A light-emitting diode (LED) is a semiconductor device that emits visible light when an electric current is passed through it. LEDs are used in various applications, including indicator lights on electronic devices, traffic signals, and illuminated signs. In this article, we will discuss the working, characteristics, and applications of LED.
Symbol of LED
The symbol of LED is shown in the figure below. Two arrows (projecting outward) represent the emission of light. LED has similar electrical characteristics to a PN junction diode. It allows current to pass during forward biasing and blocks current in reverse bias.
Note: The leg of the anode is longer than the cathode.
How does an LED emit the light?
LEDs emit light when current flows through them. The figure below shows a simple circuit in which an LED is connected to a battery with a resistor. When the switch turns on, the LED conducts current and starts glowing. Let us understand the process in detail.
When electrons recombine with holes within the semiconductor material, they release energy in the form of photons. The photons emitted by the LED are then funneled out through a lens, which focuses the light into a beam.
When the diode is forward biased, minority charge carriers(electrons) move from p-type material to n-type material. Similarly, minority charge carriers(holes) move from n-type material to p-type material. At the junction, the extra minority carriers recombine with the majority charge carriers. Thus energy is emitted in the form of photons.
In ordinary diodes, energy is released in the form of heat during recombination. But in LEDs energy is emitted in the form of photons.
Must read: A Beginner’s Guide to Diode (Definition, symbol & working)
Why a series resistance is required in this circuit?
An LED might get damaged when a forward voltage is directly applied to it. The LED will draw all the permitted current from the supply and may get damaged. To limit the current, a series resistance is connected with the LED.
How much current does an LED draw?
An LED typically draws current in the range of 10-30mA. The current flow determines the brightness of the LED, and the higher the current, the brighter the LED will be. However, too much current can damage the LED, so it is important to find the right balance.
What is Electroluminescence?
Electroluminescence is the phenomenon of a material emitting light in response to an electric current. When an electric field is applied to these materials, it causes electrons to flow from the positive electrode to the negative electrode. As these electrons move through the material, they collide with atoms and release photons (light particles). The frequency of these photons determines the color of the light that is emitted.
How different colours are produced by LEDs?
The color of the light that is emitted by an LED depends on the material that is used to create the semiconductor. For example, red LEDs are typically made from materials like gallium arsenide, while blue and green LEDs are typically made from materials like indium gallium nitride.
By changing the material used to create the semiconductor, manufacturers can produce LEDs that emit a wide range of colors. The table given below shows the emitted colors of LED and their corresponding wavelength, voltage drop, and materials used for manufacturing that particular LED.
| Colour | Wavelength (nm) | Voltage Drop (V) | Semiconductor Material |
| Infrared | > 760 | < 1.9 | Gallium Arsenide, Aluminium Gallium Arsenide |
| Red | 610 – 760 | 1.6-2.0 | Aluminium Gallium Arsenide, Gallium Arsenide Phosphide, Aluminium Gallium Indium Phosphide, Gallium Phosphide |
| Orange | 590 – 610 | 2.0-2.1 | Gallium Arsenide Phosphide, Aluminium Gallium Indium Phosphide, Gallium Phosphide |
| Yellow | 570 – 590 | 2.1-2.2 | Gallium Arsenide Phosphide, Aluminium Gallium Indium Phosphide, Gallium Phosphide |
| Green | 500 – 570 | 1.9-4.0 | Gallium Indium Phosphide, Aluminium Gallium Indium Phosphide, Aluminium Gallium Phosphide, Indium Gallium Nitride |
| Blue | 450 – 500 | 2.5-3.7 | Zinc Selenide, Indium Gallium Nitride, Silicon Carbide, Silicon |
| Violet | 400 – 450 | 2.8-4.0 | Indium gallium Nitride |
| Purple | multiple types | 2.4-3.7 | Dual Blue/Red LEDs, Blue with Red Phosphor, White with Purple Plastic |
| Ultraviolet | < 400 | 3.1-4.4 | Diamond, Boron Nitride, Aluminum Nitride, Aluminium Gallium Nitride, Aluminum gallium Indium Nitride |
| Pink | multiple types | 3.3 | Blue with phosphor, Yellow with Red, Orange, or Pink phosphor, White with Pink pigment |
| White | Broad spectrum | 3.5 | Blue/UV diode with Yellow Phosphor |
Types of LED
There are different types of LEDs manufactured using semiconductors.
RGB LEDs
RGB LEDs stands for Red, Green and Blue LEDs. Three LEDs in a single case. We know red, green, and blue are primary colors and their combination can produce different colors. By controlling the intensity of each light we can produce various colors. It has 4 legs. One common pin acts as an anode and the other three are for illuminating three colors.
Addressable LEDs
These LEDs can be controlled using a chipset. WS2812, APA102, UCS1903, etc are some of the chipsets.
Built-in Resistor LEDs
These LEDs have a chip to control limiting currents.
Read also: 10 Different Types of Diode – Symbol, Uses & Features Explained
High-Power LEDs
They are superpower LEDs. They dissipate 1 watt (or more) of power. They generate heat and might damage if no proper cooling method is used with them. So a heat sink must be attached to them.
Bi and Tri-Colour
It will contain two or three colors encapsulated in the same case to produce a variety of colors. It has two or three terminals.
Alphanumeric LED
They are used to display characters and numerals.
Lighting LED
LEDs are used for decorations, interiors, walls, etc.
Advantages of LED
- Low power consumption
- Long life (35,000 to 50,000 hours of useful life)
- Low operating voltage
- Available in a wide range of colors
- Compact size and can easily attach to circuits
- Monochromatic light output
Single-wavelength light sources are known as monochromatic lights, where mono stands for only one and chroma for color.
Disadvantages of LED
- Voltage sensitivity
- Depends on temperature
Applications of LED
- Illumination lights for decorations and interiors
- As Indicator lights in circuits
- Barcode scanners use red LEDs instead of LASERS
- Ultraviolet LEDs for sterilization (spectra range of 220 nm to 395 nm)
- As a light source in visible light communication
- LED street lights, Lighting in cars, motor vehicles, etc
- Used in displays
- LED lighting products light up to 90% more efficiently than incandescent light bulbs.
