How do LED generate photons and heat?

Like someone said earlier.. I was thinking, which can be dangerous.....

I think I understand how LEDs generate light and heat, but would like an explanation from someone who knows for sure.

I am guessing that electron flow somehow causes atoms to jump to higher energy states, and when they atoms decay back, they give off photons. Heat is not part of this process, but mearly generated by electrons passing through the medium and not being absorbed by the light emitting atoms.
I remember hearing about 'holes' that force electron flow, but I dont recall what that was all about.

Now, I may be WAY off, but it sounds good.

Jeff

You're REALLY close, Jeff. It's the electrons within the atoms that jump to higher orbits, then decay back to their resting state and release energy (photons) when they do that.

The heat that's produced is from the normal less-than-100%-efficiency of the whole process, including resistance within the electrodes.

Somebody stop me if I start making sense! /ubbthreads/images/graemlins/yellowlaugh.gif

"It's the electrons within the atoms that jump to higher orbits",, thats what I ment... you mean I was right.. WOW

Jeff

Thats the Niels Bohr model, which more or less analogizes an electron's orbit with that of the moon orbiting the earth. Contemporary brainiacs say that an electron is more like a wave than a particle, i.e., that it exists in particular states of energy rather than jumping from orbit to orbit. I think (know) that they are still in the Middle Ages in terms of actually knowing what they are talking about, since they don't actually know what an electron is, what a photon is, or how one magically springs from the other.

So, I think the best answer to your question about how an LED produces light is that no one really knows. Ain't it mindbending?

/ubbthreads/images/graemlins/ooo.gif /ubbthreads/images/graemlins/happy14.gif

best regards

WildRice -

I guess it's pretty clear you got a perfect responder. I mean, how can you wrangle photons if you don't know how they are calfed?

It sounds like you had it figured pretty well.

I think heat may be generated because not all the excited electrons from the p-doped semi-conductor meet up with holes from the n-doped semi-conductor and those unmatched, excited electrons create heat.

I was composing while powernoodle was posting. I've read on CPF and elsewhere exactly what he's talking about. It is mind bending. How can particles be waves? AIUI, powernoodle explains it perfectly. The wave is in a particular state so it is a wave and a particle. I don't really totaly get it but I kinda get it and I like thinking about it. It helps me to understand rays and why one type of ray acts differently than other types of rays.

Here is a previous discussion that includes holes. How do LEDs work?

In that discussion, I gave a link to a college primer that included a cute little java applet. In that simple graphic, inefficiancy is not represented. You can play with two controls for chemistry and voltage.

Maybe I'm easily entertained?

- Jeff

OK, that "explains" the physics of it, how about the physical? Such as, I know how an incandescent bulb makes light; It heats up a filament until it glows, effectively being white hot. What's the doohickey in an LED that makes the light without being white hot? (I think)

it is basically an ineffiecent form of energy transformation. Using a flow of electrons (energy) to force a material to be 'charged', the material dosent want to be charged, so it sheds the energy that was forced into it, the energy it gives off is a photon, or particle of light.
How bouts that...

Jeff

The most important thing to know for LEDs is that they consists of two separate parts. One has an excess of electrons, the other a lack thereof. One can think of the missing electrons as positively charged holes. The electrons reside at a higher energy level than the holes. When the voltage is applied, the electrons and holes are pushed together into the same regions so that the electrons can fall down into the holes (recombination), which results in light emission. Because the electrons are already at a higher energy level, we don't need high temperature to raise them from a lower level, as happens in a hot metal filament.

The semiconductor forming the LED is not a very good conductor. The electrons (and holes) have to act against the resistance, resulting in heat.

*edited.* elgarak's two material explanation is more accurate than mine was.
*second edit.* as explained in his post below. Thanks, elgarak.

5mm doohicky from microscopy.fsu.edu:

Minor correction: There is only one type of electrons, and all electrons are negative. The positive charge comes from "missing" electrons. However, those holes essentially behave like positive charged particles.

This graphic shows the energy levels in an LED with and without applied voltage ("bias"). This movie visualizes the light emitting process; howver, they skip the shifting of the energy levels with voltage.

You could learn about quarks, flavors, stranges, and spins, as was established over 20 years ago (the pieces that make up particles like electrons, protons, positrons, etc.), and also about sub-orbits. Since then, things have been defined a little better, bringing in strange, charm, and other interesting things.

Start here for the high school basics on what make up particles:

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/quark.html

Good suggestion, Jar. I think I really need a smaller submarine for that fantastic voyage. I don't quite get the quark universe but I like trying to get it.

Check out PBS for a program called "The Elegant Universe" or buy the book....which is in more depth and will really tax your mind.

Did you know life savers of the pepperment flavor can generate photons too when chewed with your mouth open?

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cobb said:
Did you know life savers of the pepperment flavor can generate photons too when chewed with your mouth open?

[/ QUOTE ]

Yea, the piezoelectric effect. I forget if it's peppermint or wintergreen though.

[ QUOTE ]
powernoodle said:
Contemporary brainiacs say that an electron is more like a wave than a particle, i.e., that it exists in particular states of energy rather than jumping from orbit to orbit. I think (know) that they are still in the Middle Ages in terms of actually knowing what they are talking about, since they don't actually know what an electron is, what a photon is, or how one magically springs from the other.

So, I think the best answer to your question about how an LED produces light is that no one really knows. Ain't it mindbending?



[/ QUOTE ]

Actually both are used to describe electrons in 'the real world'. They have established physical size and mass (something waves don't) and (when in motion) interact with each other like waves as well as having other 'wave like' natures (like wavelength, for instance). All are fairly well understood, I think I can safely say for the majority of us that deal with this on a daily basis we hardly consider ourselves to have a "middle ages" understanding.

And as to how quantum mechanics works WRT LEDs producing light, I again have to differ, there are a lot of folks out there who *intimately* understand it and design new materials around that understanding, it is far, far from 'nobody really knows'.

For sure it's past some to understand, but I know (and work with) a pile of folks who do. It's not mindbending, but it does take some dicipline and understanding to 'get it'.

These things are simply not done by guess work. Rather solid science.

Doug Owen

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PhotonWrangler said:

Yea, the piezoelectric effect. I forget if it's peppermint or wintergreen though.

[/ QUOTE ]

Wintergreen.

Doug Owen

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Doug Owen said:
[ QUOTE ]
PhotonWrangler said:

Yea, the piezoelectric effect. I forget if it's peppermint or wintergreen though.

[/ QUOTE ]

Wintergreen.

Doug Owen

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I can see the headline on Tuesday -
"There was an unexplained run on Wintergreen LifeSavers yesterday..."
/ubbthreads/images/graemlins/crackup.gif

I used to process my own B&W film many moons ago. I still remember that when I would peel the masking tape off of the end of a roll of film in the darkroom, there would be a brief greenish flash when I did it. I don't remember if it was the tape or the film that produced the flash.

Another piezoelectric quirk -

I was attending a home entertainment systems demo one day where they had a high-powered speaker sitting on a small end table. The table had clear lucite legs and it was sitting on a thick carpet. Whenever the music hit a loud portion, the table legs would flicker from the energy! And this was actually visible in room lighting. There was a long line of people waiting to get into that demo room, not to see the stereo system, but to see the furniture lighting up from the energy! /ubbthreads/images/graemlins/cool.gif

Next power failure, just spray your mouth silver and buy a roll or life savers and chew with your mouth open /ubbthreads/images/graemlins/smile.gif