Difference Between LCD and LED for JEE Main 2025

Explain LCD and LED: In today's technologically driven world, Liquid Crystal Display (LCD) and Light-Emitting Diode (LED) screens dominate the landscape of visual displays. From televisions and computer monitors to smartphones and digital signage, these two technologies have become an integral part of our daily lives. Understanding the underlying principles that govern LCD and LED technology not only enhances our appreciation for these displays but also allows us to make informed choices when selecting the most suitable option for our needs. In this article, we will know about LCD and LED differences, starting from knowing the LCD and LED full form. To do that first, we need to deal with the question, “What is LCD and LED?”. Then, we will learn about the characteristics of LCD and LED.

Defining LCD

Liquid Crystal Display (LCD) is a display technology that operates on the principles of physics, specifically the manipulation of light by liquid crystals. In an LCD, a layer of liquid crystal molecules is sandwiched between two layers of transparent electrodes, forming what is known as a liquid crystal cell. Some characteristics of LCD are listed below:

• Liquid Crystals: Liquid crystals are organic compounds that possess a state of matter that lies between that of a solid and a liquid. They exhibit a molecular structure that exhibits both liquid-like fluidity and the ordered alignment of solid crystals when subjected to an electric field. This alignment affects the way light passes through the liquid crystal layer, enabling the creation of images.

• Polarised Light: LCDs utilize polarised light to generate images. When light passes through a polarising filter, it becomes polarised, meaning its electric field oscillates in a specific direction. The liquid crystal layer in an LCD can rotate the polarisation of light by applying an electric field, controlling the amount of light that can pass through.

• Electric Field Manipulation: An essential component of LCD technology is the transparent electrodes that apply an electric field to the liquid crystal layer. By applying a voltage, the electric field causes the liquid crystal molecules to align in a particular direction, altering their optical properties.

• Polarizers: LCD screens employ polarizers, which are filters that only allow light with a specific polarisation to pass through. A polarizer is placed on the front surface of the display and another at the back, with their polarisation axes perpendicular to each other. This configuration blocks out all light when there is no electric field applied to the liquid crystal layer.

• Backlighting: To provide illumination for LCD displays, a separate light source called a backlight is placed behind the liquid crystal layer. This backlight emits white light that passes through the liquid crystals, colour filters, and polarizers, resulting in the formation of the visual image.

• Colour Generation: LCDs produce colours by incorporating colour filters. The liquid crystal cells are combined with red, green, and blue colour filters to create individual subpixels. By adjusting the electric fields applied to each subpixel, the intensity of each colour can be controlled, allowing for the reproduction of a wide range of colours.

Understanding these fundamental physics principles behind LCD technology allows us to appreciate the complexity of these displays. It also explains various characteristics of LCDs, such as their ability to produce high-quality images, their relatively low power consumption, and their limited viewing angles.

Defining LED

Light Emitting Diode (LED) is a semiconductor device that converts electrical energy directly into light through a process called electroluminescence. Some characteristics of LED are listed below:

• Semiconductors: LEDs are made from semiconductor materials, typically compounds such as gallium arsenide (GaAs), gallium phosphide (GaP), or gallium nitride (GaN). Semiconductors have a specific band gap energy, which determines the colour of light emitted by the LED.

• Electroluminescence: In a semiconductor, there are two energy bands: the valence band and the conduction band, separated by the bandgap energy. Electrons in the valence band have lower energy, while those in the conduction band have higher energy. For an LED to emit light, electrons need to transition from the conduction band to the valence band using the process known as electroluminescence.

• Band Gap: In a semiconductor, there exists a region called the band gap, which represents an energy barrier that separates the valence band (where electrons normally reside) and the conduction band (where electrons are free to move). The energy difference between these two bands determines the wavelength and colour of light emitted by the LED.

• Carrier Injection: When a forward voltage is applied to an LED, electrons from the n-type semiconductor (which has excess electrons) and holes from the p-type semiconductor (which has missing electrons) are injected into the active region of the LED. The active region is typically a narrow layer of another semiconductor material.

• Radiative Recombination: As electrons and holes combine in the active region, they recombine with each other, releasing energy in the form of photons. The energy of these photons corresponds to the bandgap energy of the LED material, determining the colour of light emitted.

• Efficiency: LEDs are known for their high efficiency compared to traditional light sources. This efficiency is due to the direct conversion of electrical energy into light, minimising energy losses as heat.

• Colour Control: The colour emitted by an LED can be tuned by adjusting the composition and band gap energy of the semiconductor material. By using different semiconductor materials or adding dopants, LEDs can emit light across a broad spectrum, ranging from ultraviolet to infrared.

Understanding the physics of LEDs allows us to comprehend their key features, such as their energy efficiency, long lifespan, and ability to provide a wide range of colours. 

LCD and LED Difference

LCD vs LED can be shown in the table below:

Summary

From this article, it can be concluded that Liquid Crystal Display (LCD) is a display technology that operates on the principles of physics, specifically the manipulation of light by liquid crystals, whereas LLight Emitting Diode (LED) is a semiconductor device that converts electrical energy directly into light through a process called electroluminescence. Understanding the physics behind LCD and LED displays allows for informed decisions when choosing displays based on factors such as energy efficiency, image quality, viewing angles, and cost.