Can someone please explain how energy is conserved when the photon is emitted? The valence electron passes from the n region to p region as a result of the voltage across the two regions supplied by the power supply-energy is conserved by producing a current (which is literally that transfer of the electron), makes sense. But when that valence electron emits the photon where does THAT energy come from? Is it being coming from the momentum of the electron as it is brought into orbit of an atom in the p region? Please explain... I cannot figure that part out. Amazing video!

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Thanks Garrett! I really appreciate that feedback, gives me a little pick-me-up for the day :-)

when i was in university i didn't have youtube, i didn't even have the time to open my computer

@@goldenbeardofficial8541 so what was you doing? 😂

"And then the cathodes and the anodes lived happily ever after."

Haha! That's awesome to hear! Yeah, EE can be boring in the wrong hands but I think we're fortunate that all of the engineers here at CircuitBread find it fascinating, which helps keep us motivated when things are challenging.

Glad it was helpful!

Awesome, that's good to hear!

Hi there! We actually have several videos on diodes - a higher level video on how they work as well as several videos on how they work at the semiconductor level. Hopefully they clarify things!

Yep! Exactly. Though the LEDs still emit a little bit of heat as well, just less than a regular diode.

You did't study that in high scoohl

Thank you so much for your feedback! Glad we can help!

Thank you! We're actually hoping, once we get more content up, to actively partner with colleges on some content so that students can have their in-class and our video/written tutorials work together. I don't know how well it will work out but that's something we're striving for.

Teachers can be hit or miss, unfortunately. But there are great teachers out there that do really care about students, you just have to find them. And hope they're not burned out by being overwhelmed by students who yearn for help. One of the greatest professors I had as an undergraduate went above and beyond and, even ten years after I got my bachelors, was willing to help us with a handful of these semiconductor devices videos, making sure they're accurate. Those are the type of teachers and professors I'm grateful for.

@@CircuitBread Indeed, however, mostly 'miss' in my experience.

You are absolutely correct, thank you!

Yes! This brings me a ridiculous amount of joy. I hope it was fun!

I know, it kinda blew my mind when I learned about this as well. Thanks for the feedback!

👍Awesome!

Yep, that was a question I had as well. What happens is that, since you have a voltage, those electrons drop into the holes on the other side of the PN junction and then those electrons (or, more likely, other electrons) eventually pop out of the holes again and work their way out of the semiconductor material to go around in a big cycle again. I recommend checking out our video on how a PN junction works to hopefully clarify this question.

You're right - it's when the electron goes into orbit of an atom in the p region, dropping in its orbital energy to do so. We say it "fills a hole" but the reality is that it's just dropping into the valence band, or, in other words, being pulled into orbit around a specific atom. The energy it loses from dropping into that hole is emitted as a photon, producing the light. Now, where I'm a bit sketchy and would rather have someone with a PhD or just better specialization in this field confirm, is that the electron *does* lose energy crossing the junction and getting onto the p-side, but then the electron loses *more* energy when it drops into orbit of the atom. I'll leave this out there if someone (including other engineers at CircuitBread) want to comment. Excellent question, thank you!

@@CircuitBread Thanks for the detailed response! That really clears things up for me. I do know that energy is conserved when the electron moves position as a result of the chain of electrons in the circuit simultaneously moving (that is, a current through the circuit) which takes energy from the battery. Think of a watering hose, if it is full of water (wire full of electrons) and you add some more water to it via a water supply (adding electrons to the wire with a CV source), water is immediately spilled out on the other end, thus the energy gained from forcing water into one end is conserved when water is spilled out the other end. Same concept with electron flow. With this in mind, I do not think that it is the individual electron loosing energy as it crosses into the p region, instead energy from that action is consumed in the battery as a new electron further down the line enters a charged terminal as another electron leaves the terminal of opposite charge.

@@greenief9097 can you please explain how electron energy is lowered when it goes to orbit around atom Since when electron is confined to move within an orbit it's Δ x is less, so Δ p should be more acc to uncertainty principle

@@CircuitBread can you please explain how electron energy is lowered when it goes to orbit around atom Since when electron is confined to move within an orbit it's Δ x is less, so Δ p should be more acc to uncertainty principle

@@pavanjoshi2448 Having taken a course on it since the time of my first reply, look into "potential energy wells." Specifically finite potential wells. It is a pretty abstract idea, and connects the wavelength of the electron to the energy it has. When the electron is passing from one atom to the next, it briefly inhabits free space. Think of a ball that has rolled down a hill and is resting at the bottom. But then, it comes within the vicinity of the next atom, and this is similar to saying that the ball now is near a ridge where it can fall down. As the electron falls into orbit, loosing the potential energy it had and gaining kinetic energy, it emits a photon of a specific wavelength to compensate for the energy change. This is not an in depth answer: look into potential wells!

nah, electrons can't be destroyed with this ease

Awesome!!

You're welcome, thanks for the feedback!

He predicted the existence of electromagnetic waves but I'm not sure who it was that actually figured out which wave lengths produce ultraviolet light...

Interestingly enough, we have shot a video about how a computer works from the ground up - starting with sand and talking about how that's turned into semiconductors which are then turned into logic gates, etc. While the video is completely shot, there are a few animated portions of it that are being time consuming. I'm not sure if this is exactly what you're looking for but we're quite excited for this video to be published. Whenever it actually happens...

This video explains on a molecular level how electrons flow. It also breaks down the doping process of pnp/npn transistors. kzfaq.info/get/bejne/gJqfgpqBucXSqoU.html

Yeah! It's all about the wavelength of the energy and how much of a drop in energy there is when the electron changes from one energy level to the other. This is actually how they have made LEDs of different colors - blue, a higher energy light, requires a greater energy drop of the electron than red light so they put together two materials where there is the appropriate change in energy level from one to the other. So, there are a few things going on here but if the electron drops a smaller step, like in a diode, the energy is in the infrared range and is trapped inside the device itself - heat!

@@CircuitBread Ahhh I see, interesting. Appreciate the reply. Great video btw.

Hey Amjad, I don't know but I have a theory I think is reasonable. The light emitting side is the cathode, so you want as much available surface area there as possible. However, a thin vertical bar would be pretty weak mechanically. So, by creating those two odd shapes, you're maximizing the surface area on top of the cathode while still providing enough mechanical strength to both the anode and the cathode to not be bent during the encapsulation process. A flaw in this thinking is that the wire between the anode and cathode is tiny and doesn't seem to be affected. Hmmm... I hope someone else that knows the answer will chime in.

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Our pleasure!

Hey Ben, we got a tutorial about that, go check it out here: www.circuitbread.com/tutorials/how-rgb-leds-work-and-how-to-control-color

@@CircuitBread thank you very much!

Combine RGB and increase or decrease intensity of either of those bulbs

Not that I'm aware of - unless I've missed some update in some basic physics (and I'm not saying that sarcastically, there are constant updates in the scientific fields) then the wavelength of the emitted light is directly tied to the materials used in the LED.

I had that same question when I first learned about this. My understanding is that once the electrons drop in energy, then they act like a "normal" electron in that material, which means they can later jump into the conduction band and be conducted out of the device to go around the circuit loop again.

No, not a dumb question at all, it's something I think all of us have considered at one point or another. My understanding is that it's just a matter of it being a true circuit - as the holes are filled with the electrons dropping into them, holes are forming elsewhere due to the energy being put into the system. The holes slowly move into place and replenish the lost holes. Since it's done constantly, there's never a real lack of holes. I need to reach out to my semiconductors expert again, she may have a more technically fulfilling way of describing it.

The larger the energy gap, the higher the knee voltage. You'll note this with LEDs of different colors. Different band gaps generate different colors, which is why LEDs of different colors have different band gaps. I'm not sure if there's a mathematical relationship between the two but I would be a little surprised if there isn't.

Why LEDs look the way they do with the dome? I think it's just a manufacturing standard developed years ago that was easy to make and didn't block any of the light coming from the light emitting portion itself. There are many, many different body styles now available.

@@CircuitBread thank you 🙏

We discussed it but we ended up deleting that from the script because we didn't think we could do it justice without getting too deep into the physics behind it. We could've been wrong about that assumption.

Sorry about that! In one of our RGB videos, it is mentioned that typically white is created by emitting a balance of all three colors. There is also a way of making a blue LED more white with some sort of coating but I'm not as familiar with that process as much. Creating white with the three colors is a lot more primitive yet widespread than you'd think.

I knew they emitted light, but I thought it was more in the red-infrared range. But yep, the opaque cover makes it so you can even see the little bit of light they do produce (under normal conditions). Thanks for sharing! It would've been cool to have gotten that on video.

It is pretty crazy technology! It's not the amount of doping, it's by putting two different materials together that, when an electron moves from one to the other, it loses the exact amount of energy needed to create a photon of the color you want. Most diodes just produce heat when the electron loses that energy.

Same exact concept but instead of the cup portion shown in this video, the yellow portion acts the same as that cup, emitting the light.

I disagree, you aren't doing anything wrong - the battery WILL absorb the photon energy. A photo diode is, in essence, just a small solar cell. Depending on the setup, the current generated by the photodiode may go back into the battery or it may go elsewhere in the circuit. If the battery is non-rechargeable, hopefully it won't be going back into the battery but, at the same time, the amount of current these small photo diodes create are extremely small and probably non-problematic.

Thank you very much

This video explains on a molecular level how electrons flow. It also breaks down the doping process of pnp/npn transistors. kzfaq.info/get/bejne/gJqfgpqBucXSqoU.html

@@CircuitBread I'm not trying to take away from your lecture, I thought it was great. New sub

Exactly! The LED is optimized to create light from power and a solar cell is optimized to create power from light but practically, it's the same thing happening in reverse.

Cool, I was deducing the same thing too recently!

That would be pretty amazing!

A chemist or an expert in this field might take umbrage at the details or verbiage, but yes, that's a solid understanding of what's going on!

Many thanks for the response. Your videos are excellent and have been a massive help. 👍🏼

This video explains on a molecular level how electrons flow. It also breaks down the doping process of pnp/npn transistors. kzfaq.info/get/bejne/gJqfgpqBucXSqoU.html

I think they get filled by the power source ie; Battery or outlet.

This video explains on a molecular level how electrons flow. It also breaks down the doping process of pnp/npn transistors. kzfaq.info/get/bejne/gJqfgpqBucXSqoU.html

Sorry, what's a KTU syllabus? I'm getting "APJ Abdul Kalam Technological University" from a google search. We actually are trying to create our newer series to be more in line with general electronics syllabi but there's always going to be variations...

@@CircuitBread yaa its that itself 🙂 Thanks alot for the reply I never expected you would reply ❤️

Not really... as they're not designed for that, they could burn out open or burn out closed, which means that they could make the situation even worse. There may be fuses that incorporate LEDs to indicate their status - I haven't heard of that but there's a lot of things that exist that I haven't heard of.

I'm not sure, actually. My guess would be something yellowish-green.

LEDs, given a constant voltage, will give out a constant light. While the photons are discrete, there are so many of them, there is no way our brains could distinguish each one. On the other hand, a common way of dimming LEDs is exactly that method. They flicker the LEDs on and off fast enough that our brains can't register that they're flickering but instead interprets it as simply being dimmer. I have seen where they've flickered the LEDs too slowly and it gives a very subtle, nearly subconscious, strobing effect that is quite unpleasant.

@@CircuitBread damn, i hoped i was wrong. So you are agreeing, the led may appear less bright than it actually is, due to your brain merging the bright flash with the dark inbetween. I wonder if this means the retina or other sensitive parts of the eye may be more easily damaged by this LED light as the light is maybe brighter than the retina or optic nerve is percieving it.

I've wondered about that myself - it seems like if the flash were bright enough, even if the duration is incredibly short, then it would cause some damage.

I'm sorry, I don't really understand, could you rephrase what the LED lamp is doing?

@@CircuitBread my new lamp At night I close it When I look at it on the roof it's off course I see a little light like a small dot After some time it finishes I got scared

Hm, interesting. Strangely, LEDs are so efficient that they can emit a very small glow with small amounts of residual charge or stray voltage. While this can cause a glow to last a ridiculously long time (minutes), it is common for LED bulbs to take several seconds to wind down to a level that you can no longer see them.

@@CircuitBread Thank you very much indeed for your valuable explanation. This explained for me the issue Grateful.

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LEDs emit unpolarized light but most all of them contain trace amounts of lead and arsenic. The quantities of these materials are extremely small, though, and while not ideal, is generally much more environmentally and biologically friendly than many other options. That is assuming you're using high-quality LEDs from a reputable source - some LED manufacturers may be less focused on following environmental regulations. In regards to UV, unless the LEDs are specifically designed to emit UV, their emissions in that spectrum are minimal to non-existent. That's one reason they're popular as outdoor lights - their limited heat and UV output makes it so they don't attract bugs like incandescent bulbs do.

@@CircuitBread Thank you so much; your reply gave me much relief... I was so worried... Not anymore though. Bullish on LEDs now; YOLO!

Dang, that sucks. Good thing you tested them!

@@CircuitBread I bought some more but, from a different vendor... And they worked great 😃

That's mind blowing! 😮

I think that these fields will become more stratified and specialized. I think there will always be people who need to know the electron/photon theories so they can improve the underlying technology, while others will be focused on sourcing and purifying materials and fabrication methods. Just like Arduino has made it so that many people can jump right into embedded systems with limited electronics understanding but we still need the people who create the Atmega processors the Arduino is built on, as well as the library the IDE is built on.

Thanks for the feedback! Could you let me know exactly which symbols were flipped? I only see three in the reference table and I *think* they're right. I appreciate you keeping us honest!

@@CircuitBread oh my lord i'm an idiot, hahaha. nevermind!

The more of these videos you watch, the more you will believe me when I say, "No worries, I do that sort of stuff ALL THE TIME." 😂

I've heard this concern and have even read a research paper about it that seemed inconclusive. I'm not a biologist or a doctor, so I can't say anything definitive on the physiological side. But, from an engineering point of view, I haven't come across anything that would make the think that LED technology is inherently worse for the eyes.