What is a Plasma Display?

Plasma Displays are flat panel TV's that use plasma to create a coloured light. Millions of small compartments - "bulbs" or "cells" - are spaced between two pieces of glass, each with a mixture of gases. The inside wall of each "cell" is coated with coloured phosphors - Red, Blue or Green - which give of light when exposed to other light. When electricity is passed through the gas atoms, ultraviolet photons are given off, therefore triggering the phosphors to light up, resulting in stunning vivid colours and ultra-clear pictures being produced. Depending on the phosphors used, different colours of light can be achieved.

Each pixel is made up of three "subpixels", each with a different coloured phosphor. These colours blend together to create the overall colour of that specific pixel. By varying the current flowing through each cell, the intensity of each pixel and subpixel can be changed to produce hundreds of combinations of colours across the whole spectrum.

What is an LCD Display?

LCD stands for Liquid Crystal Display. This contradictory name is explained by understanding that liquid crystals are neither a solid nor a liquid, but a substance existing in a state between the two. At any point, liquid crystals can be in a "substate", somewhere between a solid and liquid - the most important here being Nematic . In the Nematic state, the liquid crytals are a bit like liquid - the molecules can move around and shuffle past one another but all point broadly in the same direction (Imagine shaking matches in a matchbox!). Nematic liquid crystals adopt a twisted structure, and can be straightened out with the application of electricity - the key to LCD's turning pixels on and off!

The LCD display has a backlight, and in front of this there are millions of pixels (made up of three subpixels, 1 red, 1 blue and 1 green). Each pixel has a polarizing filter in front and behind it, and between these filters is a twisted nematic liquid crystal which can be untwisted with electricity. When untwisted, the light is able to flow through the filters and lighten up the pixel.

What is an LED Display?

LED stands for Light Emitting Diode. A real LED screen tends to be used as a large display at events such as concerts and sporting venues as they have been designed specifically to be visible in bright sunlight. Confusingly, LED screens have been introduced by manufacturers and suppliers as smaller displays for the home and business market, but these are NOT actually LED screens, rather LCD screens with LED backlighting. LED has become the common name for these displays.

These LED displays use liquid crystal compressed between glass, as in LCD's, but unlike LCD's, the backlight is made of hundreds of LEDs instead of a fluorescent lamp. There are two types of LED lighting; direct and edge. Direct lighting has the ability to turn sections of the lighting off allowing for better contrast, whereas edge lighting allows the chassis to be very thin.

Remember, LED displays are LCD technology with LED backlighting, and are NOT to be confused with OLED - organic light emitting diode.

Contrast Ratio

The contrast ratio of a display describes the ability to show the brightest colours and darkest colours on the screen at the same time.

The contrast ratio is often increased by manufacturers by dynamically altering backlight brightness, allowing extra detail to be shown in dark pictures. It is widely thought that Plasma displays have a better contrast ratio than LCD's, due to the fact that plasma displays can totally deactivate the light source for individual areas of the screen. LED display technology allows the display to individually control backlit segments, therefore producing a similar contrast ratio to Plasma displays. However, some LED displays are "edge-lit" (usually slimmer) and therefore have a lower contrast ratio than the backlit LED displays.

Viewing Angle

The viewing angle of a display is the range in which the image can be viewed with no loss of contrast or colour.

A wide viewing angle is important if the display is to be viewed by multiple people simulteneously i.e. in a meeting room. Plasma displays are thought to have better viewing angles than LCD and LED displays, although this is not always the case so panels should be compared directly against each other if possible. LCD's can suffer from colour shift and loss of brightness. LED displays have better viewing angles than LCD's due to the backlight distribution.

Colour

Colour is largely dependent on the specific screen, model and manufacturer.

Plasma displays can, in theory, produce brighter colours overall. LED backlit displays offer a larger colour range than traditional LCD screens due to the improved brightness of the light source, although colour accuracy can be adjusted on most screens.

Motion

Fast motion can cause blur and jitter on displays, therefore it is important to choose the correct display for your use.

There is much controversy over which display type is better to handle fast motion. A plasma display has the ability to refresh each individual subpixel at a much faster rate than LCD displays, and therefore is often thought to handle fast motion well, free of blur. However, new LCD displays can now update the image displayed 100 times per second (double the standard 50Hz rate) therefore removing much of the blur from the LCD display image. New generation technology of LCD displays will double the refresh rate to 200 times per second, although this is currently unavailable. LED displays use the same processing as LCD displays, currently with a refresh rate of 100Hz. As LED displays are the current new display technology, they will usually employ the most up to date type of motion processing technology.

Power

Plasma, LCD and LED displays all require power although some offer significant power savings over others.

Most LCD's require a single backlight to be powered. Plasma displays require every subpixel to be powered individually, therefore consumes more power than LCD's. A plasma display may use up to 50% more power than the equivalent sized LCD! LED displays offer significant power savings over both other display types, due to energy efficient backlighting. LED displays may consume 40% less energy than an LCD display!

Life

The lifespan of a display relies on various factors such as the life of a backlight, image burn in issues and the life given by manufacturers.

In the past, plasma displays suffered from short lifespans, and image burn issues. If users were to leave a static image on the screen, the plasma cells would retain this image and it would effectively "burn" the screen, although screensavers, power shutdown features and improvements in technology means this issue is now rarely seen. The life of LCD's depends on the life of the backlight, which are often rated above 60,000 hours. New LED displays have expected lifespans of over 100,000 hours. LCD and LED displays do not experience any of these problems found in Plasma technology.

Price vs Screen Size

It is tempting to simply pick the cheaper of either a plasma or LCD screen when you have decided on the size of the display, BUT...