[Physics Class Notes] on Difference Between LCD and LED Pdf for Exam

LCD

LCD stands for liquid crystal display. Liquid crystal is a kind of material that is neither liquid nor a solid, it comes in between these two states of matter. It has properties similar to that of the crystallised solid. The arrangement of molecules is in a fixed pattern however they are not fixed in shape or form.

LED

LED stands for light-emitting diode and it is a semiconductor light source that emits light when current flows through it.

It is a type of flat-panel display that uses an array of light-emitting diodes as pixels for displaying images.

It comprises two sheets of polarising material with a liquid crystal solution between them.

Full-Form of LCD and LED

LCD

This technology is used in laptops, digital clocks, watches,  digital cameras, watches, etc.

There are three types of LCD TVs

1. Flat-screen LCDs

2. Front projection LCDs

3. Rear projection LCDs

LED

They are usually found in smartphones, televisions, computer monitors and instrument panels and use a liquid crystal display panel to control where the light is displayed on your screen.

There are 3 types of LEDs based on their backlighting methods:

1. Edge-LEDs

2. Dynamic RGB LEDs

3. Full-array LEDs

Working Principle of LCD Monitor

To display anything on the screen, three major components are necessary, they are

1. Light: A source through which you see the objects.

2. Colour: To view the objects in different colours otherwise everything on the screen will appear white.

3. A way to control the light and colour on the screen.

These three components are found in LCD. 

LCD  uses liquid crystals in its main form of functioning to produce a visible image.

Principle

It is a type of flat-panel display technology that uses diodes, small cells and ionised gases for the production of images.

LCD works on the principle of blocking light.

It also works on the modulating property of light where light modulation is the technique of sending and receiving the signal through the light. 

Working

A light is non-polarized by nature when passed via a plane. It scatters in different directions and phases as you can see in the image below:

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On placing the polarization filter (either horizontal or vertical) and passing the same light through this filter. 

The filter would polarise the light in one phase and produce a clean polarised light which you can see on your computer and TV screens.

The image below shows the polarised light:

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In LCD displays, light emitted from the backlight passes via a vertical polarisation filter after going through the liquid crystal element, this liquid crystal element twists this light wave. The vertically polarised light then turns to a horizontally polarised light. This horizontally polarised light passes via the horizontal polarisation filter allowing the passage of light. Hence the light is visible to us. The voltage we apply to the LCD is applied in such a way that the crystal mechanism of the light is removed and the light acquires a straight pattern. Due to this, the vertically polarised light will come out vertically only, however, the horizontally polarised light will be blocked and we won’t see any light in this case. This is how LCD works on the principle of blocking light.

The image below shows the working of LCD:

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Difference between LCD and LED

Applications of LCD and LED

Here are some applications of LCD:

• Portable electronic games 

• As viewfinders for digital cameras and camcorders

• In video projection systems

• Electronic billboards

• Computer monitors

• Flat-panel televisions

Here are some applications of LED:

• Digital watches

• Digital computers 

• Cell phones

• Bulbs and tubes

• Automotive heat lamps

• Camera flashes 

• Calculators

• Aviation lighting

• Microprocessors 

• Burglar alarms systems

• Traffic signals

• Multiplexers