Thursday, December 1, 2011

What is the difference between LED and LCD TV?


What Is The Difference Between LED and LCD TV

A common decision pondered by many consumers when shopping for a TV is whether to buy an LCD or LED TV. However, strictly speaking they are both the same thing because an LED TV is still ‘classed’ as an LCD TV. This is because an LED TV is simply and LCD TV that uses LED lights to illuminate the LCD panel rather than fluorescent lamps which had been used prior to the introduction of LEDs. A more accurate term for describing them is LED-lit LCD TV, or simply LED LCD TV.

For your typical shopper this makes the whole LED or LCD TV argument an even more confusing affair. So why do many manufacturers categorise their TVs using the phrase LED TV?

The reason is two-fold, firstly it provides a simple way to differentiate between the two varieties of LCD technology. But also, upon the introduction of LED TVs, I’m sure that from a commercial point of view ‘LED TV’ was considered more of ‘catchy’ marketing phrase which would ultimately attract more consumers and result in more LED TVs being sold.

Anyway despite the phrase ‘LED TV’ being somewhat inaccurate, it is the term that has been widely adopted to describe an LCD TV that uses LED lighting to illuminate the display.

Unlike other ‘self-illuminating’ technologies such as OLED displays and plasma TVs where the display panel emits its own light, LCD and LED TVs require an additional light source to make the pixels of the LCD panel visible.What is an LCD backlight?

Before the introduction of the Samsung LED TV brand and its associated marketing campaign in 2009 which heavily influenced the use of ‘LED TV’ as a commonly used phrase, it is worth pointing out that TVs that used LED backlights had actually been in existence since the first Sony LED TV was released in 2004.

The Liquid Crystal Display which is used in LCD TVs is made up of a thin layer of liquid contained between two layers of glass. The liquid crystal layer is manipulated when an electric current is applied to it. In order to make the changes in the liquid crystal layer visible to the viewer, the panel is illuminated from behind and by a backlight.

Before the introduction of LED TVs, Cold Cathode Fluorescent Lamps (CCFL) was the sole method used for backlighting. The fluorescent lamps are situated horizontally behind the full width of the LCD panel. Where LED TVs differ is rather than using CCFLs they use LEDs to provide the backlight.

Types of Backlight

To complicate matters even further, the term LED TV is itself a rather broad phrase which encompasses many variations of LED TVs which employ different LED backlight technologies. There are two different types of LEDs which can be used in two different configurations, consequently this produces some distinctly differently results.

The two types of light emitting diodes used in LED TVs are white LEDs and RGB.
White LEDs actually produce a blue’ish light which is negated by using a sulphur coating to make it ‘whiter’, this results in a quality of light that is comparable to that produced by CCFLs.
RGB (red green blue) LEDs use all three primary colours to produce a broader spectrum of light in comparison to either CCFLs or white LEDs, which in turn improves the range of colors (gamut) produced by the LCD panel.

Because the LEDs are placed directly behind the LCD panel, the uniformity of the backlighting is improved in comparison to edge-lighting (see below), however it can introduce another problem known as blooming. This is when the light from a brightly lit LED zone unintentionally illuminates an adjacent dimmed area of screen covered by an adjacent zone. To the viewer a bright on-screen object can appear to have an unwanted glow around it. This backlight method can also use the RGB variety of LEDs which as explained above has a wider color gamut.Full Array LED TV with local dimming

This type of LED TV produces the best results. It involves the use of more complicated technology which also makes it the most expensive option.

Using this method the LEDs are placed in an array across the whole of the area directly behind the LCD panel. The LEDs are divided into zones which can be separately controlled so that they can be independently turned on or off. The number of LEDs and the size of the zones vary between different brands and screen sizes. This arrangement provides the ability to simultaneously increase or decrease the brightness in different areas of the display, this produces superior black levels and improved contrast.

Benefits of LED TV technology

Improved energy efficiency – Depending on which figures you believe, LED TVs are said to be 10-40% more efficient than standard LCD TVs. It is difficult to obtain an exact figure for this unless you compare a CCFL LCD with an equivalent LED TV model. Because LED TVs are more expensive they tend to have more advanced technical features such as auto-brightness and auto-power off which means they use less energy for reasons other than the improved efficiency gained from the LED backlighting itself.

Also some people would argue that the issue is overblown because the savings in electricity costs for a 60 inch LED TV in comparison to an equivalent CCFL LCD when uses for an average of 6 hours per day equates to less than $50 per year. Whilst it all helps to contribute towards reducing carbon emissions, it will take a good few years to recoup the extra investment required to own an LED TV compared to a standard LCD TV. However when comparing power consumption of LED TV vs plasma TV, LED TVs are the clear winners as they use half the power of an equivalent plasma TV.

Environment friendly – When the first Samsung LED TVs were released, as well as being more energy efficient it was claimed that the materials used in the manufacture process contained less harmful materials such as mercury. However one thing that we weren’t told is that LEDs contain other harmful materials such as arsenic and gallium.

Improved reliability – There can be no doubt that overall LED TVs are more reliable and durable than LCD TVs. The quoted lifespan of an LED TV is 100,000 hours which is approximately 50% longer than the figure for standard LCD TVs. However this equates to 11 years of continuous usage, or 30 years if used 8 hours per day making it more likely that another part of the television will fail before the LED backlighting does.

A more significant point than reliability is that CCFL backlights actually degrade in performance over time. The brightness of CCFLs as well as the whiteness of the light produced deteriorates the more the TV is used and the older the TV gets. This affects quality of the picture which may become noticeably duller before the LCD TV actually fails.


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