liquid crystal display main page

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LIQUID

CRYSTAL

DISPLAY

SUBMITTED BY-

SHRUTI KAUSHIK

SECTION-

260

ROLL NO-

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TABLE OF CONTENTS

SNO TOPIC PAGE

NO

1 what is lcd 8

2 Technology

behind lcd

monitor

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3 Working of lcdmonitor

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4 Features of lcd

television

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5 Diff between lcd

and plasma

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6 Texas

instruments test

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7 High

transmissive tft

lcd technology

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8 Challenging

technologies for

lcd

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9 Conclusion

10 Refrences

FIGURES

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FIG 1PAGE 8

FIG 2PAGE 9

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FIG4PAGE 11

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FIG 7PAGE18

FIG 8PAGE15

ABSTRACT

A liquid crystal display (LCD) is an electro

optical amplitude modulator realized as a

thin, flat display device made up of any

number of color or monochrome pixels

arrayed in front of a light source or reflector.

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There are 2 types of LCD that is PASSIVEMATRIX and ACTIVE MATRIX LCD.LCscan be aligned by electric and magneticfields .one electro optical affects with LCsrequires a current through the LCs cell; all

other practiced electro optical affects onlyrequire an electric field(without current) forthe alignment of LC.

LCD television now uses liquid crystalscaptivated between two polarized glasssheets and a matrix of TFT (thin filmtransistor) transistors that control the electricflow through the crystals .The glass sheetcontains thousands of tiny cells or pixels andeach one is colored with green blue or red.

The performance of LCD can be improvedwhat is llcd(RGB) light emitting diodesinstead of cold cathode fluorescent lamps inedge lit LCD backlights brightness and colorperformance (gamut) of LCD displays.

In present daily life some other technologieshave entered this feild which have betterfeatures than LCD technology like DLP(Digital liquid processing) and CRT (cathoderay tube).Presently it is being challenged by

PLASMA television. The main differencebetween LCD and DLP is being presented inthe project .Texas Instruments experimentclearly describes the difference between LCDand DLP technology.

INTODUCTION

In the following project a detail explanationabout what is LCD and what are the featuresof LCD are being depicted.LCD is a display

device that uses thin, flat sheet made up ofliquid crystals and this thin sheet is placed infront of a light source. The molecules ofliquid crystal are twisted in their natural stateand allow the light to pass through. However,when certain amount electricity passesthrough liquid crystals, the molecules getstretched and block the light and the

darkening of the pixels depends on theelectric current. Pixels are completelydarkened when there is no electricity.

As for colour LCD display, it will have three

sub-pixels (green, blue and red) anddepending on the pixels that get light, theLCD will produce the final image on thescreen.

WHAT IS LCD.???????

A liquid crystal display (LCD) is an electrooptical amplitude modulator realized as athin, flat display device made up of anynumber of color or monochrome pixels

arrayed in front of a light source or reflector.

It is often utilized in battery-poweredelectronic devices because it uses very smallamounts of electric power.

.

Figure 1

Above picture represents us ReflectiveTwisted Nematic liquid crystal display.

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The main features of this particular liquidcrystal display are as follows:-

Glass substrate with ITOelectrodes. Theshapes of these electrodes will determine the

shapes that will appear when the LCD isturned ON. Vertical ridges etched on thesurface are smooth.

1. Twisted nematic liquid crystal.2. Glass substrate with common

electrode film (ITO) with horizontalridges to line up with the horizontalfilter.

3. Polarizing filter film with a horizontalaxis to block/pass light.

4. Reflective surface to send light backto viewer.

An example of LCD:-

LCD monitor

Liquid Crystal display or LCD monitor is athin and flat device for display. It is made bylarge number of color or monochromaticpixels which are arrayed in way of a lightsource or a reflector.

TECHNOLOGY BEHIND LCD

MONITOR

Figure 2

Liquid Crystal display or LCD monitor is athin and flat device for display. It is made bylarge number of color or monochromatic

pixels which are arrayed in way of a lightsource or a reflector. It uses very smallamount of electric power and hence is usedoften in battery powered electronic devices.The technology used is very much dissimilarto CRT technology which is used by manydesktop monitors. It was used only onnotebook computers for a very long time.Only recently they have been offered as analternative to CRT monitors. They take upvery less desk space and are much lighterthan the CRT monitors. But they are alsoquite expensive.

Each pixel of LCD monitor display has alayer of aligned molecules between twoelectrodes which are transparent and twopolarizing filters. Because there is no liquidcrystal between the aligned polarizing filters,light which has passed through the first filterwill be blocked by the second polarizer. Thesurface which is in contact with the crystal istreated to align it in particular direction. Thedirection of alignment is defined by directionof rubbing.

Resolution, in terms of horizontal andvertical size expressed in pixels, is nativesupported for the best display effects. This isone of the things that sets LCD monitor apart.

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Dot Pitch is defined as the distance betweentwo adjacent pixels. It is the minimum forsharper image. Each pixel is divided intothree cells, or sub pixels. These are coloredred, green and blue. Each sub pixel can be

controlled independently for millions ofcombinations and hence colors. Older CRTmonitors use phosphors for sub pixelstructure. The analog electron beam thoughdoes not hit the exact sub pixel.

Color components can be arrayed in variousgeometries, depending on how the monitor isto be used. If the software being used knowsthe geometry, it can be used to increase theapparent number of pixels using sub pixel

rendering. This kind of technique is oftenused in text anti-aliasing. LCDs which areused in digital watches and calculators haveseparate contact for each segment. Thus anexternal dedicated circuit charges eachsegment individually. This is not possible ifthe number of elements increases.

Small monochrome displays like the onesused in Personal Organizers or in olderlaptops have passive matrix like structure andemploy super twisted nematic or double layerSTN technology. Here, each row or eachcolumn has a single electrical circuit andthe pixels are hence addressed according torows and columns. But as the number of pixels increases, the response timedecreases and the technique no longerremains feasible.

Color displays used in modern LCDmonitors and televisions use active matrixstructure. An array of thin film transistors(TFT) is added. Each pixel has a dedicatedtransistor. Active Matrix display looksbrighter and sharper than passive matrixdisplay of similar size and has betterresponse time.

LCD technology has some critical drawbacks

too. Resolution of a CRT monitor can bechanged without introduction of any newartifact. But LCDs can produce only theirnative resolution and non native resolutionsare achieved by scaling. The blacks of LCDs

are actually grey because of presence of alight source. This results in lower contrastratio when compared to CRTs. LCDs withcheaper parts cannot display as many colors plasma or CRT counterparts.

Also, LCD display has longer response timewhen compared to Plasma or CRTcounterparts. Input lag is also present and theviewing angle is limited. In spite of thesedrawbacks, LCD display is quickly gaining

prominence.

WORKING OF A LCDTELEVISION

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HOW DOES A LCD TELEVISIONWORK??

LCD television uses liquid crystals captivated between two polarized, glass sheets and amatrix of TFT (thin-film transistor)transistors that control the electric flowthrough the crystals. The glass sheet containsthousands of tiny cells or pixels and each oneis coloured with green or blue or red.

There is a florescent bulb which sits rightbehind the glass pixels and illuminates thesecells. Each pixel has a TFT transistor next to

it that determines how much it should beelectrically charged. Less the pixel iselectrically charged, more light beams itallows and greater the intensity of respectivecolour on the LCD screen. Thus, the light beams are either blocked off or shown indifferent amounts so the combination of allpixels produce the image on the screen,

FEATURES OF LCDTELEVISION:-

Screen resolution

The native or screen resolution determineshow much sharp the picture will look on thescreen. CRT type TVs work well withstandard definition and can show pictures of330 lines resolution.

FIGURE 4 represents the LCD resolution

Figure 4

The screen resolution of LCD TV starts from720p and higher (1080i and 1080p). Thismeans its higher native resolution ensuresthat picture looks sharper, more detailed andclearer.

LCD Screen and profile

Typically, LCD TV screen size variesbetween 26" and 40" although larger screensizes are available at expensive price tags.Currently, the largest LCD TV available incommercial market has about 52" screen sizeand the models will be very few.

LCD TV is a bit thinner (less than 3"thickness) and also weighs much lesser thanplasma TV so it can be hung on the wall.

Wide Aspect Ratio

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LCD TV looks typically rectangular as itsscreen supports 16:9 aspect ratio, which isthe standard screen format of high definitionvideos. However, home videos and standardTV broadcast still use 4:3 aspect ratio so all

LCD TVs are designed to automatically fit4:3 aspect ratio images to its screen so yousee the picture filling the entire screen.

FIGURE 5 represents us a CRT Televisionwith 4:3 Aspect Ratio on the other handFIGURE 6 represents us a LCD Televisionwith 16:9 Aspect ratio.

Figure 5

Figure 6

COLOUR DISPLAY

Figure 6 (A SUBPIXEL OF COLOUR LCD)

In color LCDs each individual pixel isdivided into three cells, or sub pixels whichare colored red, green, and blue, respectively, by additional filters (pigment filters, dyefilters and metal oxide filters). Each sub pixelcan be controlled independently to yieldthousands or millions of possible colors foreach pixel.CRT monitors employ a similar'sub pixel' structures via phosphors, althoughthe electron beam employed in CRTs do nothit exact 'sub pixels'.

Color components may be arrayed in variouspixel goemetries, depending on the monitor's

usage. If the software knows which type ofgeometry is being used in a given LCD, thiscan be used to increase the apparentresolution of the monitor through sub pixelrendering. This technique is especially usefulfor text anti-aliasing.

To reduce smudging in a moving picturewhen pixels do not respond quickly enoughto color changes, so-called pixel overdrivemay be used.

DIFFERENCE BETWEENPLASMA AND LCDTECHNOLOGY

Plasma and LCD panels may look similar,but the flat screen and thin profile is where

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the similarities end. Plasma screens , uses amatrix of tiny gas plasma cells charged byprecise electrical voltages to create a picture.LCD screens (liquid crystal display) are inlayman's terms sandwiches made up of liquid

crystal pushed in the space between two glass plates. Images are created by varying theamount electrical charge applied to thecrystals.

Both plasma and LCD sets produce excellent pictures, although many homeentertainment specialists and gamersstill say CRTs produce the bestoverall images

improved significantly -- so much so that thedifferences in performance between LCDsand plasmas in this regard is almostnegligible

The biggest advantage plasmas have had overtheir LC cousins is price. In the past 12

months , things have changed, with LCDsmatching or even beating plasmas in bothresolution and price. Plasmas being sold inAustralia generally run between 42-inchesand 63-inches wide, with the cheapeststandard definition 42-inch selling forapproximately AU$2,300 (although you canexpect to find sets cheaper than AU$2,000 inreal world prices). 60-inch and aboveplasmas can go for as much as $25,000.

LCDs, on the other hand, generally top outaround the 52-inch mark -- though there isnow a ludicrously expensive 70-inch sonyavailable -- but are incredibly competitivewith similar-sized plasmas.

ADVANTAGES OF LCD

OVER PLASMA

Apart from being price competitive, LCD hasthe edge over plasma in several other keyareas. LCDs tend to have higher nativeresolution than plasmas of similar size, whichmeans more pixels on a screen.

There are no sources in the currentdocument.LCDs also tend to consume less power than plasma screens, with someestimates ranging that power saving at up to30 per cent less than plasma. LCDs are alsogenerally lighter than similar sized plasmas,making it easier to move around or wallmount.

LCD pundits also point to the fact that LCDs

have a longer lifespan than plasma screens.This was true of earlier plasma models,which would lose half of their brightnessafter more than 20,000 hours of viewing.Later plasma generations have bumped thatup to anything between 30,000 and 60,000hours. LCDs, on the other hand, areguaranteed for 60,000 hours.

You might have also heard that plasmassuffer from screen burn in, an affliction not

as commonly associated with LCDs. Screenburn in occurs when an image is left too longon a screen, resulting in a ghost of that imageburned in permanently. Newer plasmas areless susceptible to this thanks to improvedtechnology and features such as screensavers, but burn-in is still a problem.

DO PLASMA HAS A

GREATER MARKET

VALUE OR LCDPlasmas give you more bang for your buck

at the big end of town, and while LCDs cangive you better resolution, plasma still hasthe edge in terms of picture quality. Oneother thing to look for, whether you opt for plasma or LCD, is an integrated tuner --

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many TVs still have analogue tuners, whichlook pretty terrible on a large screen.

At the smaller end of things (15" to 42"TVs), LCD is the only way to go if you want

something slim and tasteful. And the bestthing is that LCDs are getting cheaper all thetimes.

EXPERIMENT DEPICTING

DIFFERENCE BETWEEN

PLASMA AND LCD

TECHNOLOGY

Texas Instruments' Test : DLP vs.

LCDEvan Powell, July 2, 2003

THIS EXPERIMENT GIVES US THE

MAIN DIFFERENCE BETWEEN DLP

AND LCD TECHNOLOGY

Texas Instruments had examined the

reliability of the DLP and LCD technologies.The test results seemed to indicate that DLP-based projectors deliver stable picture qualityover their expected usable life, whereas LCDprojectors may be expected to degrade overtime.

MAINFRAME OF THE EXPERIMENT

Texas Instruments commissioned a lab test tocompare the relative stability and longevity of

the DLP and LCD technologies. The testcommenced in May, 2002. Two DLPprojectors and five LCD projectors were run24 hours a day, 7 days a week for fivemonths, with breaks only to change lamps asneeded. During this time each projector was periodically measured for lumen output,contrast, uniformity, and color chromaticity

for white, red, green, and blue.

The test was sponsored by TI and the testitself was conducted at the Munsell color

science Laboratory (MCSL)

Description of the Lab Test

The test was conducted at the facilities of theMunsell Color Science Laboratory inRochester, NY. It was carried out in adedicated 10 x 18 foot room. Eight projectorswere operated essentially 24 hours per day, 7days per week. These included the two DLPprojectors and five LCD projectors alreadynoted, plus an LCOS-based projector. Thetechnical performance data pertaining to theLCOS machine was not included in the finalreport issued by TI since a sample of one isnot sufficient to support any conclusionsabout the technology.

The two DLP and five LCD machines were portable-class machines. Six of the sevenunits (both DLPs and all but one of the LCDs)were XGA resolution. The fifth LCD unit was

16:9 format of unspecified resolution. Thefive LCD projectors consisted of three with0.9" panels and two with 0.7" panels. TheDLP units represented one each of 0.9" and0.7" chips. Both DLP projectors were rated at2000 ANSI lumens. The five LCDs hadbrightness ratings of 800, 1000, 1100, 2000,and 2000 ANSI lumens.

The eight units in the test were placed infairly close proximity, from a minimum of 4

to 5 inches, to as much as a foot or moreapart. They were placed on three shelves oneabove another, with several units on eachshelf. They were arranged in a manner toprevent the hot exhaust of one unit feeding theintake vent of another. At the end of eachshelf a fan was installed to blow air across all

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units on that shelf. The objective of these fanswas to distribute cool air from the airconditioning vents as evenly as possible over allunits.

The room was cooled by a central airconditioning unit operated by a wall-mountedthermostat located about 10 to 12 feet fromthe projectors. Average ambient temperaturein the room during the test was 25 degrees C,or 77 degrees F. The actual temperaturevariance range around the average any givenpoint in time was about ten degrees F, fromjust under 75 degrees to the mid-80's.

Temperatures rose and fell in this range withthe cycling of the air conditioning system.

The projectors were run round the clock sevendays a week, with downtime for the changingof lamps and filter cleaning/replacement asnecessary. They were all fed the samecomputer data signal with rotating graphicimages to prevent burn-in. Technical

performance measurements were taken atdays 0, 1, 2, and 4; weeks 1, 2, and 4; andmonths 2, 3, 4, and 5.

Results of the Texas Instrument

test

At the end of about 4700 hours of operation,TI summarized the results as follows:

1. Full On/Off, and ANSI contrast degraded

over time on all five LCD units, but remainedrelatively constant on the two DLPs.

2. The optical degradation seen in the LCDswashed the picture out and raised the darklevels.

3. Color chromaticity remained stable on theDLPs, but significant changes were seen inthe LCDs. There was a visible yellowing ofthe image on all the units, and some later

developed a "blue blemish" as well.

4. The pattern of degradation was the same onall five LCD products tested. The degradationoccurred first in the blue channel. TI's theoryis that the organic compounds in the polarizerand LCD panel were breaking down underexposure to high frequency blue and UV light.Eventually there are signs of breakdown inthe red and green channels as well.

5. The first of the LCD projectors to fail was judged by TI personnel to have reached anunacceptable condition in 1368 hours ofoperation. Subsequent failure of the other fourunits occurred at 2160, 2352, 3456, and 3456hours.

Based on these test results, TI suggests that afundamental flaw exists in LCD technologythat causes the picture quality it delivers todeteriorate well before the end of life of the

projector itself might be expected. BecauseDLP technology is allegedly immune todegradation, it is purported to offer a lowercost-of-ownership since DLP projectors donot need to be replaced as often as LCD-basedproducts.

Conclusion

Manufacturers recognize that the organiccompounds in LCD panels and polarizers aresusceptible to high heat and light energystress, and will eventually break down ifdeployed in high stress environmentsin particular 24x7 operation with higher thannormal ambient temperatures. Compact portable LCD projectors are in general not

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recommended for 24x7 duty cycles because ofthis.

On the other hand, DLP technology does not

use organic compounds. Thus the elementswhich can be expected to degrade over timeunder high stress in an LCD projector do notexist in a DLP projector. Therefore whenthese two technologies are placed side-by-sidein an unusually high stress environment asthey were in this test, the DLP-based productsshould be more resistant to image shift overtime. TI's test demonstrated this in nouncertain terms.

We agree with TI's assessment that highintensity blue and UV light in the bluechannel contributes to accelerated breakdownof the organic compounds in that channel.However degradation due to high intensitylight is not normally expected to occur at therates documented in the test unless thecomponents are subjected simultaneously toabnormally high heat stress. Therefore wesuspect that 24x7 operation, higher thannormal ambient temperatures, and the close

proximity of the test units to one another mayhave combined to create abnormal conditionsthat led to a more rapid and severedegradation of the components than userswould typically experience.

Thus the generalized inference that manyobservers have drawn from the test data,which is that LCD technology itself may beexpected to routinely break down undernormal usage before the expected lifespan of

the projector, is difficult to sustain based uponthe limited sample size and the abnormalconditions we believe may have existed in thelab.

The test at Munsell Color Science Lab clearlydraws attention to the fact that LCD

technology has a failure mode that does notexist with DLP, and that failure modebecomes readily apparent in an unusually highstress environment. What the test does not tell

us is how much of a problem this really is inreal life.

HIGH TRANSMISSIVE

ADVANCED TFT LCD

TECHNOLOGYIntroduction

Today transmissive TFT LCDs have beenmainly used for digital camera and digitalvideo camera displays.However, transmissive TFT LCDs need tosecure at least 350 cd/m2 or greater screenbrightness to achieve good visibility underbright sunlight. It leads to the increase ofpower consumption. On the other hand,

transflective TFT LCDs are mainly used forcellular phones. In a transflective LCD, a partof the transmissive area is used as a reflectivearea, thus the transmissive area decreases.Consequently, the colorfilter that is 1.5 to 2 times as bright as thoseof transmissive LCDs have been adopted forachieving high brightness. Thus the colorreproduction area that can be displayed isnarrowed by transmittance of CFsincreases. This is because that higher priority

has been given to power consumption thandisplay quality forcell phones.

Advanced TFT

Pixel Structure and Its Features

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The division ratio of the transmissive areaand the reflective area can be optionally set,and if the transmissive area is set bigger thanthe reflective area, display characteristicswith priority given to transmissive mode are

obtained, and if the reflective area is setgreater than the transmissive area, displaycharacteristics with priority given toreflective mode are obtained.This divisionratio should be determined in accord with theproducts to which the display is mounted. Forexample, for clamshell-typecellular phones the priority is given to displayquality rather than power consumption, andthe latter can beapplied to straight-type cellular phones to

which priority is given to low powerconsumption. The transmissive area and thereflective area can be set by forming thetransmissive electrode and the reflectiveelectrode inside the pixel electrode on theTFT substrate. In the transmissive area, atransparent ITO electrode that allows lightfrom the backlight to transmit is formed,while in the reflective area, a highreflectivityaluminum electrode that reflects the ambientlight entering from the observer side isformed. In addition, MRS (micro reflectivestructure)3)4) is adopted on the aluminumelectrode surface. Therefore, it ispossible to design the light so that it scatterswithin a range of specified angles, and highreflectance can be obtained by efficientlyutilizing the ambient light.On the other hand, the distance of the lightthat passes the liquid crystal layer of thereflective area and transmissive area can bemade equal by making the liquid crystal ofthe transmissive area about two timesthicker than the liquid crystal of the reflectivearea. When the liquid crystal thickness of thetransmissivearea is set equal to that of the reflective areaand the reflectance is set to the maximum as ,the transmittance is about 50% of thetheoretical value. On the other hand, by

making the path of the light that passes theliquid crystal layers of the reflective area andthe transmissive area equal, thetransmittance and reflectance can be achievedthe maximum value respectively. In order to

form different thickness of liquid crystalbetween the reflective areaand the transmissive area, it makes a bumpformed by arranging an insulation layer inonly the reflective area on TFT substrate(multi-gap structure on TFT substrate).However, with this structure, the edge of theinsulation layer that corresponds to theboundary section between the transmissivearea and the reflective area does notcontribute to either transmittance or

reflectance.

Figure 7 and Figure 8

(Display image of High- TransmissiveAdvanced TFT LCD Technology)

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CHALLENGING

TECHNOLOGIES FOR LCD INTODAYS TIME(CRT ANDDLP)

Cathode ray tube (CRT) display and liquid

crystal display (LCD) were compared for

their suitability in visual tasks. For this

purpose visual performance was assessed by

means of a search task carried out using both

displays with different levels of ambient

light. In addition, suitability was rated

subjectively by users of visual display units

(VDUs). Error frequency for search tasks

carried out using LCD were significantly

smaller when compared to error frequency

for tasks at CRT. LCD gave rise to 34% less

errors than did CRT. Reaction time in search

task was found to be significantly shorter

using LCD when tasks were carried out in

darkness. Subjective rated suitability of LCD

was scored twice as high as suitability of

CRT. Results indicate that LCD used in this

experiment may give better viewing

conditions in comparison to CRT display.

DLP VS LCD TECHNOLOGY

The Technical Differences between LCD

and DLP

LCD (liquid crystal display) projectorsusually contain three separate LCD glasspanels, one each for red, green, and blue

components of the image signal being fedinto the projector. As light passes through theLCD panels, individual pixels ("pictureelements") can be opened to allow light topass or closed to block the light, as if eachlittle pixel were fitted with a Venetian blind.This activity modulates the light andproduces the image that is projected onto thescreen.

DLP ("Digital Light Processing") is aproprietary technology developed by TexasInstruments. It works quite differently thanLCD. Instead of having glass panels throughwhich light is passed, the DLP chip is areflective surface made up of thousands oftiny mirrors. Each mirror represents a singlepixel.

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In a DLP projector, light from the projector'slamp is directed onto the surface of the DLPchip. The mirrors wobble back and forth,directing light either into the lens path to turnthe pixel on, or away from the lens path to

turn it off.

In very expensive DLP projectors, there arethree separate DLP chips, one each for thered, green, and blue channels. However, inDLP projectors under $20,000, there is onlyone chip. In order to define color, there is acolor wheel that consists of red, green, blue,and sometimes white (clear) filters. Thiswheel spins between the lamp and the DLPchip and alternates the color of the light

hitting the chip from red to green to blue. Themirrors tilt away from or into the lens pathbased upon how much of each color isrequired for each pixel at any given momentin time. This activity modulates the light andproduces the image that is projected onto thescreen.

The Advantages of LCD Technology

One benefit of LCD is that it has historically

delivered better color saturation than you getfrom a DLP projector. That's primarilybecause in most single-chip DLP projectors,a clear (white) panel is included in the colorwheel along with red, green, and blue inorder to boost brightest, or total lumenoutput. Though the image is brighter than itwould otherwise be, this tends to reducecolor saturation, making the DLP pictureappear not quite as rich and vibrant.However, some of the DLP-based hometheater products now have six-segment colorwheels that eliminate the white component.This contributes to a richer display of color.And even some of the newer high contrastDLP units that have a white segment in thewheel are producing better color saturationthan they used to. Overall however, the best

LCD projectors still have a noteworthyperformance advantage in this area.

LCD also delivers a somewhat sharper imagethan DLP at any given resolution. The

difference here is more relevant for detailedfinancial spreadsheet presentations than it isfor video. This is not to say that DLP isfuzzy--it isn't. When you look at aspreadsheet projected by a DLP projector itlooks clear enough. It's just that when a DLPunit is placed side-by-side with an LCD ofthe same resolution, the LCD typically lookssharper in comparison.

A third benefit of LCD is that it is more light-

efficient. LCD projectors usually producesignificantly higher ANSI lumen outputs thando DLPs with the same wattage lamp. In thepast year, DLP machines have gotten brighterand smaller--and there are now DLPprojectors rated at 2500 ANSI lumens, whichis a comparatively recent development. Still,LCD competes extremely well when highlight output is required. All of the portablelight cannons under 20 lbs putting out 3500to 5000 ANSI lumens are LCD projectors.

The Dsadvantages of LCD Technology

LCD projectors have historically had twoweaknesses, both of which are more relevantto video than they are to data applications.The first is visible pixelation, or what iscommonly referred to as the "screendooreffect" because it looks like you are viewingthe image through a screendoor. The secondweakness is not-so-impressive black levelsand contrast, which are vitally importantelements in a good video image. LCDtechnology has traditionally had a hard timebeing taken seriously among some hometheater enthusiasts (understandably) becauseof these flaws in the image.

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While an XGA projector uses about 589,000pixels to create a 16:9 image, a WXGAprojector uses over one million. At this pixeldensity, the screendoor effect is eliminated atnormal viewing distances.

Second, the inter-pixel gaps on all LCDmachines, no matter what resolution, arereduced compared to what they use to be. Soeven today's inexpensive SVGA-resolutionLCD projectors have less screendoor effectthan older models did. The third developmentin LCDs was the use ofMicro-Lens Array(MLA) to boost the efficiency of lighttransmission through XGA-resolution LCDpanels. Some XGA-class LCD projectors

have this feature, but most do not. For thosethat do, MLA has the happy side effect ofreducing pixel visibility a little bit ascompared to an XGA LCD projector withoutMLA. On some projectors with this feature,the pixel grid can also be softened by placingthe focus just a slight hair off perfect, apractice recommended for the display ofquality video. This makes the pixels slightlyindistinct without any noticeable compromisein video image sharpness.

Now when it comes to contrast, LCD stilllags behind DLP by a considerable margin.But recent major improvements in LCD'sability to render higher contrast has keptLCD machines in the running among hometheater enthusiasts. All of the LCD projectorsjust mentioned have contrast ratios of at least800:1. They produce much more snap, betterblack levels, and better shadow detail thanthe LCD projectors of years past were able todeliver.

The Advantages of DLP Technology

There are several unique benefits that arederived from DLP technology. One of themost obvious is small package size, a featuremost relevant in the mobile presentation

market. Since the DLP light engine consistsof a single chip rather than three LCD panels,DLP projectors tend to be more compact. Allof the current 3-pound miniprojectors on themarket are DLPs. Most LCD projectors are

five pounds and up.

Another DLP advantage is that it can producehigher contrast video with deeper blacklevels than you normally get on an LCDprojector. DLP has ardent followers in thehome theater world primarily due to this keyadvantage.

While both technologies have seenimprovements in contrast in the past two

years, DLP projectors still have acommanding lead over LCDs in this regard.Leading-edge LCD projectors like the SonyVPL-VW12HT is rated at 1000:1 contrast,and Sanyo's PLV-70 is rated at 900:1.Meanwhile, the latest DLP products gearedtoward home theater are rated as high as3000:1. Less than two years ago the highestcontrast ratings we had from DLP were in therange of 1200:1.

This boost in contrast is derived from TexasInstrument's newer DLP chip designs, whichincrease the tilt of the mirrors from 10degrees to 12 degreees, and features a blacksubstrate under the mirrors. These changesproduced a significant advance in contrastperformance that simply did not exist before.

A third competitive advantage of DLP overLCD is reduced pixelation. These days it ismost relevant in the low priced, lowresolution SVGA class of products. In SVGAresolution, DLP projectors have a mutedpixel structure when viewed from a typicalviewing distance. Conversely, most SVGA-resolution LCD projectors tend to have amore visible pixel grid. This is entirelyirrelevant if you are using the projector forPowerPoint slide presentations. However, it

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is more problematic for a smooth videopresentation. For this reason, we don'tnormally recommend SVGA-resolution LCDprojectors for home theater. Conversely, therevolutionary is a DLP-based SVGA

resolution projector. It is selling now forunder $1,000 and is an incredible deal for thehome theater enthusiast on a limited budget.

In XGA and higher resolution, DLPtechnology pretty much eliminates pixelvisibility from a normal viewing distance.However, the latest WXGA resolution LCDsdo so as well. So with higher resolutions,differences in pixelation are not the bigcompetitive battleground they used to be.

DLP continues to hold a small competitiveedge, but the dramatic advantage of DLPover LCD no longer exists. The screendooreffect is receding into history as a problem ofdays gone by.

A Potential Problem with DLP: The

Rainbow Effect

If there is one single issue that people pointto as a weakness in DLP, it is that the use of a

spinning color wheel to modulate the imagehas the potential to produce a unique visibleartifact on the screen that folks refer to as the"rainbow effect," which is simply colorsseparating out in distinct red, green, and blue.Basically, at any given instant in time, theimage on the screen is either red, or green, orblue, and the technology relies upon youreyes not being able to detect the rapidchanges from one to the other. Unfortunatelysome people can. Not only can some folkssee the colors break out, but the rapidsequencing of color is thought to be theculprit in reported cases of eye strain andheadaches. Since LCD projectors alwaysdeliver a constant red, green, and blue imagesimultaneously, viewers of LCD projectorsdo not report these problems.

How big of a deal is this? Well, it is differentfor different people. For some who can seethe rainbow effect, it is so distracting that itrenders the picture literally unwatchable.Others report being able to see the rainbow

artifacts on occasion, but find that they arenot particularly annoying and do not inhibitthe enjoyment of the viewing experience.Fortunately, the majority of the populationeither cannot detect the rainbow artifacts, orif they can they are not overly bothered bythem. The fact is if everyone could seerainbows on DLP projectors the technologynever would have survived to begin with,much less been embraced by so many as agreat technology for home theater video

systems. Nevertheless, it can be a seriousproblem for some viewers.

Texas Instruments and the vendors who buildprojectors using DLP technology have madestrides in addressing this problem. The firstgeneration DLP projectors incorporated acolor wheel that rotated sixty times persecond, which can be designated as 60Hz, or3600 RPM. So with one red, green, and bluepanel in the wheel, updates on each color

happened 60 times per second. This baseline60Hz rotation speed in the first generationproducts is also known as a "1x" rotationspeed.

Upon release of the first generationmachines, it became apparent that quite a fewpeople were seeing rainbow artifacts. So inthe second generation DLP products the colorwheel rotation speed was doubled to 2x, or120Hz, or 7200 RPM. The doubling of therefresh rate reduced the margin of error, andso reduced or eliminated the visibility ofrainbows for many people.

Today, many DLP projectors being built forthe home theater market incorporate a six-segment color wheel which has twosequences of red, green, and blue. This wheel

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still spins at 120Hz or 7200 RPM, butbecause the red, green, and blue is refreshedtwice in every rotation rather than once, theindustry refers to this as a 4x rotation speed.This further doubling of the refresh rate has

again reduced the number of people who candetect them. Nevertheless it remains aproblem for a number of viewers even today.

CONCLUSION

From the above detailed explanation aboutLCD technology I have concluded that LCDis a growing technology . LCD technologywill be used in many fields like HighPerformance LCD Blacklighting using highintensity Red,Green and Blue light emittingDiodes.

In future LCD technology will be overcomedby latest DLP technology which is inventedby TEXAS INSTRUMENT. As DLP have

small package size. DLP consists of onesingle chip than 3 in LCD Panels.DLP panelsare more compact than LCD.

DLP can produce higher contrast video withdeeper blacklevels than we get in LCDprojectors.

REFRENCES

1) What is LCD?? Fromwww.wikipidia.com

2) Technology behind LCD monitorFromwww.lcdtv.me.uk

3) Working of LCD television Fromwww.buzzle.com

4) Features of LCD television Fromwww.wikipidia.com

5) Texas Instruments Test

Fromwww.projectorcentral.com6) High Transmissive Advanced TFTLCD TechnologyFromwww.google.com

7) Challenging Technologies for LCD intodays Time Fromwww.projectorcentral.com

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