[evan_au]

LEDs don't give single spectral lines, but lasers (nearly) do.

To add to bored chemist's comment:
- Red LEDs and Red LASERs can be made from similar semiconductor materials
- But laser chips have a parallel mirrors on each end, so that most of the light bounces back and forth within this laser cavity; where an integer number of wavelengths fit in the cavity length, the oscillation is self-sustaining, while other wavelengths rapidly die out. This means that the spectrum from a laser chip is much more monochromatic than light from a LED.
- Since the cavity is much longer than the wavelength of the light, it is possible for there to be n, n+1, n-1 etc wavelengths of light in the length of the cavity. These are called different "modes" of the laser.
- As temperature changes, different modes are favored. So a monochromatic laser needs temperature controls.
- Under some conditions, the laser can randomly switch between adjacent modes - this is called "mode-hopping"
- Under other conditions, the laser can chaotically switch between many modes, producing a spectrum with several wavelength peaks
- For high-precision applications, an additional cavity is used to select just one of these modes

See examples here: https://www.newport.com/medias/sys_master/images/images/h4b/h48/8797049585694/AN08-Mode-Hopping-in-Semiconductor-Laser-Diodes.pdf

[mxplxxx (OP)]

Can anyone point me at a picture of Energy being integrated over time to give Planck's constant h? Preferably with different values of E and t. Frustratingly, I cannot find one on the internet.

[mxplxxx (OP)]

some people still need convincing that E = hf,

From my travels it would seem that this is mainly controversial when E is the energy of a photon. There appears to be little consensus amongst physicists regarding the nature of a photon. Iittle wonder then that laypeople like myself are totally confused and attempts at better theories are constantly being proposed. Here is one that does a fair job of marrying a photon and an EM wave, especially from a relativistic perspective.  http://vixra.org/pdf/1609.0359v1.pdf

[alancalverd]

E = hf is Planck's definition of h. How can that be controversial?

Regarding integration: Way back in the dawn of time I built a calorimeter to measure the energy deposited by photons emitted from a cobalt-60  source.  The integration time was around 100 seconds, and knowing the activity of the source and the solid angle covered by the calorimeter (plus a whole lot of corrections you can find in the textbooks), we could calculate the number of photons involved. It became the first UK national primary standard of absorbed dose for radiotherapy.

I don't think there is any doubt about the "nature" of a photon. It is what is emitted when a charged particle accelerates or changes state. The only confusion arises in the minds of people who confuse a mathematical model of a photon with an actual photon, because there are two useful models.

Back to the philosopher's favorite animal - the cow. There is no doubt as to the nature of a cow. Just like photons, you can see some of them. You can model a cow in terms of various ratios: grass input to milk output (a useful model of a live cow) or gross weight to edible pies (a useful model of a dead cow), but neither model tells you "what a cow is".

[mxplxxx (OP)]

As with Newtonian physics, relativity distinguishes between constant speed and acceleration.

Maybe the theory excludes acceleration because it invalidates the theory? Also, easy to point to time as the culprit when the theory doesn't work but not possible to explain away photon emission between two particles that think they are at rest even when seen to be accelerating by other particles.

[mxplxxx (OP)]

The only confusion arises in the minds of people who confuse a mathematical model of a photon with an actual photon, because there are two useful m

A perennial problem in physics!

[Bored chemist]

From my travels it would seem that this is mainly controversial when E is the energy of a photon.

It may seem that way to you.
There's still debate about the nature of the photon. (More about terminology than about how it behaves)
But none at all about the energy it carries.

[mxplxxx (OP)]

But none at all about the energy it carries.

There should always be  a question mark about E-hf for a photon until E can be measured directly:)

[Bored chemist]

But none at all about the energy it carries.

There should always be  a question mark about E-hf for a photon until E can be measured directly:)

There was a question.
And then it was measured. (the thread has given various examples of how this was done)
And now we have the answer.
So what are you banging on about?

[alancalverd]

As with Newtonian physics, relativity distinguishes between constant speed and acceleration.

Maybe the theory excludes acceleration because it invalidates the theory? Also, easy to point to time as the culprit when the theory doesn't work but not possible to explain away photon emission between two particles that think they are at rest even when seen to be accelerating by other particles.

Relativity does indeed deal with acceleration. Particles don't think. You would be well advised to learn some basic physics before pontificating on the subject.

[mxplxxx (OP)]

As with Newtonian physics, relativity distinguishes between constant speed and acceleration.

Maybe the theory excludes acceleration because it invalidates the theory? Also, easy to point to time as the culprit when the theory doesn't work but not possible to explain away photon emission between two particles that think they are at rest even when seen to be accelerating by other particles.

Relativity does indeed deal with acceleration. Particles don't think. You would be well advised to learn some basic physics before pontificating on the subject.

"Maybe" is hardly pontificating. It is inviting an opinion which you have given. Lots of people think differently. Maybe you could supply references.

[alancalverd]

you can't "validate" E = hf because it is the definition of h.

Actually, you can. There are other ways of measuring h
https://en.wikipedia.org/wiki/Brownian_motion#Einstein's_theory
https://en.wikipedia.org/wiki/Noise_temperature

I was so intrigued by your statement that I read both articles. Neither mentions Planck's constant. The symbol h appears in the first article, but means barometric height, not action.

[esquire]

photon are massless, they have no charge, they do have spin
yet photons have energy. this qualifies photons for not having a zero rest state, contradiction?
a charge references a particle state. a particle because of mass is energy.
a photon because of zero mass shouldn't qualify it as having energy.
charge and energy are two different things. without charge energy does not exist but charge can exist w/o energy.
 
Mass = energy, energy requires a charge. without a charge particle, energy cannot exist within that particle.  this is a contradiction for a photon, without a charge state, energy is null.

does a particle have a wave frequency? the uncertainty principle states either location or velocity can be determined, approximately. a particle traveling at the speed of light, can be located within a strictly short locational proximity. the particle moving at the SOL appears to be at both ends of the short locational boundary and all points in-between.  In this short locational boundary there has been no observance of a wave of any intensity or frequency. the observed particle is between two points and all points in-between. this doesn't resemble a wave with the characteristic undulating of frequency. the observance is flatlined.

so e=hf, mass = planck x frequency. with zero frequency, planck is a useless multiplier when it comes to the measurement of photonic energy . e=hf, most definitely has application in most arenas, just not with measuring the energy of a photon.

[Bored chemist]

you can't "validate" E = hf because it is the definition of h.

Actually, you can. There are other ways of measuring h
https://en.wikipedia.org/wiki/Brownian_motion#Einstein's_theory
https://en.wikipedia.org/wiki/Noise_temperature

I was so intrigued by your statement that I read both articles. Neither mentions Planck's constant. The symbol h appears in the first article, but means barometric height, not action.

Bother!
I got my constants muddled

Fortunately, there are still plenty of ways to measure h
https://en.wikipedia.org/wiki/Planck_constant#Determination

So, my point's still valid.

[jeffreyH]

The beginnings of quantum mechanics were very mundane. It was Planck's intention to solve a problem for experimenters. Read the story here https://www.google.com/amp/s/amp.theguardian.com/science/2000/dec/14/particlephysics

[mxplxxx (OP)]

That is correct. There is no good way to directly measure the energy of a single photon.

Why is that?

No answer to this, so I will have a guess. I would say that nothing that moves at the speed of light can be measured. According to relativity, time does not exist for such an object which would likely complicate any attempt to measure it. It seems to exist only in the present (which roars by at the speed of light!), with no past or future. Given that our experience of the present is dependent on photons, this makes sense.

Note also , the fact that time does not exist for a photon means also that it cannot "wave".  How then does it appear to exist as an EM wave? Imho, relativity needs to be updated to account for this situation. One possibility is that the wave exists in the future which makes sense given that the photon seems to exist initially as a possibility wave:)

[jeffreyH]

One last try at punching smoke. The ultraviolet catastrophe was solved by Planck introducing h. Otherwise the classical theory would still predict the energy approaching infinity at shorter wavelengths. https://en.m.wikipedia.org/wiki/Ultraviolet_catastrophe

If you still don't understand then there is no hope.

[mxplxxx (OP)]

One last try at punching smoke. The ultraviolet catastrophe was solved by Planck introducing h. Otherwise the classical theory would still predict the energy approaching infinity at shorter wavelengths. https://en.m.wikipedia.org/wiki/Ultraviolet_catastrophe

If you still don't understand then there is no hope.

What is this in reference to?

[evan_au]

the uncertainty principle states either location or velocity can be determined, approximately.

There are several versions of the uncertainty principle.

But if you are only interested in the energy of the photon, and don't care too much about the position at which it arrived, or the time that it arrived, then you can measure the energy moderately accurately, even for (80% of) single photons.

Astronomers use CCD detectors that:
- Have a large fraction of the surface area available for detecting photons; the remainder is covered by wires, and some photons will be reflected rather than absorbed. Something like 80% of incoming photons can be detected.
- Are cooled to low temperatures, so there is a very low "dark current", and few spontaneous detections where there was no incoming photon (ie a "false alarm")
- Can be coupled to a large-area diffraction grating, which splits light into different wavelength/energy bands. There are several locations that a photon of a given energy could arrive, but if you put a CCD at all of them, you can estimate the energy regardless of where it arrives.

For this to work well, the energy of the incoming photons needs to be constrained within a reasonable range, otherwise a photon could be confused with one of a much higher or lower energy.
See: https://en.wikipedia.org/wiki/Charge-coupled_device#Use_in_astronomy
https://en.wikipedia.org/wiki/Diffraction_grating
 

[alancalverd]

Somewhere ikn the last 50 years, I forgot about the GeLi gamma spectrometers we used to use to calibrate x-ray sources. Wikipedia has a good explanatory article that I won't repeat here, but the key is that you can use a gamma emitter with a narrow spectrum to locate a single point on the resultant spectrum and thus measure the energy of any photon against your calibration point.

Getting down to single photon detection with GeLi is a bit of an art form but since we know photons are indistinguishable, if we find a narrow line on a spectrum we can say that it does at least represent the average energy of a few photons.

It's interesting that the questioner persists in telling us that something can't be done, in the face of the experience of those who have done it for a living.  Unshakeable faith in one's prejudice can be dangerous, but as a forlorn gesture of friendship I'll advise people not to play with fire or walk in front of moving buses.