
22,756
3,526
That sounds to me like you are asking about the undulations within a single photon.
Best not to go there, I think. Photons seldom help to make things clearer in these sorts of discussions because they are not like people feel they ought to be. The classical wave model is what's called for here.
 
Last edited:

Want to reply to this thread?

"Do intensity flickers result from the nature of EM waves?" You must log in or register to reply here.

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Top Threads

Top