Introduction to Light-Emitting Diodes (LEDs)

Light Emitting Diodes (LEDs): A semiconductor device that emits visible light when an electric current passes through it.
Fundamental concept: The basic principle of the LED is Electroluminescence. It is the phenomenon of a material emitting light when an electric current or field is passed through it.
Unlike traditional bulbs, LEDs do not have a filament that will burn out or fail.

Structure and Composition of LEDs

The term LED is actually shorthand for “light-emitting diode,” which suggests the presence of a semiconductor diode.
Important components of LEDs are: an anode, a cathode, and a light-emitting semiconductor material sandwiched in between.
Common materials used for semiconductors include gallium arsenide, indium gallium nitride, and silicon carbide.

When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons.
The colour of the light is determined by the energy band gap of the semiconductor; hence LEDs are available in a variety of colours.
Unlike traditional incandescent bulbs, LEDs emit light in a specific direction, making them more efficient for certain uses such as task lighting, life span, and durability.

LEDs have a wide variety of applications, including small-scale uses like indicator lights on electronic devices and large-scale uses like big-screen video displays.
They are also used in traffic lights, vehicle brake lights, and signs due to their low energy consumption, long lifetime, and the possibility to produce them in many colours.

Advantages: Very energy efficient, long lifespan, durable, operate in cold weather, do not emit UV rays, mercury-free.
Disadvantages: High upfront costs, quality varies greatly among manufacturers, heat sensitivity.

LED technology continues to evolve, with Organic LEDs (OLEDs) now being developed, which are even more efficient, and can be used in flexible, transparent screens.
More research is being undertaken on Quantum Dot LEDs (QD-LEDs), which could potentially provide displays with significantly better colour quality.