power point presentation on led

8/4/2019 Power Point Presentation on LED

http://slidepdf.com/reader/full/power-point-presentation-on-led 1/19



A light-emitting diode (LED) isa semiconductor light sourceavailable acrossthe visible, ultraviolet and infrared

wavelengths, with very highbrightness.

There are major 3 types of displaysbased on LED

1. Light-emitting diode (LED)based displays

2. LED-backlit LCD televisiondisplays

3. Active-matrix OLED



Drawbacks of CRT Display Large size and weight, especially for bigger

screens (a 20-inch (51 cm) unit weighs

about 50 lbs (23 kg) High power consumption Generates a considerable amount of heat

when running

Produces noticeable flicker at low refreshrates

Color displays cannot be made in sizessmaller than 7 inches



The first true all LED flat panel television TVscreen was developed, demonstrated anddocumented by J. P. Mitchell in 1977. Themodular, scalable display was initially

designed with hundreds of MV50 LEDs anda newly available TTL memory addressingcircuit from National Semiconductor

The ¼ in thin flat panel prototype and thescientific paper were displayed at the 29thISEF expo sponsored by the Society for Science and the Public in Washington D.C.May 1978.



CRT DisplayFlat Panel LED Display



•An LED-backlight LCD television is an LCD television, flatpanel display that uses LED backlighting instead ofthe Cold cathode (CCFL) used in traditional LCDtelevisions. It is not a true LED display but is called "LEDTV" by some manufacturers.

•The use of LED backlighting has a dramatic impact,resulting in a thinner panel, less power consumption andbetter heat dissipation, and a brighter display with bettercontrast levels.

The LEDs can come in three forms :1) Dynamic RGB LEDs2) White Edge-LEDs3) A full-array of LEDS



RGB dynamic LEDs positioned behind the panel.

This method of backlighting allows dimming to occur in

locally specific areas of darkness on the screen. This can

show truer blacks, whites at much higher dynamic

contrast ratios.

White Edge-LEDs positioned around the rim of thescreen using a special diffusion panel to spread the

light evenly behind the screen (the most common).



This method of backlighting allows for LED-backlit TVs to

become extremely thin. The light is diffused across the

screen by a special panel which produces a uniformbrightness distribution across the screen.

A full-array of LEDS which are arranged behind the

screen but are incapable of dimming or brighteningindividually.

Many brands use LED backlighting technology and may

offer a range of benefits over CCFL LCD TVs such as

reduced energy consumption, better contrast and

brightness, greater colour range, more rapid response

to changes in scene and a capacity to provide the

means to render an image more accurately.



Produce images with greater dynamiccontrast.

With Edge-LED lighting they can be extremely

slim. Models on the market can beapproximately one inch thick.

Offer a wider color range when RGB-LEDbacklighting is used.

Less environmental pollution on disposal. Higher price.

Generally 20-30% lower power consumption.

Improved reliability.



LED backlights are often dimmed by applying pulse-widthmodulation to the supply current, switching the backlightoff and on again like a fast strobe light.

If the frequency of the pulse-width modulation is too lowand or the user is very sensitive to flicker, this may causediscomfort and eye-strain, similar to the flicker of CRT

displays. This can be tested by a user simply by waving a hand or

object in front of the screen. If the object appears to havesharply-defined edges as it moves, the backlight is strobingon and off at a fairly low frequency. BUT…

If the object appears blurry, the display either has acontinuously-illuminated backlight or it is operating at afrequency that is too high for the brain to perceive.

The flicker can be reduced or eliminated by setting thedisplay to full brightness, though this has a negative impacton image quality and battery life due to increased power consumption.



Active-matrix OLED (active-matrix organic light-emitting

diode or AMOLED) is a display technology for use in mobiledevices and televisions. OLED describes a specific type of thinfilm display technology in which organic compounds formthe electroluminescent material, and active matrix refers tothe technology behind the addressing of pixels.

OLED: An organic light emitting diode (OLED) is a light-emitting diode (LED) in whichthe emissive electroluminescent layer is a film of organiccompounds which emit light in response to an electriccurrent.

AMOLED technology is used in mobile phones, media playersand digital cameras and continues to make progress towardlow-power, low-cost and large-size (for example 40 inch)applications.



An active matrix OLED display consists

of a matrix of OLED pixels thatgenerate lightupon electrical activation that havebeen deposited or integrated ontoa thin film transistor (TFT) array, whichfunctions as a series of switches tocontrol the current flowing to eachindividual pixel.

Typically, this continuous current flow iscontrolled by at least two TFTs at eachpixel, one to start and stop thecharging of a storage capacitor andthe second to providea voltage source at the level neededto create a constant current to thepixel and eliminating need for the very

high currents required for passivematrix OLED operation



Magnified image of theAMOLED screen on the

Google Nexus One

TFT backplane technology is crucial inthe fabrication of AMOLED displays.

Two primary TFT backplanetechnologies, namely polycrystallinesilicon (poly-Si) and amorphoussilicon (a-Si), are used today inAMOLEDs.

These technologies offer the potentialfor fabricating the active matrixbackplanes at low temperatures(below 150°C) directly onto flexibleplastic substrates for producing flexible AMOLED displays



Lower cost in the future

Light weight & flexible plastic substrates Wider viewing angles & improved

brightness

Better power efficiency Faster response times:200 Hz, theoretically

have less than 0.01 ms response timeenabling 100,000 Hz refresh rates.

Active-matrix OLED displays provide higher refresh rates than their passive-matrix OLEDcounterparts, and they consumesignificantly less power



Current costs

Shorter Lifespan

Efficiency of blue OLED(20% red,19% ofgreen, blue only 4-5%)

Water damage

Outdoor performance Screen burn-in

UV sensitivity



Thinner & better displays in TV ,monitors

In Smartphone &mobile devices’ display

power point presentation on led

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