What is Leds: Definition and 103 Discussions

A light-emitting diode (LED) is a semiconductor light source that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresponding to the energy of the photons) is determined by the energy required for electrons to cross the band gap of the semiconductor. White light is obtained by using multiple semiconductors or a layer of light-emitting phosphor on the semiconductor device.Appearing as practical electronic components in 1962, the earliest LEDs emitted low-intensity infrared (IR) light. Infrared LEDs are used in remote-control circuits, such as those used with a wide variety of consumer electronics. The first visible-light LEDs were of low intensity and limited to red. Modern LEDs are available in visible, ultraviolet (UV), and infrared wavelengths, with high light output.
Early LEDs were often used as indicator lamps, replacing small incandescent bulbs, and in seven-segment displays. Recent developments have produced high-output white light LEDs suitable for room and outdoor area lighting. LEDs have led to new displays and sensors, while their high switching rates are useful in advanced communications technology.
LEDs have many advantages over incandescent light sources, including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. LEDs are used in applications as diverse as aviation lighting, fairy lights, automotive headlamps, advertising, general lighting, traffic signals, camera flashes, lighted wallpaper, horticultural grow lights, and medical devices.Unlike a laser, the light emitted from an LED is neither spectrally coherent nor even highly monochromatic. However, its spectrum is sufficiently narrow that it appears to the human eye as a pure (saturated) color. Also unlike most lasers, its radiation is not spatially coherent, so it cannot approach the very high brightnesses characteristic of lasers.

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  1. L

    Combining Identical LEDs: Power Increase or Not?

    Hello, I was wondering if anyone know the physical explanation about the following: What happens if I combine two Identical LEDs with the exact same spectral profile (eg 350-450nm with 400nm center wavelength and peak). Assuming the total power of each LED in watts is 300mW. Will...
  2. S

    Wiring 100 LEDs - Advice Needed

    Hi I am making a project in my spare time and i am getting quite confused with the whole situation. I have 100 LED's that need to be wired up, my first question is what is best to wire them up in, series or parallel? My power source is a 9V alkaline battery and i need to know if a...
  3. C

    LEDs and Solid State Devices: Lifespan Explained

    Why do LEDs and other light emitting solid state devices have a definite lifespan?
  4. P

    Finding Planck's Constant with LEDs

    Homework Statement I am trying to prove Planck's constant using LEDs. So far I have measured several LED's wavelengths using a spectrometer and from this their frequency. This will be f in the equation h = E/f. For E I put the LEDs in a forward biased circuit and am trying to use the...
  5. J

    Need assistance building sound controlled LEDS

    I am building a moving target system for a shooting range. It will have a 40 foot target moving perpendicular to the shooter. I have not had any problem with fabricating the target system, but I want to go above what the customer requires. Hopefully this lead to more work for myself in the...
  6. F

    Why are blue LEDs so expensive?

    Why are blue leds so much more expensive than any other colour leds? I could buy a pack of 100 red leds for about $10, and 1 blue led for $4, in Sydney Australia. Does it have anything to do with the frequency of blue light being higher than green, red and yellow?
  7. C

    Easy Electronics Project with LEDs

    Well I don't know if this is the right place to do this question. I want to do a project of my class of electronics, and my circuit must contain at lest one intagreated circuit, can somebody give an easy one? It must contain just a integrated circuit and also something with LEDs. I am just a...
  8. I

    Forward Voltage / Dropped Voltage / LEDs

    Hiya, A co-worker and I were a little bored at work the last week and stumbled our way into playing around with basic circuits. Long story short we have made several simple series and parallel circuit diagrams and we practice working out the math and voltage drops across resistors and what...
  9. J

    Create Sound-Activated LED Circuit: Subwoofer & Floor Speakers

    So I was wondering how to create a sound activated LED circuit for each of my speakers. I want the red LEDs to light up when the subwoofer is activated and the blue LEDs to light up when the left and right floor speakers are activated. I had a thought about wiring the LEDs parellel to in input...
  10. D

    String of LEDs in parallel w/correct resistors and a TIP31 Transistor.

    I have a string of leds hooked up together with the correct resistors in parallel, going out to a TIP31 transistor which then goes to the power cord and to a 3mm jack. This 3mm jack goes into my computer and my leds "dance" to the music, I assume is the change in voltage. Anyways, I have...
  11. A

    LEDs for Growing Indoor Plants: Efficient Luminous Efficacy

    I'm a grade 9 student working on s a space design contest. For my project I'm using leds to grow indoor plants. i read that the most efficient leds for growing plant is 660, 615 and 461 nm. does anybody know the luminous efficacy of efficient leds of these types. any suggestions would be helpful...
  12. M

    Help with IR LEDs: Powering, Wiring & Resistor Questions

    I have a project in mind that I need help with IR LEDs. I'm not an electricity expert; actually, I have almost no experience in electronics. I had an idea for a project and now I'm just trying to make it work. I will need to power a number of IR LEDs at one time for a continuous period. Is...
  13. M

    LEDs on Batteries: How to Measure Voltage?

    Hello everybody, I tried to make a special LED I <3 you gift for my girlfriend and it seems that I failed to take into account the battery discharge curve. I was using 50 red LEDs that I originally measured with my voltmeters LED function at 1.7v. With measuring LED voltage, is it better...
  14. DaveC426913

    How can I wire up an LED puck light to an AC power source?

    OK, here's what I'm doing: I currently have a single 20 watt halogen puck: [PLAIN]http://www.lightingfx.com/media/images/product_category/ro29.jpg powered through a rectifier from AC. The reason I've done this is because I need the interrupt the AC with a light timer switch. I want...
  15. W

    ( easy ) Powering LEDs off of triple A batteries

    Okay, this is obscenely easy and that's why I'm confused on it. http://teachwithtech.com/Full-Product-Listing/Vishay-TSAL6400-10-Pack-p21.html What I'm trying to do is power two of those LEDs off of a single triple A battery, if at all possible. I don't know what the specifications mean. I...
  16. J

    Photodiodes vs LEDs: Gallium Arsenide Sensitivity

    Would a gallium arsenide photodiode be sensitive to light from a gallium phopsphide LED?
  17. V

    LED Intensity: Voltage & Band Gap Theory

    Hi guys, first post here but I have been looking around a while and this forum has proved to be pretty helpful. I have a question about LEDs. I just did a lab in school where I cooled LEDs by placing them close to liquid nitrogen and also heated them close to hot water and measured their voltage...
  18. G

    Designing Circuits with Multiple LEDs and Different Voltages?

    I know there are already a number of posts in this general subject area, but they all seem to involve circuits with one or more identical LEDs. I'm trying to come up with circuits containing red (approx 2.5 Vf) and blue (approx 3 Vf) LEDs that will run off a 2AA (3V) battery harness. I'm...
  19. S

    Circuit questions (polarity and LEDs)

    I'm going to go under the assumption that whatever I say is right, even though I know it's probably wrong (it saves me phrasing the entire thing as dozens of questions that way), so... correct me where necessary: If I have a +X volt battery and I connect it up to a circuit with an LED in it...
  20. J

    How Can I Safely Wire 100 LEDs Using a PS3's 120VAC Power Supply?

    im trying to wire 100 leds into my playstation using my ps3's 120vac power supply I am new to this so I am not quite sure how to do it but i found a night light wiring diagram and was wondering what i had to do to modify it to fit my needs i attached it to this post i appreciate any help thanks
  21. N

    25 Leds, 9V battery, which resistors to use?

    I'm wiring together 25 rgb leds, each take 3V and I was wondering what would be the most efficient way to wire up as many as possible off one power source using resistors. Which resistors should I use? Series or Parallel? 9V or 12V battery? This is for a small project I'm working on myself...
  22. U

    Radio-Emitting LEDs: Can It Be Done?

    As the title may suggest, I am in search of a LED that emits radio waves. Yes, radio. I have seen and heard of the wide spectrum of waves LEDs can produce, ranging from ultraviolet to infrared LEDs, but never of anything beyond that, for say, radio waves. Of course, it may sound as stupid as...
  23. I

    LEDs different colours and their forward(working) voltage

    Homework Statement hi I've just been doing labs today on data aquisition looking at current voltage characteristics, one thing that i did was look at the forward(working) voltage for a red, green and white LED. Red = 1.5V Green = 1.8V White = 2.6V when i asked the demonstarter why...
  24. W

    Modulating super bright LEDs helpplease

    OK...I am a total noob when discussing anything electrical...I am more at home in the mechanical side of life. Sorry...lol What my project is...is I would like to replicate a modulating headlight from a motorcycle by using very strong, bright LEDs. I ride a bike and used to use the halegen bulb...
  25. U

    Exploring the Role of Silicon in LED Functionality

    Why don't silicon diodes emit light? Attempt: No idea. However, I do know that gallium arsenide is used as a semiconductor in LEDs.
  26. N

    Powering 150 LEDs with a 12v,1A Power Supply

    I am trying to figure out a better way to power 150 leds that need 3.4v and 20mA with a 12v,1A power supply. Right now the best way I can think of is have 3 leds in series and a 100 ohm resistor at the end(50 times). Is their any better way so I can use less resistors
  27. D

    Are LEDs and Photodiodes Interchangeable in the Photoelectric Effect?

    So what has to be right for a metal to release electrons when shot with a light? if you use more than what's needed will it still work? can this be used to power something? what else should i know about it? I want to buy some 5mm LED bulbs to mess around with. from my understanding you can make...
  28. F

    Behaviour of LEDs in presence of magnetic fields?

    Behaviour of LEDs in presence of magnetic fields?? How do LEDs behave in presence of magnetic field?? Any good books or papers dealing extensively with this?? thanking in advance..
  29. H

    Lumens, candelas & equivalent LEDs

    I'm trying to determine the millicandela rating of an LED from a keychain to find equivalent LEDs of different colours. The keychain LED specs are as follows: Luminous Flux value: 4 lumens (from box) Viewing Angle: 30° (I got this value by comparing to LEDs with marked angles) Wavelength...
  30. R

    The production of LEDs using PLD

    I am curios about the production process of LEDs, particularly using the method of growing the crystal using CVD. I am not exactly sure where the best place is to start but here goes my first question. The refraction of SiC is as such that the light gets largely reflected back into the...
  31. Topher925

    Pushing LEDs Beyond Ratings: Can My 25ma LED Survive?

    How far can you push most LEDs beyond their recommended rating before they burn out? I currently have a 25ma, 34k mcd LED that I am planning on putting 50ma through for 10ms durations for 30ms periods. The LED is inside of a aluminum block to help dissipate heat. Do you think and LED like this...
  32. X

    Second-order coherence – g2(t) of collision-broadened light and LEDs

    Hi. I have 2 questions about second-order coherence – g2(t): 1) For collision-broadened light according to the literature g2(t)=1+|g1(t)|^2, where g1(t) is the 1st order coherence. Therefore for very low collision rate g1(t) =1 and thus g2(t)=2. However I would expect collision broadened...
  33. N

    Waveguiding, Modes, Organic LEDs

    Hi everyone, I was wondering if someone could please explain to me the concept of waveguiding, coupling/coupled, and guiding mode. Here is an application of these terms: The photons emitted in the active region of OLEDs are coupled into three types of modes: direct transmission into...
  34. M

    RGB LEDs in series - turn Green on

    Hello, I have a high power RGB LED with common anode. I want to have 3 of them in series, and put them on 15V power supply. And I want to switch green color on, and red color as well (something like a normal traffic light) Here is the problem: Given that three LEDs are in series, and are...
  35. K

    Is it possible to control LED lights with a DVD player output?

    Hello, I am working on a sound/light installation at the moment and was hoping that someone on here might be able to help me with a question i have. I would like to use the composite output from a DVD player to control the intensity and hue of LED light (or 3 (RGB) if need be). So...
  36. D

    Connecting LEDs with Resistors: Step-by-Step Guide

    hi everyone, I am new to this forum, hope I am posting a thread in the right place, if not could any MOD please place my thread correctly... thanx guys i need to know how to connect my resistor to a LED i have 12 white leds 5mm that is 3.6v each @ 30mA im using a 12V power supply for...
  37. N

    Using transistor to switch leds on/off

    I'm currently using this circuit, but without the rectifying portion,a audio source from mp3 player instead of a mic, and a 4V LED instead of a bulb. My power source is 12v. However, the voltage across the LED is only around 1-1.5V. How can i increase the voltage across the LED? Here is what i...
  38. N

    Superbright leds and potential dividers

    I'm trying to feed a voltage to my superbright leds. I am not sure how many voltages they require to work(6v?) I have a 12V dc supply from my computer's power supply unit, which i connect to the potentialmeter(500K, 1M). I then tap the voltage and pass it directly to my LED. However, when I...
  39. G

    Conventional square and triangular LEDs

    Could someone please differentiate this to me? "Why Conventional square LEDs are less efficient than triangular LEDs. If any of you guys could help me out, or point me in the right direction, it would be a great help! Thank you in advance!
  40. K

    What do I need to run 200 LEDs on 110V

    I want to build my own under cabinet LED strips for my kitchen. I am looking at wiring 200 Nichia T1 3/4 LEDs to one AC circuit. But I am having problems finding any directions to build the circuit or driver to power a system like this. If I need to buy a premade step down transformer then I...
  41. madmike159

    Why do blue LEDs have a higher forward voltage than expected?

    My physics/electronics teacher told me some thing really interesting and confusing a wile ago and I have been trying to get my head round it. The forward voltage in a LED (voltage needed to drive the current) is proportional to the band gap energy. However Blue LEDs have a higher forward...
  42. B

    Calculating Resistor Value for Driving LEDs with an NPN Transistor

    Homework Statement an npn transistor is used to drive a constant current I through three ‘white’ LEDs, connected in series. If the required current value is I = 25 mA, and the current-gain of the transistor is β = 300, find the value of the resistor R, giving your answer to 3 significant...
  43. P

    Need power supply for 200 5 volt leds

    I'm thinking of making a 200 led grow light using red and blue leds(5v). I have little knowlage on electronics. I was wonder if a computer power supply could be used and what other componets would be needed. I'm trying to get this built by late February to start growing my veggies (new project...
  44. L

    Why LEDs Have a Broadened Spectra?

    Why is it that LEDs do not sharper spectra? I've been considering this recently, and was wondering if it was due to the uncertainty principle (like homogeneous broadening in a laser) or is it due to a fluctuating band gap? I've searched high and low and can't find any explanation for the...
  45. D

    What kind of battery do I need for my LED motorcycle lights?

    first of all HELLO evry1,i am new here! I have a motorcycle and I want to do something special to it so I decided on putting some LEDs on. I buyed 20 pre-wired LEDs...
  46. H

    Control LEDs with Audio: A/D Converter & Microprocessor

    I am trying to control a bunch of LEDs to respond to different audio frequencies. I have a microprocessor with A/D converter and know how to use these, but I have no idea how to go about the rest of it. Thanks in advance!
  47. P

    Connecting 6 * 3mm/5mm LEDs with 3V Supply

    Hey guys, I have a question regarding connecting up 6 * 3mm/5mm super bright mcd Led's in parallel (since they would all have the same forward voltage when wired this way), using a supply voltage of 3V but not sure whether is should be 2*1.5V AAA or 2 * 1.5V AA batteries. The reason i put...
  48. R

    Newbie wiring 20 red LEDs to a 9v battery in parallel help pls

    Newbie wiring 20 red LEDs to a 9v battery in parallel...help pls :) hello, i am completely new to the LED world and electronics world. I am wanting to make a little box with LED lights as an aniversary gift. Basically what I need to know is how to wire 20 red LEDs in parallel so that they...
  49. ZapperZ

    UV LEDs could be a reality soon

    http://physicsweb.org/articles/news/10/5/10/1 Zz.
  50. W

    Toronto Doctor takes pictures of small intestine with LEDs and camera in a pill

    http://www.cbc.ca/stories/2002/09/04/video_pill020904 sorry if it's not new news , but i just saw it on tv and thought it was very cool..
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