Final Seminar2

CERTIFICATE

Certified that Manikant Rajput (Roll No 1101720023)has carried out the work presented in this report entitled “Nuclear Battery” under my supervision. This report embodies results of original work, and preparations are carried out by the student herself.

(Mr. Manoj Kr. Kushwaha)

Assistant Professor & Head,Deptt. Of Electrical Engineering KSCEM, Bijnor

Date:

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DECLARATION

I hereby declare that this submission is my own work and that, to the best of my knowledge and belief contains no material previously composed or written by another person nor material which to a substantial extent has been accepted for the seminar of any other degree or diploma of the university or other institute of higher learning, except where due acknowledgment has been made in the text.

Signature:

Name: Manikant Rajput

Roll No.: 1101720023

Date:

ACKNOWLEDGEMENT2

Although this report prominently bears my name, it really is the result of the collaborative efforts of a number of people who have discussed, encouraged, cajoled and otherwise supported me, throughout its preparation. Firstly I would like to thank my parents and God for their blessings.

I express my heart-felt gratitude to my Seminar Incharge Sri Manoj Kr Kushwaha, Associate Professor & Head, Electrical Engineering of our college for his invaluable guidance and support throughout this work. His encouragement and constructive comments were very helpful for me to go ahead with this topic and report preparation.

I sincerely extend my thanks to some other teachers of the college for their guidance and co-operation.I owe a debt of gratitude to all my friends who are directly or indirectly supported me throughout my work.

Name: Manikant Rajput

Roll No.: 1101720023

ABSTRACT3

An LCD projector is a type of video projector for displaying video, images or computer data on a screen or other flat surfaces. It is a modern equivalent of the slide projector or overhead projector. To display images, LCD (liquid-crystal display) projectors typically send light from a metal-halide lamp through a prism or series of dichroic filters that separates light to three polysilicon panels – one each for the red, green and blue components of the video signal. As polarized light passes through the panels (combination of polarizer, LCD panel and analyzer), individual pixels can be opened to allow light to pass or closed to block the light. The combination of open and closed pixels can produce a wide range of colors and shades in the projected image.We use 3 LCD technology these days which produce far better visuals with no color separations.

TABLE OF CONTENTS

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CHAPTER 1: INTRODUCTION 6-7

CHAPTER 2: LIQUID CRYSTAL DISPLAY 8-16

2.1 LIQUID CRYSTALS 2.2 LIQUID CRYSTAL PROPERTIES AND BEHAVIOUR 2.3 MAKING A LIQUID CRYSTAL DISPLAY

CHAPTER 3: LCD TECHNOLOGY 17-19

3.1 LCD PIXELS 3.2 LCD TECHNOLOGY 3.3 3 LCD TECHNOLOGY

CHAPTER 4: LCD PROJECTOR 20-31

4.1 LCD PROJECTOR LAMPS 4.2 DICHROIC MIRRORS 4.3 LCD PANELS 4.4 PROJECTOR LENS 4.5 Dichroic Prism 4.6 LCD PROJECTOR WORKING 4.7 LCD PROJECTRO RESOLUTION 4.8 LCD PROJECTOR’S CONTRAST RATIO 4.9 LCD PROJECTOR’S ASPECT RATIO CHAPTER 5: TYPES OF LCD PROJECTOR 32 CHAPTER 6: ADVANTAGES OF LCD PROJECTOR 33

CHAPTER 7: APPLICATIONS 34

CHAPTER 8: CONCLUSION AND FUTURE ENHANCEMENT 35

REFERENCES 36

CHAPTER 1

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INTRODUCTION

1.1 GENERAL

LCD ("Liquid Crystal Display") projectors have traditionally displayed rich color saturation and image sharpness on the market. The term LCD projector encompasses all models using LCD technology, whereas "3LCD" is a trade brand and does not include some projectors. For example, there are actually a few projectors out there with four LCD panels.

There was a time when  people typically referred to most projectors as being LCD projectors, and at one point that was almost true. Today, however, most people are aware that there are three different technologies used in projectors. However, LCD projectors remain the best selling of the different technologies in use.

Virtually all LCD projectors use three separate LCD panels – each do “greyscale” not color, but one has a red, one a green, and one, a blue filter.  Ultimately the light passes through each of the LCDs with filters, and then recombines into a single beam of light... Bingo! The light shoots out through the lens and on to the screen, giving rich colors.

Of the three technologies, LCD, DLP and LCoS, no one is in all ways better than the others.  Each has distinct advantages. LCD projectors produce highly saturated colors.  In home theater space many LCD projectors add a special color filter to get the best overall color tracking.  This creates an interesting difference between the LCD projectors and the other technologies.  A typical home theater projector using LCD technology, like Epson's popular, Home Cinema 5020UB, can produce a good two thousand lumens at its brightest- unusually bright for home theater.  When we get into its best modes Cinema or THX, though, the filter slides into place, and color goes from very good to great, but down go the lumens to  about 670 lumens calibrated. In home theater space, only lower end DLP projectors that are not true "home theater" quality can match that brightness.

OK, LCD projectors designed for business and education are also particularly known for great color compared to single-chip DLP projectors. Consider though, LCoS projectors also have great color, they are usually significantly more expensive than their kin, the LCD

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projectors. Furthermore, LCD projectors are perhaps the greenest of the technologies, they get noticeably more brightness out of lamps of similar wattage, than their LCoS and DLP competition.

In the home projector market, LCD projectors tend to dominate sales in all but the most entry-level price point, which consists of all DLP projectors. LCD based projectors sold in the US start at just over $1000 for 2D models and from about $1600 for 3D capable projectors.  LCD doesn't really place in the high end space, with no popular models over $3500, yet they give many more expensive projectors some serious comptition. 

In the business, education, and government segments, (excluding pico projectors), LCD projectors outsell the other technologies, except when it comes to the very smallest and most portable projectors – under 3 pounds – that, so far seems to be primarily DLP.  On the very high end, LCD projectors offer more bang for the buck than the drastically more expensive 3-chip DLP projectors which are generally the best projectors, but you might buy a loaded 8000 lumen LCD projector for $8000, and an 8000 lumen DLP, for $25,000 or more. One "limitation" of LCD projectors on the high end. They top out around 10,000 lumens.  Those 3 chip DLP's which can hit 25,000 lumens or more are reserved for really high end installations.  You know. for lighting up screens 100 feet wide, or more.  Sorry, the brightest LCD projectors are merely bright enough for a sports arena, or major auditorium.

CHAPTER 2

LIQUID CRYSTAL DISPLAY

2.1 LIQUID CRYSTALS

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The term liquid crystal is used to describe a substance in a state between liquid and solid but which exhibits the properties of both. Molecules in liquid crystals tend to arrange themselves until they all point in the same specific direction. This arrangement of molecules enables the medium to flow as a liquid. Depending on the temperature and particular nature of a substance, liquid crystals can exist in one of several distinct phases.

Liquid crystals are composed of moderate size organic molecules which tend to be elongated, like a cigar. At high temperatures, the molecules will be oriented arbitrarily, as shown in the figure below, forming an isotropic liquid. Because of their elongated shape, under appropriate conditions, the molecules exhibit orientational order such that all the axes line up and form a so-called nematic liquid crystal. The molecules are still able to move around in the fluid, but their orientation remains the same. Not only orientational order can appear, but also a positional order is possible. Liquid crystals exhibiting some positional order are called smectic liquid crystals. In smectics, the molecular centers of mass are arranged in layers and the movement is mainly limited inside the layers.

Nematic Smectic

The nematic liquid crystal phase is by far the most important phase for applications. In the nematic phase all molecules are aligned approximately parallel to each other. In each point a unit vector can

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be defined, parallel to the average direction of the long axis of the molecules in the immediate neighborhood. This vector, known as the director, is not constant throughout the whole medium, but is a function of space.

The figure below shows the molecular structure of a typical rod-like liquid crystal molecule. It consists of two or more ring systems connected by a central linkage group.

Typical shape of a liquid crystal molecule

2.2 LIQUID CRYSTAL PROPERTIES AND BEHAVIOURS

Nematic liquid crystal media have uniaxial symmetry, which means that in a homogeneous liquid crystal medium a rotation around the director does not make a difference. The bulk ordering has a profound influence on the way light and electric fields behave in the material. Uniaxial anisotropy results in different electrical and optical parameters if considered along the director or in a plane perpendicular to it. This gives rise to interesting technological possibilities. Two unusual phenomena are the following: the reorientation of the molecules in an electric field and optical birefringence of the molecules.

Reorientation of the molecules in electric fields

As a result of the uniaxial anisotropy, an electric field experiences a different dielectric constant when oscillating in a direction parallel or perpendicular to the director. The difference is called the dielectric anisotropy. If the dielectric constant along the director is larger than in the direction perpendicular to it, one speaks of positive anisotropy.

Due to the anisotropy, the dielectric displacement and the induced dipole moment are not parallel to the electric field, except when the director is parallel or perpendicular to the electric field. As a result, a torque is exerted on the director. For materials with positive anisotropy, the director prefers to align parallel to the electric field. Liquid crystals with a negative anisotropy tend to orient themselves perpendicularly to the electric field.

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The effect of an electric field on a liquid crystal medium with positive anisotropy is illustrated in the pictures below. Originally the orientation is almost horizontal. When an electric field with direction along the blue arrow is applied, a torque (represented in green) rising from the dielectric anisotropy, acts on the molecule. The torque tends to align the molecule parallel to the field. When the field strength is increased, the molecule will reorient parallel to the field.

Original orientation Situation in electric field

Result electric field Result strong electric field

The technological importance of the reorientation is obvious: it gives a switchable medium by simply varying the applied electric field in the liquid crystal medium. In most applications a liquid crystal is used in a thin layer between two glass surfaces. To generate the electric field, thin electrodes layers are deposited on the bottom and/or top glass surface. For optical devices transparent electrodes are used, made from Indium Tin Oxide (ITO). If the generated field is strong enough, the molecules will reorient to follow its direction.

Optical birefringence

Applications of liquid crystals almost always involve optics. Optical waves also involve electric fields, but the associated frequencies are much higher than those of the fields generated by the applied voltages. Therefore the dielectric constants, which arise from the electronic response of the molecules to the externally applied fields,

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are different. To make the distinction, the refractive index is usually given for optical waves instead of the dielectric constant.

Optical waves can also reorient the liquid crystal director in an analogue manner as the electrically applied fields. In a display this can be neglected, since both the optical dielectric anisotropy and the intensity of the optical fields are typically much lower than those used in the static case. Therefore the optical transmission is mostly independent of the director calculations.

To understand the influence of birefringence on the propagation of light through a liquid crystal, the light must be represented by an electric field. This electric field is described by a wave vector in each point. At a certain time and location, the direction and the length of the vector correspond with the direction and magnitude of the electric field. For a plane wave propagating in a specific direction, the electric field vector in an isotropic medium describes an ellipse in the plane perpendicular to the propagation direction. This ellipse represents the polarization of the light. Some special cases are the linear polarization and the circular polarization where this ellipse is distorted to a straight line or a perfect circle. Generally each ellipsoidal polarization can be decomposed as a superposition of linear polarizations along two perpendicular axes. In an isotropic medium, both linear polarizations move with the same speed. The speed of the wave is determined by the refractive index of the medium.

Light propagation in an isotropic medium

For the uniaxial liquid crystal medium, an electric field feels a different refractive index when it oscillates in the plane perpendicular to the director or along the director. This uniaxial anisotropy of the refractive index is called birefringence. Birefringence allows to manipulate the polarization of the light propagating through the medium.

The elliptical polarization of light entering a liquid crystal medium must be decomposed into two linear polarizations called the ordinary

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and the extra-ordinary mode. Along these two directions, the two linearly polarized modes feel a different refractive index. Therefore, they propagate through the liquid crystal with a different speed as illustrated in the picture below.

Light propagation in a birefringent medium

In the isotropic medium, the two parts propagated with the same speed. Combining them back together will result in the same polarization ellipse as the original. In birefringent media, the different speed of the ordinary and extra-ordinary waves results in a phase difference between the two modes (= retardation). At the end of the medium this phase difference between the two oscillations will result in a different polarization ellipse.

Switchable birefringence

To observe the influence of birefringence, polarized light must be used. Most light sources such as a light bulb or a fluorescent lamp produce unpolarized light. Optical applications often required polarized light with a known oscillation direction of the light. To obtain polarized light, ordinary light sources can be used in combination with polarizers.

A polarizer is a special type of birefringent layer. The ordinary wave propagates unmodified through the medium, whereas the extra-ordinary wave is absorbed in the medium. An arbitrarily polarized wave entering such a medium will result in a linearly polarized wave at the back of the medium. In the picture above the effect of a polarizer is illustrated for two different orientations of the absorbing direction.

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Polarizer with vertical transmission axis

Polarizer with horizontal transmission axis

If two polarizers with orthogonal absorption direction are used, all light emitted by the light source is absorbed. This is typically referred to as a set of crossed polarizers.

Crossed polarizers

Birefringence is important for modifying and controlling the polarization of light propagating through the medium. A liquid crystal layer inserted between crossed polarizers can change the polarization of the light propagating through, which results in light transmission after the crossed polarizers.

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A liquid crystal layer between crossed polarizers

Because the director can be controlled using an electric field, a liquid crystal is a controllable birefringent medium. Therefore, the polarization state of the light after the liquid crystal layer can be changed and hence the intensity of the transmission through the crossed polarizers is adapted.

2.3 CREATING A LCD

To create an LCD, you take two pieces of polarized glass. A special polymer that creates microscopic grooves in the surface is rubbed on the side of the glass that does not have the polarizing film on it. The grooves must be in the same direction as the polarizing film. You then add a coating of nematic liquid crystals to one of the filters. The grooves will cause the first layer of molecules to align with the filter's orientation. Then add the second piece of glass with the polarizing film at a right angle to the first piece. Each successive layer of TN molecules will gradually twist until the uppermost layer is at a 90-degree angle to the bottom, matching the polarized glass filters.

As light strikes the first filter, it is polarized. The molecules in each layer then guide the light they receive to the next layer. As the light passes through the liquid crystal layers, the molecules also change the light's plane of vibration to match their own angle. When the light reaches the far side of the liquid crystal substance, it vibrates at the same angle as the final layer of molecules. If the final layer is matched up with the second polarized glass filter, then the light will pass through

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If we apply an electric charge to liquid crystal molecules, they untwist. When they straighten out, they change the angle of the light passing through them so that it no longer matches the angle of the top polarizing filter. Consequently, no light can pass through that area of the LCD, which makes that area darker than the surrounding areas.

Building a simple LCD is easier than you think. Your start with the sandwich of glass and liquid crystals described above and add two transparent electrodes to it. For example, imagine that you want to create the simplest possible LCD with just a single rectangular electrode on it. The layers would look like this:

The LCD needed to do this job is very basic. It has a mirror (A) in back, which makes it reflective. Then, we add a piece of glass (B) with a polarizing film on the bottom side, and a common electrode plane (C) made of indium-tin oxide on top. A common electrode plane covers the entire area of the LCD. Above that is the layer of liquid crystal substance (D). Next comes another piece of glass (E) with an electrode in the shape of the rectangle on the bottom and, on top, another polarizing film (F), at a right angle to the first one.

The electrode is hooked up to a power source like a battery. When there is no current, light entering through the front of the LCD will simply hit the mirror and bounce right back out. But when the battery supplies current to the electrodes, the liquid crystals between the

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common-plane electrode and the electrode shaped like a rectangle untwist and block the light in that region from passing through. That makes the LCD show the rectangle as a black area.

CHAPTER 3

LCD TECHNOLOGY

3.1 LCD PIXEL

Most basically LCDs produce the image you see by blocking or emitting the light from a backlight using liquid crystals sandwiched in between two glass plates. This is the same principle used in the liquid crystal displays found in everyday items such as digital watches, but improved and updated in a much more advanced implementation.

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An Exploded View of a Single LCD Pixel

An LCD display is made up of a thin layer of liquid crystals arranged in a matrix (or grid) of a million or more pixels (picture elements), which are themselves made up of three sub-pixels aligned to a colour filter for each of the primary colours; red, green and blue. This layer is sandwiched between the two glass plates, which are covered in a matrix of electrodes and transistors (electronic switches), each coated with a polarising filter. The two polarising layers only allow light vibrating in one direction to pass through them, one allows horizontally vibrating light through and the other passes vertically vibrating light.

The light source in an LCD is its backlight so this unpolarized light becomes vertically polarized as it passes through the first polarizing filter at the back of the display. The other polarizing layer on the front sheet of glass is horizontally polarized, so ordinarily the now vertically polarized light coming from backlight can't pass through it. The role of the liquid crystal layer in the middle of the display is to rotate the vertically polarized light travelling through it by ninety degrees so it can pass through the front, horizontally polarized filter. By varying the voltage applied to the liquid crystal sub-pixels the amount they twist the light changes, allowing more light of each colour though as a greater voltage is applied.

Individual pixel colours are produced by the combination of the primary colours produced by each sub pixel, with the pixel's overall brightness is produced by the sub-pixels relative intensities. Many thousands of these pixel units operating together in the display combine to produce the image you see.

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3.2 LCD TECHNOLOGY

LCD, which stands for Liquid Crystal Display, is currently the most popular type of projector technology available on the market to consumers, having gained a greater market share than the competing Digital Light Processing (DLP) technology developed by Texas Instruments. This was originally because LCD projectors were cheaper to manufacture and so were more affordable for consumers, although at the expense of a reduction in the quality of the projected image. However, recent technological advancements in projectors have seen both increases in the quality of LCD projector images and decreases in the price of DLP projector technology. Both technologies are now able to offer sharp, vibrant images at lower costs than in the past, but LCD projectors are still generally wider spread than DLP projectors.To produce an image, LCD projectors use a number of liquid crystal panels through which light is passed, unlike in DLP projectors where a Digital Micromirror Device is used.

3.3 THREE LCD TECHNOLOGY

The “3” in 3LCD refers to the number of LCD panels, or chips, used inside a 3LCD projector. When using three LCD panels each primary colour has a dedicated chip, where as one-chip projectors use a rotating colour wheel to sequentially display colours. The main advantage that 3LCD offers is that there is no “rainbow effect” which is a problem some users can experience where they perceive a

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separation of the colours which produces a rainbow like shadow on fast moving images, causing an irritating distraction. 3LCD projectors are often the choice of projectors for movie theatres since they can display up to 68.7 billion colours.

CHAPTER 4

LCD PROJECTOR

In LCD Projector, heat from the halogen bulb converts the crystal into a liquid. An LCD projector consists of various components, the details of which are listed below.

4.1 LCD PROJECTOR LAMPS

A listed lamp life of about 2000 hours is the benchmark. Some projectors also provide mode choices, for example, the 'eco-mode', which not only extends the life of the lamp; it also reduces the operating cost of the projector. The two most commonly used bulbs are the metal halide and the UHP (ultra high pressure) type because they project a very white light. The range of listed life of these bulbs is 750 to 2000 hours. While the halogen bulbs have a shorter life span and project light with a yellow tinge, xenon lamps are used in the high-end projectors

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Factors to Consider While Choosing a Lamp :

A. Check the Lamp for Brightness

If the lamp is not bright enough then we will have trouble seeing the picture when it is dark outside the room. The brightness of the lamp determines the quality of the projected image.

B. Weight of the Lamp

If we have a mounted projector then the weight of the lamp will be a point of concern. The heavier the lamp is, more the opportunity of it falling from a mount on the wall or ceiling.

C. Picture Contrast

The image quality can be greatly enhanced by adjusting the projector lamp's brightness settings. So it is important that the picture contrast of the lamp is checked before opting for it.

D. Connectivity

It is advisable that the connectivity of the lamp to the projector is considered and checked. If there is a problem in connecting the lamp it can increase the chance of the lamp breaking while trying to connect.

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E. Lamp Life

Check the lamp for its life span before buying. An average lifespan of a projector lamp is between 2000 to 4000 hours. Its lifespan also depends on how the projector lamp is used. They are quite expensive and checking the life span will help us choose wisely.

4.2 DICHROIC MIRRORS

Dichroic mirrors use the principle of thin-film interference, and produce colors in the same way as oil films on water. When light strikes an oil film at an angle, some of the light is reflected from the top surface of the oil, and some is reflected from the bottom surface where it is in contact with the water. Because the light reflecting from the bottom travels a slightly longer path, some light wavelengths are reinforced by this delay, while others tend to be canceled, producing the colors seen.

In a dichroic mirror or filter, instead of using an oil film to produce the interference, alternating layers of optical coatings with different refractive indexes are built up upon a glass substrate. The interfaces between the layers of different refractive index produce phased reflections, selectively reinforcing certain wavelengths of light and interfering with other wavelengths. The layers are usually added by vacuum deposition. By controlling the thickness and number of the layers, the frequency (wavelength) of the passband of the filter can be tuned and made as wide or narrow as desired. Because unwanted wavelengths are reflected rather than absorbed, dichroic filters do not absorb this unwanted energy during operation and so do not become nearly as hot as the equivalent conventional filter (which attempts to absorb all energy except for that in the passband)

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Dichroic mirrors of different coatings for different wavelengths

The light from the lamp passes through a series of special dichroic mirrors, which are special mirrors that only pass a certain frequency or color of light while allowing the rest of the light to pass through. This separates the white light from the lamp into its red, green and blue components. The mirrors then direct the light toward the projector's LCD panels

LP mirrors—These are long pass filter or dichroic mirror which transmits wavelengths longer than the cut-on and blocks or reflects shorter wavelengths respectively

SP mirrors—These are short pass filter or dichroic mirror which transmits wavelengths shorter than the cut-on and blocks or reflects longer wavelengths respectively

4.3 LCD PANELS

Most LCD panels used in projectors today are made of High Temperature Poly-Silicon (HTPS) which has an active matrix and is transmissive. HTPS panels are superior in that they are smaller, have higher resolution and higher contrast, and can embed drivers.The main function of HTPS is to act as a light valve for projectors. HTPS has a thin-film transistor (TFT) generated by poly-silicon in each pixel. These pixel transistors act as a conduction switch by changing the scan line's voltage. HTPS LCD panels are produced in the same way as semiconductors. They are small and highly reliable because they can

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easily be miniaturized and drivers can be generated on substrates by processing at a high temperature

HTPS Panels have transparent areas and lightproof areas.LCD (HTPS) technology concentrates light into the opening so as much light as possible penetrates the panel on the incident-side substrate. This technology has improved the brightness of panels between 1.5 and 1.6 times.

Epson’s WUXGA HTPS LCD-TFT Panel

Ultimicron Panel is Epson's latest panel which offers the resolution and fidelity needed to focus the image while providing the ability to recreate smooth gradations and a natural softness. In addition, the use of a color filter prevents the color break-up that tends to occur with other color systems when shooting fast-moving subjects and while panning.

Measuring just 0.48 of an inch diagonally, the new panel offers XGA (1024 x 768) resolution in red, green and blue for a total of 2.36 megapixels. It is the latest addition to Epson's renowned ULTIMICRON series, which already includes a 0.47-inch SVGA panel and a 0.52-inch QHD panel

Epson's ULTIMICRON Color LCD panel

4.4 PROJECTOR LENS

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Convex lenses-Fresnel lenses are mostly used in projectors. The lenses may be short throw or long throw.

Calculating throw distance: A projector’s throw distance is the distance between the projector and the image on the screen (i.e., the distance that the image is “thrown”). Throw distance is calculated by measuring the distance from the projector’s lens to the projection screen that the image is being cast onto. Throw distance is the basis for determining the projection screen size possible for use - a common standard for projector throw distances is one foot (30.5 cm) of projection screen width to every two feet (61 cm) between the projector’s lens and the screen. A smaller throw distance as opposed to a larger throw distance means a smaller possible distance between the projection screen and projector, if the size of the projected image is kept constant.

projector throw ratio

The throw ratio of a projector is the result of dividing the distance between the projector’s lens and the projection screen by the width of the image being projected, or more simply:

Screen width x Throw ratio = Throw distance

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The throw ratio figure provides projector owners with all they need to know when deciding where to place their projector or projection screen. For example, if we know that we want to use a projection screen that is ten feet wide and we know that our projector’s throw ratio is 1.8:1 (which means 1.8 ft of throw distance per foot of screen width) then we should place our projector 18 feet away from the projection screen since 10 multiplied by 1.8 equals 18.

Projectors with a built in short throw lens are highly recommended for classroom applications since these short throw lenses allow for a large size image to be projected on to the projection screen from just a short distance away. This has the added bonus of preventing light from shining in the eyes. If a standard lens is used then the projected image may appear too small to be fully visible, or blurry and out of focus at larger image sizes.

The advantages of short throw distance lenses:

A shorter throw distance will result in a bigger picture being projected, if the distance between the projector and the projection screen is kept constant. For further effect a short throw lens can be used to project an even larger image. Some projectors, such as the Hitachi X275, come pre-installed with a short throw lens and can thus project a 48-inch diagonally wide image from only 4 feet way. Projectors with short throw distances are suited to those people that require portability, such as road warriors, or for those people that need to use their projector and screen in smaller environments such as modest home theatre rooms, hotel rooms or small meeting rooms.

Optoma Short throw lens25

The advantages of long throw distance lenses:

A longer throw distance allows for smaller, sharper images to be projected from further distances away. A longer throw lens is preferable if we intend to use our projector in large, expansive surroundings such as in large conference rooms or houses of worship where the projector is required to be hidden at the back of the building. In these situations a long throw lens will most likely be required to make sure that the quality of the projected image is maintained while moving the projector further away from the screen.

Optoma Long throw lens

4.5 DICHROIC PRISM

A dichroic prism divides light into red, green, and blue, to form three pictures that utilize these corresponding colours from the LCD (HTPS) panels. Colour and image are recomposed by reflecting red and blue light and transmitting green light. The prism is formed by combining four triangular poles to create one rectangular solid. High precision is required in the processing and adhesion of poles to avoid dark lines and double images caused by misaligned dichroic surfaces.

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Dichroic prism

4.6 LCD PROJECTOR WORKING

LCD projectors employ a three-panel LCD (Liquid Crystal Display) system, referred to as 3LCD. LCD projectors crisply reproduce bright, naturally colored images that are easy on the eyes. LCD projectors are also capable of detailed shadow reproduction that is ideal for demanding business and home theater applications.

The white light from the projector lamp is split into red, green, and blue components using two dichroic mirrors, special mirrors that only transmit light of a specified wavelength. Each red, green and blue beam then passes through a dedicated LCD panel made up of thousands of miniscule pixels. An electrical current turns the panel's pixels on or off to create the grayscale equivalent of that color

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channel. The three colors are then recombined in a prism and projected through the projector lens and onto the screen.

By using a combination of three LCDs to produce a final image, LCD projectors are capable of billions of colors and smooth grayscale gradations. The resolution of the image is determined by the number of pixels in the LCD panels used. Currently LCD panels offer resolutions as high as true HD (1920 x 1080) for home theater applications. New panels promise resolutions as high as 4K (3840 x 2160).

LCDs are not just found in projectors. They are found in many of the electronics you use everyday, from a cell phone to an MP3 player to your digital alarm clock. LCDs are very common because they offer distinct advantages: they are thinner, lighter, and draw less power than many competing display technologies.

A reliable, sophisticated technology with universal appeal, 3LCD is the world's most popular projection technology, delivering high quality images for the most demanding business and consumer audiences.

4.7 LCD PROJECTOR RESOLUTION

The resolution of an LCD projector can be defined in four different categories:

* UXGA (1600 x 1200): provide very high-resolution and are very expensive. They can support a very broad range of computer equipment.* SXGA (1280 x 1024): provide high-resolution images. These projectors are targeted for people with high-end personal computers.* XGA (1024 x 768): provide relatively low-resolution images when compared to UXGA and SXGA. However, as they are less expensive, they are more popular.* SVGA (800 x 600): is the most popular resolution today because they are available at a reasonable cost and display great images. LCD projectors with SVGA are ideal for personal computer.

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Resolution – HD video signalsIn home theatre set ups the primary consideration for the projector is the quality of the projected image. One factor that drastically influences image quality is the native resolution of the projector. A higher resolution means that a greater number of pixels are displayed on screen, thus forming a sharper looking image. Projectors can output images in the 16:9 widescreen aspect ratio resolutions of 480p, 720p, 1080i and 1080p.

4.8 LCD PROJECTOR’S CONTRAST RATIO

As image quality is of central importance to home theatre viewers, contrast ratio is obviously of very high importance also. The contrast ratio figure will determine how deep the colors in the picture will appear. A typical contrast ratio is 800:1, which technically means that the darkest black on screen is 800 times brighter than brightest white. Simply put, to ensure the highest quality image, a projector with the highest possible contrast ratio is desirable. Projectors suited for use in home theatres should have a contrast ratio of at least 2500:1.

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Contrast Ratio Representation

4.9 LCD PROJECTOR’S ASPECT RATIO

A projector’s aspect ratio affects the dimensions of the image that is projected on to the screen. A widescreen 16:9 aspect ratio is preferable for projecting films since they also use a 16:9 aspect ratio. Many laptops also use this specification.

Aspect Ratio of a projection30

CHAPTER 5

TYPES OF LCD PROJECTOR

The type of projector refers to the type of display technology used on the projector. LCD's use panels of glass. DLP's use thousands of tiny mirrors.

Standard LCD - These LCD (liquid crystal display) projectors have one panel of LCD glass that controls the three primary colors. These projectors are becoming less common in the projector marketplace, as polysilicon LCD and DLP projectors gain popularity.

Polysilicon LCD - These projectors control colors through three panels and are considered to be of higher quality than standard LCD. The projection through three panels allows polysilicon LCD projectors to have higher color saturation than a standard LCD projector.

HD projectors category includes most home theater projectors. It includes both those sporting Full HD which is 1080p resolution, and 720p projectors, which, technically are just HD

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CHAPTER 6

ADVANTAGES OF LCD PROJECTOR

LCD is generally more 'light efficient' than DLP (i.e. the same wattage lamp in both an LCD and DLP would produce a brighter image through the LCD. The advantages an LCD projector has, can be discussed on certain parameters.

ENERGY EFFICIENCY

Energy efficiency has recently become an important factor for consumers and businesses alike when buying electronic devices. LCD projectors are typically more efficient with the light that the projector’s lamp produces i.e. an LCD projector will produce a brighter image than a DLP projector when using a lamp with the same wattage rating.

BRIGHTNESS LEVEL

Images appear to have a greater saturation when projected using LCD technology, meaning that although a corresponding DLP projector might have a higher contrast ratio, the same projection on an LCD projector may appear brighter.

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No RAINBOW EFFECT

No rainbow effect in LCD projectors. In terms of disruptions to image quality, LCD projectors are not affected by screen burn-in, picture processing noise, or “the rainbow effect” which is often seen in single chip DLP projectors using a color wheel.

ACCURATE COLORS

With 3LCD projectors, we get beautiful color in clear, defined images. These projectors do not have a color wheel.

CHAPTER 7

APPLICATIONS

Common situations where projectors are used or the environments in which LCD projectors are needed include:

Classrooms for education-Instructors supplement their lecture material with PowerPoint presentations shown with an LCD projector and computer.

Corporate boardrooms and training facilities-The presentation on various developments and growth in a company can be presented in an easy way.

Personal home theatre set ups- we can see movies even in our homes and feel as if we are watching in a multiplex.

Houses of worship Bars, clubs and pubs

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Each type of application will have a series of key considerations which should be focussed on when deciding on which projector to purchase for use in that application.

CHAPTER 8

CONCLUSION AND FUTURE ENHANCEMENT

LCD Projectors are the latest developments which digital technology is offering. Even as technology enhancements have increased, projector prices have decreased, and now projectors are used in a variety of situations for numerous different purposes. Advances in LCD technology have mainly been aimed at reducing the “screen door” problem. These include:Higher resolutionsReductions in the gap between pixelsThe use of Micro- Lens Array (MLA) to boost the efficiency of light transmission through XGA-resolution LCD panels

Edge-Guided Resolution Enhancement in Projectors via Optical Pixel Sharing is also a new technique which can increase the resolution of the projector without increase in the price.

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Therefore, with the recent LCD technology developments, we may say that in near future we may see LCD projectors everywhere in our daily life for education, entertainment, office, even at home.

REFERENCES

1. Edge-Guided Resolution Enhancement in Projectors via Optical Pixel Sharing, http://www.ics.uci.edu/~gopi/SamplePubs/pixelshare.pdf

2.http://en.wikipedia.org/wiki/Dichroic_prism

3.http://www.quadrantsolutions.com/Projectors/Projection-Accessories/Projector-Lenses

4.http://lcp.elis.ugent.be/tutorials/lc/lc3

5.http://www.fujitsu.com/downloads/MICRO/fma/pdf/LCD_Backgrounder.pdf

6. Liquid Crystal Displays: Fundamental Physics and Technology by Robert H Chen. ISBN: 978-0-470-93087-8

7. http://www.bambooav.com/throw-distance-and-throw-ratios-explained.html

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8. http://lcp.elis.ugent.be/tutorials/lc/lc2

9.http://professional.sony.ca/projectors/guides/understand_3lcd_tech.pdf

10. http://seminarprojects.com/s/3lcd-technology-pdf

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