04.Plasma vs LCD
What is plasma?
A plasma screen is made up of very small gas-filled cells, called sub-pixels, which emit ultraviolet light when an electric current is passed through them. They’re arranged in groups of three, each coated with either red, green or blue fluorescent material that glows when the gas is excited. These groups of three are called pixels. It’s the small size and large number of these cells that give the plasma screen a more detailed image than the more traditional TV screen.
Pros
- Picture quality is generally good and cm for cm they're usually cheaper than LCD screens
- They’re very thin (often less than 10 cm) for their width and height
- They have a flat screen, which means no distortion at the edges
- Uniform screen brightness when they’re new and probably for life if properly cared for.
- They can be wall-mounted in some situations.
- The 16:9 aspect ratio is well suited to both DVDs and digital TV broadcasts.
- No image distortion from speakers. A plasma screen is unaffected by strong magnetic fields, so you can put your speakers as close as you like.
- They can accept a wide range of input signals, including most TV signals (PAL, NTSC and SECAM) and have a number of input types, such as standard RCA jacks, S-video, component video and HDMI. Also, most will accept output from a computer via RGB inputs.
Cons
- Check warranties and how much help you’ll get installing it at home.
- Pixels aren’t repairable. If one or more cells stop working and you find it noticeable, you may have to have the whole thing replaced.
- Plasma screens can suffer from ‘burn-in’. This is where a static image on the screen for long periods can become semi-permanent. It is more likely to be a problem early in the screens life but may be reversible by displaying an even grey screen for a time. Also, if you watch a lot of 4:3 aspect ratio TV (including free-to-air TV) on a plasma screen, the cells in the middle will age more quickly than those on the edges, which in extreme cases could lead to uneven brightness over time.
- They’re heavy despite being thin. Typically a 106 cm screen (measured diagonally) weighs anything from 29.5 kg to 45 kg, the latter about the same as a normal 68 cm TV.
- They produce heat when operating and may have a built-in fan to help with cooling. Listen to it with the sound off in a quiet room to make sure it isn’t distracting in quiet sections of a movie.
- If you live in a very hot part of the country, be aware that most manufacturers suggest operating temperatures below 35°C or 40°C.
How long will plasma last?
- Estimates vary from as low as 10,000 to more than 60,000 hours.
- At around four hours’ viewing a day that equates to seven and 41 years respectively, which is more than you’d expect from a normal TV. However, these figures are based on an even loss of brightness and don’t take into account the possibility of one group of cells aging more quickly than those around them, which would result in an irreversible darker spot. This is a real possibility if you were to watch a lot of free-to-air television or play computer games in 4:3 format.
- Generally warranties vary from one to five years and most exclude pixels that malfunction (unless there’s more of them than the manufacturer deems acceptable), burn-in and heat-related problems.
- The number of dead pixels that’ll be covered isn’t always stated. Since the other warranties we’ve seen are vague in this area, using phrases like “within normal commercial tolerance” to describe pixel failure. The retailer should explain the manufacturer’s pixel policy before you buy a plasma screen. If they don’t and you find noticeable dead pixels, they’re obliged to replace the screen.
What is LCD?
Liquid crystal displays are also made up of sub-pixels, but unlike plasma screens the LCD sub-pixels don’t emit light, they act like a blind allowing light through from a backlight in varying degrees. Colour is produced by filters in front of each sub-pixel to produce red, green or blue.
Pros
- LCDs are slim and relatively lightweight compared to plasmas. Most LCDs can be mounted on a wall, occupying less space and keeping them out of toddler reach. You may need to buy a wall-mounting kit though.
- LCDs can be quite bright which makes them suitable for well lit rooms.
- LCDs can be made at quite small sizes and most TVs less than 106cm are LCD these days
- With the introduction of LED back lighting some LCD TVs have become very efficient on terms of power usage when operating
Cons
- LCDs don’t have as good blacks as plasma because the backlight tends to leak through somewhat. However, this problem is being addressed and is generally less apparent with newer models.
- Dead pixels: This is the main drawback of LCDs. LCDs are made up of hundreds of thousands of them, and if one gets stuck in one particular form (say as a particular colour) it’s said to be dead. While you won’t see one dead pixel from a normal viewing distance, a clump of them in one area would be visible as a spot on your screen. It’s worth checking manufacturers’ warranty conditions for dead pixels when you’re buying.
- LCDs are relatively expensive, but getting closer to plasma costs all the time.
LCD with LED
There's some confusion over what LED really means for television. Currently most LCD TVs have a backlight which is similar to a compact fluorescent light called a CCFL (cold cathode fluorescent lamp). This is a reasonably efficient light source, but once the TV is turned on it remains at the same brightness and draws power at pretty much the same level regardless of what's on the screen. This has the effect of making it harder to get a good black because light tends to "leak" through the LCD panel.
LED backlighting has two main advantages:
1. It appears from our testing so far, to use less power.
2. It's possible to vary the light intensity very quickly so light levels can be reduced in dark scenes, which in turn produces better black levels.
However, LED actually comes in two forms:
• Side lit LED where the light source comes from an array of LEDs around the screen. This is the cheaper option and can have some issues with evenness of lighting and viewing angles.
• Back lit LED where there's an array of LEDs across the back of the screen. This is claimed to produce a better picture quality, but there are very few TVs of this sort in the market at present and they tend to be expensive.
OLED (Organic Light Emitting Diode) is a technology that may make its way into mainstream TVs in the future. Currently there's only one in the market and it's an 11inch (28cm) Sony model priced at around $7000.
The ‘nits’ and bolts
- Screen brightness is usually referred to in units of measurement called candelas per square metre (cd/m2) or sometimes nits (1 nit = 1 cd/m2). The more nits, the brighter the picture.
- A normal TV has a screen brightness between 600 and 800 nits. If an ordinary TV looks OK in your room, a plasma screen of similar brightness will probably be OK. Be careful, though: some manufacturers don’t list the screen brightness and we’ve seen some as low as 300 nits.
- Resolution is often quoted because plasma and LCD TV screens can have more 'dots per inch' than normal TV screens and can therefore more accurately represent DVD and digital TV broadcasts. If you want the best in high-definition digital TV (HDTV) you’ll probably opt for a more expensive screen with 1920 x 1080 pixels. However, lower definition 1024 x 768 can still do the job nicely.
- Display: A standard-definition digital TV (SDTV) signal has 576 lines per screen, each made up of 720 pixels. It’s sometimes referred to as 576i and any plasma screen is capable of displaying it. This signal is displayed on a normal TV using a system called interlacing (hence the ‘i’ in 576i). Each picture is created with two passes of the TV’s electron gun, each pass of the gun covering only half the lines on the screen. One HDTV signal (called 576p) has the same resolution as SDTV but without interlacing, so you get the whole picture in one go.
- Plasma and LCD screens don’t have guns and passes, and they usually display the image all in one go. However, you may get varying image quality depending on the source and the screen’s resolution. If the number of pixels from the source (such as a TV broadcast or DVD) doesn’t match the resolution of the screen, it will be converted by the screen’s onboard scan rate converter to match. This may result in slight variations in quality from one source to another.