DIFFERENCE B/W LED & LCD DISPLAY

PREPARED BY, G.INFANT

GOPINATH, M.SC(S/E),

PMU.

WHAT IS AN LED?

LED Light Emitting Diode. An LED is a two-lead(a lead is an electrical connection

consisting of a length of wire that comes from a device.) semiconductor light source.

It is a p-n junction(it is a interface between two types of semiconductor namely p-type and n-type inside a single crystal of semiconductor) diode, which emits light when activated.

P-n Juntion is created by Doping. when a suitable voltage is applied to the leads, the

electrons are able to recombine with electron holes within the device, releasing energy in the forms of photons.

This effect is called electroluminenescenes.

The color of the light (corresponding to the energy of the photon) is determined by the energy band gap(energy gap) of the semiconductor.

LEAD

LED DISPLAY An LED display is a flat panel

display,which uses an array of light-emitting diodes as pixels for a video display.

the LED's brightness in also used for outdoors in destination sign on public transport vehicles.

HISTORY OF LED DISPLAY The first LED flat panel television screen

was developed by James P . Mitchell in 1977.

BENIFITS OF AN LED DISPLAY Energy efficient - LED’s are now capable of outputting

135 lumens/watt Long Lifetime - 50,000 hours or more if properly

engineered Rugged - LED’s are also called “Solid State Lighting

(SSL) as they are made of solid material with no filament or tube or bulb to break

No warm-up period - LED’s light instantly – in nanoseconds

Not affected by cold temperatures - LED’s “like” low temperatures and will startup even in subzero weather

Directional - With LED’s you can direct the light where you want it, thus no light is wasted

Excellent Color Rendering - LED’s do not wash out colors like other light sources such as fluorescents, making them perfect for displays and retail applications

Environmentally friendly - LED’s contain no mercury or other hazardous substances

Controllable - LED’s can be controlled for brightness and color

DRAWBACKS OF AN LED DISPLAY LEDs are more expensive than conventional

lighting technologies , They must be supplied with the correct voltage and current at a constant flow , And this requires some electronics expertise to design the electronic drivers .

LEDs can shift color due to age and temperature , And two different white LED will have two different color characteristics, So , They  affect how the light is perceived .

WHAT IS LCD?

A liquid-crystal display (LCD) is a flat-panel display or other electronic visual display that uses the light-modulating properties of liquid crystals. Liquid crystals do not emit light directly.

 LCD televisions are thinner and lighter than Cathode Ray Tube (CRTs) of similar display size, and are available in much larger sizes. 

The light was provided by a series of cold cathode fluorescent lamps (CCFLs) at the back of the screen.

use white or colored LEDs as backlighting instead. Millions of individual LCD shutters, arranged in a grid,

open and close to allow a metered amount of the white light through. Each shutter is paired with a colored filter to remove all but the red, green or blue (RGB) portion of the light from the original white source. 

Liquid crystals encompass a wide range of (typically) rod-shaped polymers that naturally form into thin, ordered layers, as opposed to the more random alignment of a normal liquid. 

LCD LAYERS Polarizing filter film with a vertical axis to

polarize light as it enters. Glass substrate with ITO electrodes. The

shapes of these electrodes will determine the shapes that will appear when the LCD is turned ON. Vertical ridges etched on the surface are smooth.

Twisted nematic liquid crystal. Glass substrate with common electrode film

(ITO) with horizontal ridges to line up with the horizontal filter.

Polarizing filter film with a horizontal axis to block/pass light.

Reflective surface to send light back to viewer. (In a backlit LCD, this layer is replaced with a light source.)

ADVANTAGES OF LCD Brightness: Produces very bright images

due to high peak intensity. Very suitable for environments that are brightly lit .

Emissions: Produce considerably lower electric, magnetic and electromagnetic fields than CRTs.

Geometric Distortion: No geometric distortion at the native resolution. Minor distortion can occur for other resolutions.

Screen Shape: Completely flat screen.

Power Consumption: Energy efficient. Consume less than 1/3 the power of a comparable CRT. Consume less electricity than a CRT and produce little heat.

Physical Aspects: Take up about 40% less desk space. LCDs are thin and compact.

Sharpness: At the native resolution, the image is perfectly sharp. Adjustments are required at all other resolutions which can result in measurable degradation to the image.

DISADVANTAGES OF LCD Aspect Ratio: The aspect ratio and resolution are fixed. Black-Level: Not proficient at producing black and very

dark grays. In a "standard" configuration, not appropriate for use in dimly lit and dark conditions.

Contrast: Lower contrast than CRTs due to a poor black-level.

Color and Gray-Scale: AccuracyColor saturation is reduced at low intensity levels due to a poor black-level. Images are satisfactory, but not accurate due to problems with black-level, gray-scale and Gamma.

CostConsiderably: more expensive purchase price than comparable CRTs . (Cheaper lifetime cost: lasts about 13,000 - 15,000 more hours than a typical CRT.)

Gray-Scale: Have an irregular intensity scale and typically produce fewer than 256 discrete intensity levels. For some LCDs portions of the gray-scale may be dithered.

Motion Artifacts: Slow response times and scan rate conversion result in severe motion artifacts and image degradation for moving or rapidly changing images.

Resolution: Works best at the native resolution. The native resolution can not be changed. All other resolutions require adjusting procedures which can cause considerable deterioration of the image.

Viewing Angle: Restricted viewing angles. Viewing angles affect the brightness, contrast and colors shown. Wide angles can lead to contrast and color reversal.

White Saturation: Saturation and compression can occur due to the bright-end of the intensity scale becoming overloaded. Contrast control must be carefully adjusted.

Thank U…