LCD VS. PLASMA VS. PROJECTOR DISPLAY DEVICES

LCD - Liquid Crystal Display Screens

Liquid Crystal Display (LCD) technology has been around since 1888, but it wasn''t until 1972 that the first liquid crystal display screen was manufactured. Since then LCD televisions have gone on to surpass the total number of Cathode Ray Tube (CRT) televisions sold worldwide and have dominated over 50% of the TV market share.
Recently the capabilities of LCD televisions have grown and they now offer huge widescreen displays, large viewing angles and most importantly, higher-quality pictures.

How does an LCD device work?

Televisions using Liquid Crystal Flat Panel Display are composed of two glass plates, between which lies a liquid crystal solution. To generate an image the television shines a light through the first plate, causing an electrical current to be generated among the crystals.

Each crystal reads the information in the broadcasts and consequently holds a varying amount of electrical charge, causing a certain degree of light to shine through. The final image displayed on screen is a result of this crystal formation.

Plasma Display Panel Technology

A plasma display is a type of flat panel display, which although looks similar to an LCD screen, functions very differently. Plasma display technology is a relatively new science having been first implemented in 1964 by Donald Blitzer for the PLATO Computer System.

Initially this type of display was very successful, but the introduction of CRT displays at much lower prices caused sales of plasma displays to decline sharply. Only in 1997 did Plasma display popularity begin to resurge because of the production of the first 42-inch plasma display and Pioneer''s decision to sell them to the public.

Often times Plasma televisions are confused with LCD televisions, primarily because they are both types of flat panel display technology and produce similar looking images. However, the machinery at work in these two competing technologies to generate the image is markedly different.

How does Plasma technology work?

While Plasma televisions are akin to LCD televisions in that they are made of two glass sheets, they differ in the substance "sandwiched" between them. While LCD uses a liquid crystal solution, plasma televisions hold thousands of tiny cells, each holding a mixture of neon and xenon. When the television is turned on, an electrical current runs through these cells which causes them to become electrically charged. This converts the gas into plasma. The ultraviolent light this generates excites the phosphor coating on the back of each Plasma cell, causing it to glow and output the required image.

Projector Technology

There are two common types of projector display technology -- LCD and DLP. Each functions differently in the way it produces and image and both have their own strengths and weaknesses.

DLP (Digital Light Processing) Projectors

Digital Light Processing (DLP) is a display technology developed by Texas Instruments in 1987. It is currently now one of the most frequently implemented technologies projectors use when generating an image. DLP projectors utilise thousands of tiny, microscopic mirrors placed on a Digital Micromirror Device (DMD) chip. Each mirror represents a single pixel, meaning that the resolution of the image is directly proportional to the number of mirrors present in the projector. To create the desired image the amount of light that is reflected through the lens is adjusted. To achieve this, the mirrors lean forwards and backwards in rapid motion, as directed by the image source. This varies the amount of light that is reflected through the lens.

DLP projectors are currently available in two formats, either single chip or three-chip, referring to the number of DMD chips present in the projector.

Single chip DLP projectors

To produce colours when only a single DMD chip is available, a spinning colour wheel positioned between the DMD and the projector lamp is used. This colour wheel usually consists of three colour divisions, one for each primary colour - red, blue and green. Sometimes a fourth clear, white zone that is added to the colour wheel to help boost the brightness of the image. However, since this results in a reduced colour saturation of the image, many manufacturers choose to either disable or omit this from the colour wheel.

To produce an image, single chip projectors alternate between each colour, thus producing separate red, blue and green images when projecting an image in motion. The DMD chip is synchronized with the constantly rotating colour wheel so that when the green section of the DMD is displayed when the green part of the colour wheel is positioned in front of the lamp. This means that each colour is displayed at such a fast rate that viewers will usually only see the fully composed colour image.

Depending on the rotation speed of the colour wheel used, some pictures can develop a problem known as "the rainbow effect" which is a type of image artefact that causes the viewer to see red, blue or green shadows around the edges of certain images. The degree at which this is experienced is highly dependant on the eyesight of the viewer and the picture being displayed. While some claim that this rainbow effect is ever-present, others maintain that it only occurs when their eye scans across the screen. The effect this has on viewers is similarly varied. It can cause as much as migraines in some people from just a couple of minutes viewing, where as for others it can seem to be only a very minor distraction.

Three-chip DLP projectors

The main benefit of a projector having three DMD chips is that there is a separate chip dedicated to each primary colour. Instead of using a colour wheel, three-chip projectors use a prism to direct light in each primary colour from the lamp to the corresponding DMD chip. The colours are then recompiled into one image and projected out through the lens.

Since the colours have a greater period of time to be modulated, the quality of the image is noticeably improved and colours appear more distinct. Movie theatres use these types of projectors to output films in 35 trillion different colours. Since the projector uses a prism, rather than the three optics used in single chip projectors only one optic is required. This means that the rainbow effect present in single chip projectors is non-existent.

LCD projectors

Liquid crystal display projectors are currently the most popular type of projectors on the market. Using a three panel system they can produce sharp, natural looking images as well as detailed shadows ideal for use in both home threat and business environments.

Central to how Liquid Crystal Display (LCD) projectors function is the three LCD panels, which are used to project light of each primary colour. Initially the white light from the projector lamp is separated into red, green and blue light, each of which is then passed through a dedicated LCD panel. These panels are composed of thousands of tiny pixels that are electrically charged to allow variable amounts of light to pass through them.  Each of the colours from the LCD panels is then recompiled using a prism before the projector outputs the image onto the screen. The resolution of this picture is dependant on the number of pixels each LCD panel consists of, which in recent years has grown. While 1920 x 1080 pixels (true HD resolution) is commonly available and suitable for the majority of user needs, the possibility for panels that can display a resolution of 3840 x 2610 is also available.

Comparing LCD, Plasma and Projectors

Screen size

LCD: Offers a wide range of sizes from 14 inches to 57 inches. In the coming years the maximum size available will continue to increase. Recently Sharp unveiled a 108 inch size screen although this is not currently being advertised for home use.

Plasma: Generally only available in larger sizes, ranging from 35 inches to 65 inches. Panasonic recently revealed a 32-inch screen and is committed to making smaller screens in future. However, like LCD, the main focus of manufactures is to continue to advance the maximum screen size.

Projector: The size of the image projected is variable, meaning the picture can appear 30 inches small or 300 inches large. Since there is no set size, projector specifications list screen sizes as a range i.e. 50-250 inches.

Viewing angle

LCD: Since LCD was originally designed for computer monitors, they were tailored for a user sitting exactly in front of the screen. Consequently the viewing angle of LCD screens is typically limited up to 175°. When viewed from wider angles, the image quality will degrade.

Plasma: Although Plasma viewing angles are typically capped at 178°, the way in which Plasma televisions render images means they do not suffer from as much image degradation as LCD does when viewed from wider angels.

Projector: As the light source from front projectors originates from in front of the screen, viewing angles is generally not a concern. However, the surface or screen the image is projected onto may have a small detrimental impact on the viewing.

Brightness

LCD: Although LCD televisions generally have a lower contrast ratio than Plasma, the low amount of light the screen reflects makes the image seem brighter in everyday situations.
Plasma: The technology used in plasma televisions allows for a higher contrast ratio than LCD and thus a brighter image that displays deeper, more impressive colours.
Projector: Since varying specifications are used to measure projector brightness, it is difficult to compare them directly. Projectors can now have contrast ratios of more than 50,000:1, which is almost good as LCD and Plasma. The main problem with projector brightness is the significant effect of ambient light on projected image.

Screen refresh rate

LCD: Since LCD technology was first made for computer monitors displaying static images, they initially had low refresh rates. However, modern LCD television producers have managed to implement refresh rates as low as 5ms, thus preventing the artefacts that occur on screens with a low refresh rate.

Plasma: Plasma televisions currently refresh at a faster rate  than LCD -- at a similar rate to standard Cathode Ray Tube (CRT) televisions, a standard adequate for the majority of viewers.

Projector: The pixel response time (the closest equivalent to screen refresh rate) is generally not noted on project specification sheets. This makes it hard to compare projectors to LCD and Plasma displays on this attribute. However, a general rule is that projectors marketed as home theatre projectors will render videos better than business focused projectors.

Display defects

LCD: While LCD televisions do not suffer from burn-in, they are susceptible to dead pixels. These are pixels that become fixed in either an on or off position, creating a permanent black or white dot on the screen. Although generally unnoticeable in isolated situations, if they appear in clusters dead pixels can be very distracting to viewers.

Plasma: On the other hand, while dead pixels aren''t an issue on plasma screens, if a static image is displayed on a plasma screen for an extended period of time then a shadow of the image can be burnt into the screen permanently. This can be a problem in TV channels that have logos permanently on the screen.

Projector: Although projectors are susceptible to dead pixels, numerous manufacturers cover even one dead pixel under warranty. The main display defect in projectors is the decreasing brightness that occurs the longer a lamp is used for.

Lifespan

LCD: The backlight in LCD televisions lasts between 30,000 to 60,000 hours and although replaceable, it is extremely expensive to do so.

Plasma: The typical time it takes for the lamp inside the television to reduce in brightness by 50% is around 50,000 hours. This is a figure high enough to not worry nearly every consumer.

Projector: A projector''s lamps needs to be changed fairly frequently as they last for around 2000-3000 hours. Typically a replacement lamp cost around $300, making projectors an expensive choice if intended for frequent, everyday use.

Durability

LCD: LCD televisions are more durable than plasma displays, although they should still be handled with great care and regularly cleaned.

Plasma: The fragile nature of Plasma televisions mean that it is recommendable for an expert to help install and mount the television so to avoid any potential damage.

Projector: Projector screens are typically made of fairly robust materials. In terms of the projectors themselves, they are extremely fragile since there is potential for the glass lens or lamp to crack.

Weight

LCD: LCD televisions are lighter and slimmer than Plasma televisions, making them easy to wall mount.

Plasma: The heavier weight of Plasma televisions may mean that extra support mounts by be required if mounting a large television on a wall.

Projector: Standard projectors are extremely light, typically weighing in at 20 lbs. Portable projectors are even lighter, often weighing only 10 lbs.

Shipping

LCD: LCD televisions are light and much more durable so consequently more liberty can be taken when shipping the television.

Plasma: The extra weight and fragile composition of Plasma televisions means expensive speciality carriers are a necessity.

Projector: Projectors are very small and light, meaning packaging is relatively cheap. However, due to the fragile nature of projectors they have a high potential to be damaged in transit.

Recommended applications

LCD: LCD televisions are most suitable for those seeking:

• A small (below 42 inches) sized television typically for use in bedrooms.
• The cheapest possible television if you are operating on a tight budget.
• A computer monitor.
• The most energy efficient type of television.
• A television for use with videogames that display static images on screen for long periods of time.
• A television for use in a brightly lit environment where light ambience cannot easily be controlled.
• A television to watch sports in the highest possible definition, as LCDs are typically available with higher resolutions and do not suffer from burn in.

Plasma: These televisions are most suitable for those seeking:

• A large (above 42 inches) television for use at home.
• A television for use in a home theatre that can display high contrast images.
• A television that has a wide angle viewing so many people spread out across the room can view the image clearly.

Projector: Projectors are most suitable for those seeking:

•  A device that will generate the largest, best quality image for a home theatre.
• A portable display device that can display images from laptops, a common requirement in classroom and business environments.