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. Borek

    What is the SMD challenge misery edition?

    @berkeman - remember the guy who asked about replacing 0603? Quite accidentally I just found something called "SMD challenge misery edition" (there are several versions, TBH I have no idea which one was first so I just grabbed the best picture I could find). Yes, the idea is to hand solder the...
  2. Solid-Statist

    High-Power LEDs -- Maximum 'Lumen-Density'?

    Light-emitting diodes (LEDs) are replacing traditional lighting technology -- such as halogen -- in high-power lamps, as LEDs are much more efficient (Lumens/W) and longer-lasting. A commercial example of high-power LED flood lights: High Power 3000W LED Flood Light - Lsleds NOTE: The above...
  3. NTL2009

    LED/"LASER" Printers - How are +5000 LEDs addressed/controlled?

    I recently re-watched this video: And I wondered, how are +5000 LEDs addressed/controlled? At 600 x600 DPI and an 8.5"x11" printing area, you need ~ 5120 LEDs across and 6600 scans. At 20 ppm, the scans would need to be less than 3 seconds total ( need to allow time for fusing, etc), so ~...
  4. O

    Connect: Coupling Light from 2 LEDs into a Single Fiber

    Hi, I am looking for a suitable method to couple light from 2 LEDs into a fiber and then join both fibers, so that I only have one fiber at the end so that both wavelengths can be emitted from a single fiber. The first coupling step from LED into fiber seems to be more easy, I already heard...
  5. J

    Understanding the effect of duty cycle on the brightness of LEDs

    The brightness of an LED is a result of the current passing through it. The current is a function of the voltage across the LED. The duty cycle represents the percentage of the time period that the signal is in the ON state ( which means that the voltage is at max value as compared to 0 V for...
  6. WonderfulWorld

    Calculating the Efficiency, total output power and irradiance of LEDs

    Hi Everyone, This is my first post and I hope to work with you on this to gain a fuller understanding. I'm currently designing an LED circuit with 60 3 watt LEDs. Input power is both 120VAC for North American and 230VAC for other countries. I know this is pretty basicbut what is the best way...
  7. fluidistic

    Hardware recommendation to control LEDs individually

    My two years old son loves lights and computers. I was thinking to buy an Arduino or a Raspberry pi like single board to control a LED matrix panel. What I want is to be able to control individual LEDs by pressing on keys on a keyboard. Example: by pressing "a", a LED lights up, "b" another LED...
  8. kolleamm

    Controlling 100 LEDs with a PC?

    I would like to turn on and off 100 external (non screen) LEDs through my PC. I was thinking to assign each pin on my serial port an LED, because apparently you can control the power on serial port pins if I understand correctly. The problem is that even if I do control each pin on a port, what...
  9. D

    Creating Coherent Light from UV LEDs and Pinhole Aperture

    I've read that using a pinhole aperture and a wavelength filter can turn a "white" incoherent light source like a light bulb into a temporally and spatially coherent light source (albeit at low efficiency). Can a temporally and spatially coherent light source be made with a monoenergetic (or...
  10. C

    Bypassing a joule thief until voltage gets low enough

    I'm working on a small crank-able light using a DC motor,capacitors, and LEDs with a joule thief to drain the capacitors completely when the voltage in them drops too low for the LEDs. However I want the power from the capacitors to be able to go directly to the LEDs before the capacitors drop...
  11. sophiecentaur

    Reliability of LEDs: PF Members' Views and Experience

    Yet again, I am getting furious about the reliability of domestic LEDs. I have been moved to ask for the current views and experience of PF about them. The top of my search list on PF has an old 2012 post of mine, moaning about the same thing. There are some interesting comments from PF on that...
  12. N

    LEDs in parallel don't consume the sum of individual currents?

    Hello all. Thanks for taking up your time to read my post. I checked the currents that passed through several LEDs for MIC2287CBD5 as the datasheet of http://www.kynix.com/uploadfiles/pdf2286/MIC2287CBD5.pdf at a particular voltage. They varied from 12.0 to 15.1 mA at 3.0 V. I then connected...
  13. L

    Simple and clear LED question. LEDs pop and break

    Attached is a picture of my set-up. It is very simple and if for a car (12V) The LED kit comes with 3 options: Hard wire install, cigarette lighter install, and 9 + 9 V battery demo. The peculiar thing is when I connect the hard wire install plug (shown at the top of the picture) to a...
  14. B

    HOW TO: Stop efficient LEDs from lighting up when off

    Saw an old thread, "Led Lights Burn With Power Off" and it was closed... so let me check out an issue with you all: in this same situation and I don't want the lights softly glowing, could I put a 100 ohm 1/4 watt resister in line to block the teeny tiny induced current? Would it behave well...
  15. G

    Drive 4 LEDs at 20mA with 12V Battery: Resistor Value?

    Hi all, a bit of a hypothetical for you. If I wish to drive a 3V LED at 20 mA from a 12V battery, I can use a dropper resistor. I subtract the LED's forward voltage from the 12V to get 9V, and divide this by the 20 mA, to get the value of resistor needed. R=V/I = 9/0.02 = 450 ohm. However...
  16. A

    Backing-out luminosity togo from lumens to radiant flux in W

    Hi. Has anyone already done the work to back out the standard luminosity function so I can go from lumens at a particular wavelength to radiant flux in Watts? I have visible LED spec sheets with optical characteristics in lumens and I want to calculate the outputs in W. My NIR LED has specs in...
  17. Borek

    Why do LEDs in a circuit need resistors in series?

    I am playing with Arduino and LEDs at the moment. LED needs a resistor to limit current, that's clear. However, all examples I see use separate resistor for each diode. As far as I can tell electrically (in terms of limiting current) it shouldn't matter much whether we use single resistor for...
  18. Metals

    I Blue lights (LEDs) consume more power than red (and green)?

    Referring to LEDs as I'm not aware of any other "colour-producing" light, does blue light use more energy than red light? Planck's formula (E=hf) leads me to believe that blue light would drain a battery quicker than red, due to its higher frequency. Surely a device emitting blue light would...
  19. F

    Question about LEDs relative to voltage

    Back story : I have cheap 12v LED 5050 strip from China. Question: how do LEDs respond to 13v and 14v in terms of % intensity with higher voltage neglecting lifespan and assuming proper heat dissipation. Details: the LEDs at 60/m rated 14.6w at 12v. They are typically 3led in series with a...
  20. Anton Alice

    Detecting fluorescence via CW or pulsed LEDs

    Hello forums, in the context of a little DIY-project I am planning to build a rudimentary fluorometer, which is actually doing nothing but checking whether an amount of protein is fluorescing or not, and roughly measuring its intensity. A highpower LED is used to excite the protein to the...
  21. SmritiB

    Detecting Current Flow in a Circuit with LEDs

    I am desgning a circuit(network), where i need to show the path traversed by the greater part of the current at each node, consecutively. using an ammeter (or voltmeter) in every branch (around 20) makes it too tedious. Will LEDs do the required work? But they would light up at all locations...
  22. J

    Can LED bulbs be safely used in motorcycles without additional modifications?

    I have a small motorcycle and have changed the incandescent bulbs to LED. It seems the bulbs were powered by AC off the magneto generator and AC thru the rectifier powered the 6 volt battery. Is it ok to run LED this way or should I add diodes like in option a or b of diagram?
  23. R

    Design of a short circuit kit for DUTs (switch, opamp, LEDs)

    Hi folks, I would like to clarify few doubts on my mini-project as mentioned below: I am designing a small kit using a transistor (2N3904) and an OP-AMP (LM741- Voltage follower) with few resistors connected to them. My power supply voltage value is 5V. Please refer to the below picture for...
  24. J

    How many LEDs from fixed supply

    How many led's 20ma at 3 volt can one run from a fixed supply voltage of 110 volt dc and a maximum supply of 20ma? I come up with 36.
  25. E

    LEDs, LED Drivers, Thermal Management

    I'm trying to wrap my head around thermal management of LEDs and LED driver circuits. http://blogs.indium.com/blog/amanda-hartnett/controlling-junction-temperature-of-leds-with-thermal-management-materials A concern has been expressed that a lighting supplier needs to demonstrate (not sure...
  26. J

    What to optimize in LED array?

    I'm making an array of 11 3.3V LEDs, and I've got multiple various setups possible depending on source voltage (batteries supplying either 6V, 9V, or 12V) and whether I decide to put a bunch of the LEDs in a combination of series/parallel or all in parallel. I need to maximize battery life, so...
  27. I

    What's the color temperature for LEDs indicate?

    Specifically what does the color temperature on light bulbs it indicate? because, it clearly does not indicate the wavelength of max intensity.
  28. L

    What is the biggest challenge to improve white LEDs?

    Here are some of my thoughts: - thermal management of individual LEDs in a RBG system - photon absorption in phosphor coating - exponential decay in intensity - CCT/ CRT?
  29. J

    Maximizing Efficiency: Using Luxeon S LEDs for Solar Simulator Design

    I want to make a solar simulator with LEDs. I want to get a net intensity of 1 Sun(1000 W/m^2). My LEDs have the following specifications: LUXEON S LXS8-PW30 Luminous flux at 700 mA, 85°C* 1315 lm Radiant flux at 700 mA, 85°C 4113 mW 1931 CIE color points at 700 mA, 85°C (0.4304, 0.4030)...
  30. J

    Why do LEDs continue to emit light?

    The electrons need energy to cross the potential barrier between the N and P types. So apply a voltage and they get over and recombine with the "holes" and emit a certain wavelength of light. Then what happens? Does the voltage have to be great enough to then knock them out of the holes and send...
  31. Celestion

    Optimum mounting angle for three LEDs in a 240V LED light bulb

    Homework Statement The asker needs to know the angles to mount three LEDs inside a traditional mains powered light bulb shaped enclosure "to get even radiation from the LEDs", and also the position of the covering plastic sphere in relation to the LEDs. (I was thinking that the position of the...
  32. rogerk8

    What makes 0603 LEDs stick to probe?

    Hi! I had an interesting chat with a physisist colleague of mine this week. Working with modern small electronic components I began to wonder why my extremely pointy probes, measureing the direction of the light emission diode, stuck so irritating hard to it that it could not break loose after...
  33. I

    How Do LEDs Age? Shopping for LED Bulbs & Est. Lifetimes

    i'm shopping online for an LED bulb and one site gives the estimated lifetime of the LED. So, i was wondering what exactly is happening to make the device "old" and no longer work?
  34. E

    Tiny LEDs: What to Do With Them?

    Hi All, The other day I ordered LED's from digikey to do some electrical experiments for fun, and to my surprise I got these: http://www.digikey.com/product-detail/en/SMLP12WBC7W1/511-1616-2-ND/1801991 They are literally too small to even hold. They are like the size of knat. What do I do...
  35. V

    Knock sensor and progressive Leds

    I am detecting detonation in a SI engine using a knock sensor (pizeo element). What I would really like is to have 3 leds that light up as the knock gets more severe. I have the knock sensor running into an op amp powered by a 9v battery. I am listening to the output with a pair of head...
  36. S

    Using RF Transmitter/Receiver to power LEDs from a Sensor?

    I have a pressure sensor that gives off 4 volts when actuated and I would like to transmit it a distance to an LED light. So I found these RF Link Transmitter/Receiver at 434MHz: https://www.sparkfun.com/products/10534 https://www.sparkfun.com/products/10532 The data sheets and...
  37. S

    Calculate optical power output of LEDs

    Hi guys, I have to calculate de optical power output of a set of LEDs. For that I used a photodiode to measure the photocurrent at each wavelength and then calculate the optical power at each wavelength using the following formula: R (A/W) = I/P, where R is the responsivity of the...
  38. R

    Help creating a series of 2 LEDs

    Hi, electrical engineering has always interested me and recently I have been trying to trying pick it up as a hobby by doing simple soldering exercises. While everything has gone smooth so far, I have hit a snag with the current little project I have been working on. So my goal is to light 2...
  39. O

    LEDs not as awesome as presumed

    I bought some 'super bright' LEDs from sparkfun: https://www.sparkfun.com/products/8861 I got the green one, the red one, and the blue one. Guys in the comments are saying, "Wow these things light up a whole room at 75mA!" So I bought them to make a night light. I checked out the...
  40. M

    How to wire LEDs through magnets?

    Hi guys. I'm an architecture student who is designing a lamp that will be made up of multiple, modular pieces of plywood. Each piece will be a hexagon containing 6 LED lights (one on each side). The idea is to have a base that plugs into a socket with a wall wart: I was thinking 12 volts AC...
  41. S

    Need help upscaling this circuit for leds.

    Hello everyone, I am currently a sophomore in computer engineering, so I don't quite know enough to figure this out on my own, so I was hoping you guys could help me. I really like the idea of a color organ to visualize music...
  42. J

    Current Mirrors to drive LEDs.

    Hi all, I am trying to build a circuit for driving multiple LEDs under test at a given current, and the LEDs are to be individually tested with multimeter. Now I know I could just run them all in series and they would get the same current, but if one LED breaks, then the whole circuit goes...
  43. D

    Powering small LEDs over Cat5?

    Ok so I've been trying to power a few small lights in my shed and I've read on a few sites about PoE (power over ethernet). i just wondered or has anyone had experience with it? what kind of current/voltage is the cable capable of etc I am guessing its not just as simple of wiring 2 of the 8...
  44. S

    Engineering How to make a Logic Circuit with 5 LEDs and a 3V battery? Nothing else allow

    Homework Statement We can't use anything else, and just have to make a logic circuit (either OR, AND or NOT) with just this material. We can use less or more diodes but I have only 5. Homework Equations The Attempt at a Solution I tried setting it up like doides but no help at...
  45. R

    How do I test for UV light in colored LEDs?

    I recently purchased two strings of RGB LED lights, the kind you can set to all sorts of colors by combining red, green and blue in various amounts. Unfortunately, I strongly suspect that the blue and green led-pieces produce light that is contaminated with UV. Various UV-reactive things in...
  46. M

    About LEDs technical question - very hard to solve

    In a COB product with FR-4 substrate, blue light chip excites yellow phosphor to form white light. Why is room temperature aging attenuation higher than 85 degree/85% RH aging attenuation? (After 1000h lighting, Attr=7% while Att85=1%) (If you have further questions about how I do the...
  47. B

    Installing LEDs in footwells, will a diode work?

    I’m trying to install some LEDs in my footwells. I have a pink wire, which is my positive, and a gray wire, which is my negavtive. This is a negative switched circuit. So, is it ok to hook it up like this? 1 Positive of LEDs to pink, negative to gray. 2 Then, use a diode on the gray...
  48. Freddythunder

    Best practices using 555/4017 & many LEDs

    Hello, I'm new here.. I have a question about running a lot of LEDs in a couple scenarios. I'm building a full-size lightbar for a fake police car to be used in movies. I found a schematic for the red & blue LEDs that I'm going to duplicate using some 555s or 556 here...
  49. G

    Some noob questions on wiring LEDs, current, etc.

    I'm making a wearable project that involves me wiring up about 16 LEDs into a piece of clothing. Unfortunately, it's been many a year since I took a physics course and I'm a little rusty on things. Here's my situation: The LEDs drop about 2V each, and are meant to be used with a current of...
  50. I

    Light transmitting material with LEDs: Advice needed

    Hi, this is my first post here on the forum although I've been following some other threads recently. I'm currently working on a thesis project with a colleague of mine in which we are engineering a night time pacifier. We are at the moment trying to find a way to make the shield of the...