Questions tagged [led]

An LED is a light-emitting diode. Lighting an LED is considered the "Hello world" of a circuit design, and it can be as simple as using a series resistor, or it can get more complicated, involving PWM and multiplexing.

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Usage

An LED is the most common opto-electronic device, which generates light from the electron-hole recombination mechanism in the P-N junction.

LEDs have long been used as indicator lights, but in recent years high-power LEDs are being used as incandescent lamp replacements.

Theory of operation

The color is determined by the energy gap between conduction and valence band of the semiconductor used, which determines the energy that the photon generated by the recombination mechanism has.

Being a diode, it's characterized by a threshold voltage (of about 1.8 to 5 V depending on the color), below which the current is nearly zero, and beyond which the current increases exponentially. In a first approximation, the voltage is considered almost constant and equal to the threshold.

Most LEDs require current limiting, for which a series resistor can be used.

Schematic Symbol

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Notes

  • For questions about a specific part, please link to the datasheet.

Further reading:

Don Klipstein's LED Main Page

Frequently asked LED questions:

Correct formula for LED current-limiting resistor?

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How can I efficiently drive an LED?

I understand that I can not connect an LED directly to a battery because it will draw too much current. Thus, there must be something else in the circuit to limit the current. What options are there? Are some methods more efficient than others?
Phil Frost
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Why exactly can't a single resistor be used for many parallel LEDs?

Why can't you use a single resistor for a number of LEDs in parallel instead of one each?
Dataflashsabot
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Why does a resistor need to be on the anode of an LED?

Please be kind, I am an electronics nub. This is in reference to getting an LED to emit photons. From what I read (Getting Started in Electronics - Forrest Mims III and Make: Electronics) electrons flow from the more negative side to the more…
Spechal
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What is "forward" and "reverse" voltage when working with diodes?

What is the difference between "forward" and "reverse" voltages when working with diodes and LEDs? I realize this question is answered elsewhere on the interwebs such as wikipedia, but I am looking for a short summary that is less of a technical…
JYelton
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Why did LEDs take so long to appear as light bulbs?

LEDs are an old technology, why did the industries take so long to put them into light bulbs? Was there any technological gap missing?
PDuarte
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Why is kerosene stopping my red LEDs from illuminating?

I initially posted this on chemistry.stackexchange but didn't get any answers, so I'm reposting it here. Long story short - we have an electronic product that is submerged in fuels (kerosene being one of them) and uses an RGB LED (click here for…
Amr Bekhit
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What is the latency of an LED?

LEDs are known to have a very low, unnoticeable power-cycling latency, but how fast are they when measured? (nanoseconds?) In other words, how long does it take for an LED which is entirely off to get to its optimum brightness, and how long does it…
ayane_m
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Why would one drive LEDs with a common emitter?

I've seen tutorials aimed at beginners suggest the way to drive an LED from something without enough current drive is this: (option A) but why not this: (option B) Option B seems to have some advantages over option A: fewer components the…
Phil Frost
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Are LEDs better than we think?

Conventional wisdom about LEDs says their maximum reverse voltage \$V_{R(max)}\$ is quite limited, usually in the 5V-8V range. So, for experimentation purposes, I wanted to bring an LED into controlled breakdown, using my current-limited power…
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What is the purpose of tiny "bumps" on LED legs?

A lot (if not most) LEDs have some kind of small thickenings on their legs. Sometimes they are almost as wide as the leg itself and barely visible, sometimes they are twice as wide and instantly noticeable. When present they seem to be the same on…
HYBRID BEING
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Do I really need resistors when controlling LEDs with Arduino?

I'm just trying out Arduino Uno for the first time with 2 blinking LEDs on a breadboard. All the tutorials on the Internet seem to use a resistor. I do know the function of resistors, but does it really matter here? These LEDs are working just fine…
40pro
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Does pulsing an LED at higher current yield greater apparent brightness?

This question implies two assumptions: The frequency of a switched LED driver is high enough that average power, not instantaneous power, should be used to determine maximum drive current. The limiting factor which determines maximum current at…
Kevin Vermeer
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Is a current-limiting resistor required for LEDs if the forward voltage and supply voltage are equal?

For blue LEDs with a forward voltage of 3.3 V and supply voltage of 3.3 V, is a series resistor still needed to limit current? Ohm's Law in this case says 0 Ω, but is this correct in practice? Perhaps just a small value like 1 or 10 Ω just to be…
Craig
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Why hasn't my LED burned out by now?

I have a 15 year old ReplayTV DVR. I got it used, I'm not sure when, but probably about a decade ago. It's turned on almost all the time, and it has a blue power LED on the front. The LED FAQ says that many LEDs have a rated lifetime of 50,000…
Barmar
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Easy way to figure out a LED's Vf in order to pick an appropriate resistor

I was wondering what the easiest way to figure out a LED's forward voltage is, using measurement tools. I know we can assume red LEDs to be around 1.8V - 2.2V, and that we have similar information for other LED colors, but I was wondering if…
diegoreymendez
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