Picture of All You Need to Know About LEDs
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An Light Emitting Diode is an electronic device that emits light when current is passed through it. LEDs are small, extremely efficient, bright, cheap, electronic components. People think that LEDs are just common light emitting components & tend to overlook the Interesting Facts & Features of LEDs. In this instructable I will teach you ‘All You Need to Know About LEDs’ which includes their Working, Voltage, Current and Power Ratings, Builds, Types, Resistor Calculator for LEDs, Uses, Testing & a Simple LED circuit.

Here’s a Link to the ‘LED Resistor Calculator’ free android app: LED Resistor Calculator . This app helps you calculate the appropriate resistor value required for an LED.

History Of The LED

Oleg Vladimirovich Losev observed light emission from carborundum point-contact junctions, the first light-emitting diode (LED). In course of his work as a radio technician, he noticed that crystal diodes used in radio receivers emitted light when current was passed through them. In 1927, Losev published details in a Russian journal of one of the first light-emitting diodes. A couple of years later Nick Holonyak, Jr. invented the first visible-spectrum (red) LED in 1962 while working as a consulting scientist at a General Electric Company laboratory in Syracuse, New York.

  Step 1: Composition & Working
Picture of Composition & Working
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  1. Dremeling an LED.
  2. Top view of the Electodes of the LED. (larger- cathode, smaller- anode).
  3. Closeup of Anode and Cathode of LED. (LED sliced in half).
  4. Anode and Cathode of LED removed from plastic shell.


An LED is an electronic component made up the following elements: Gallium (Ga), Arsenic (As), and Phosphorus(P). These elements are Semiconductors which are also used in various other Electronic components.


A LED is a P-N Junction diode that emits Light. When an LED is in forward bias it emits light instead of heat generated by a normal diode. When the P-N junction is in forward bias, in case of a LED some of the holes combine with the electrons of N- Region and some of the electrons from N combine with hole from the P- region. Each recombination radiates light or Photons.

LED’s do have a polarity and hence do not work if they are connected in Reverse bias. The easiest method to check the polarity is by holding the LED close to your eye. You will see that there are two electrodes. The thicker one is the Cathode(-). Light is emitted from the Cathode. The thinner electrode is the Anode(+). Generally LED’s are manufactured so that the lenght of the leads of the Cathode and Anode differ. Due to this LED’s are manufactured with the Anode(+) lead longer than the Cathode(-) lead. This also makes it easier to determine the polarity.Note: Some manufacturers do keep both electrode leads the same length. Inorder to TEST the polarity you will need to use a Multimeter.

Step 2: Volatge, Current & Power Ratings

Picture of Volatge, Current & Power Ratings

IMAGE: LED Symbol.

Voltage Ratings

LED’s generally have a standard voltage rating. Most LED’s require about 1-2 Volts. The voltage required by an LED sometimes depends on the Colour of the LED. If you supply excess voltage the LED will burn and get damaged. On the other hand if you supply very low voltage, the potential difference required to carry the current will be insufficient.

Current Ratings

Current ratings of LED’s are similar too Voltage Ratings. LED’s generally have a standard current rating. Most LED’s require about 5-25 mA. The current required by an LED sometimes depends on the Colour of the LED. If you supply excess current the LED will burn and get damaged. On the other hand if you supply very low current the LED will not produce its maximum output.

Power Ratings

An LED’s can have various power ratings depending upon their Type, Build and Voltage/ Current Ratings, etc. LED’s also come in ‘High Power LED’ packages. LED’s are way more effecient than conventional light bulbs such as CFL’s and Incandescent Bulbs. When comparing an LED as a light fixture it consumes 6-8 Watts less than that of an Incandescent Bulb (60 Watts) or a CFL (13-15 Watts). Hence LED’s are extremely efficient.

Step 3: Build

Picture of Build
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  1. Basic LED.
  2. Dome LED.
  3. SMD LED (Large).
  4. SMD LED (Small).
  5. Display LED used in 7-Segment Display.

LEDs are produced in a variety of shapes and sizes. The color of the plastic lens is often the same as the actual color of light emitted, but not always. For instance, purple plastic is often used for infrared LEDs, and most blue devices have colorless housings. Modern high power LEDs such as those used for lighting and backlighting are generally found in surface-mount devices (SMD) packages. Some LED’s have diffused plastic lenses.

Basic LED

The basic LED is one of the most widely used LED’s. Due too it’s popularity its pice is relatively cheaper compared to othe LED’s. It looks very basic and the design is very simple.

Dome LED

This is a type of LED which is shaped liked a ‘Dome’. This shape is designed too increase the area to which the light is transmitted. In other words the Angle of Emission( Circumfernce) of Light from the LED is greater than the Basic LED. Although this type of LED is slightly more expensive than a basic led.


This type of LED is generally very small in size. SMD means Surface Mounted Device. And as its name suggests, this LED is soldered onto the surface of the PCB unlike conventional ‘through- hole’ components. These LED’s are Generally soldered by Machines( Precise Soldering Robots) and are extremely difficult to solder by hand (Although it isnt impossible to Solder SMD LED’s by Hand).

Display LED

This type of LED is mainly used in displays as its shape is flat.

Step 4: Types

Picture of Types
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  1. Dome LED’s.
  2. IR LED’s.
  3. 7 Segment Display LED
  4. Tri colour LED (colour changing LED).

Colour LED

Coloured & White LED’s are mainly used in Indicators, Lamps, Lighting Equipment, etc. They are one of the most commonly used LED’s

Colour Changing LED (Tri/Bi Colour LED)

In this type of LED, the colour emitted by the LED changes within a specific period of time. A tiny Integreated Circuit (IC) is embedded into this LED inorder to control the time delay between transitioning the various colours.

Infrared (IR) LED

This type of LED beams infrared rays of light. These infrared rays cannot be seen by the Human Eye. This type of LED generally works on a transmission frequency of 38KHz. Its mainly used in Remote Controlled and Small Range Communication devices. You can test a IR LED by viewing it under a Camera whilst a current is appliead across the LED. In other words cameras can detect IR rays emitted from the LED.

7 Segment Display LED

A 7 segment display LED is an LED consisting of 7 display LED’s connected in the form of an 8. Its used in calculators, displays, etc. An LED similar to this is also used to display alphabets.


UV LED’s emit Ultra Violet rays of light. These rays have various applications such as Sterilization, Water purification, etc.

Step 5: Resistor Calculator for LED’s

Picture of Resistor Calculator for LED's
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  1. Various resistors and a LED.
  2. LED Resistance Calculator App Logo.

So the most common question asked about LED’s is the appropriate resistor to use along with. The reason a resistor is used along with LED’s is to protect them from excess current which can burn and damage the LED. But choosing the right LED isn’t that simple. Why? Well if you choose a very high resistance, the LED will not emit its maximum light. And if you a low resistance there are chances of the LED getting Damaged.

So a simple formula was invented:

Resistance = (Source Voltage – LED Voltage) / (LED Current / 1000).

Inorder to make this calculation easier you can use this free Android App LED Resistance Calculator. It is an app designed especially for this Instructable. Other features and more electronics related functions and calculators will be added to this app. The app was developed by Nathan Neal Technologies. He also undertakes various other projects in developing Apps, Websites, Computer Programs, etc. You can contact him through his website.

Step 6: Uses

Picture of Uses
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  1. TV Remote without button pressed.
  2. TV remote with button pressed and IR LED flash detected.
  3. Strip of Dome LED’s from an Emergency Flashlight.
  4. LED Flash of a Smartphone Camera.
  5. LED power indicators of a Laptop.

LED’s are used everywhere. From your phone flash, to your cars music system, to your garden lights, to your TV display. Basically their adaptive nature and effeciency has given them a place in most electronic gadgets.

Some of the most known uses are:

  1. Lighting.
  2. Displays.
  3. Indicators.
  4. Decorative Lights and Objects.
  5. Remote Control.
  6. Sterilization.
  7. Purification of Water.
  8. Dentistry & other Medical applications.

Step 7: Testing & Circuit

Picture of Testing & Circuit


  1. Multimeter used to test LED.
  2. Simple circuit using LED.


An LED can be tested inorder to check whether it is working properly using a multimeter & by following the steps:

  1. Set the dial of the multimeter to the ‘Continiuity’ function.
  2. Now connect the Anode(+) of the LED to the RED/Positive/(+) probe of the multimeter & connect the Cathode(-) of the LED to the BLACK/Negative/(-) probe of the multimeter.
  3. If the LED is working the Multimeter will start to make a ‘Beep’ sound. And a value will display on the screen of the multimeter. In addition to this the LED should light up.
  4. You can also Test the LED and any other component with the help of this circuit:- Electronic Sensor Component Tester


This is one of the most basic and versatile circuit you can find which uses an LED in it. The reason it is a great circuit to start of with is that it can also check the working of any other Electronic components or Electronic Sensors. You can also check out a detailed tutorial which will help you to make this circuit: Electronic Sensor Component Tester