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TV Tech - Turning in the Tube (Part 1)

Posted September 19, 2013 9:00 AM by cheme_wordsmithy

My TV needs an upgrade…

Really?! Coming from the guy whose still owns [only] a flip phone, types on an 8-year-old IBM ThinkPad, and plays his video games and music on an old Dell Dimension desktop? Yep, sure is.

(CRT TV - Via 1800recycling.com)

Though I'm sure many of you from the CR4 community could outdo me on old-tech retainage, it is still a stretch for me to spend my hard earned $ for an HDTV, when a perfectly good CRT television is still chugging away in my living room. But what can I say? I love the beauty of a high-def picture. And I love my movies.

But starting my quest to find the right TV for the right price was much more involved than I thought it would be. To start, I thought it best to familiarize myself better with the science behind the two prominent TV technologies on the market today: LED-LCD and Plasma. Here's a rundown of what I picked up:

TV Display: The Basics

To begin, it behooves me to say that all TVs at their simplest level work in the same way -they take an electric current and use it to produce or manipulate light at the pixel (or sub-pixel) level. A pixel is the smallest item of information in a digital image inside a computer or TV panel-i.e.,it is one of the thousands of little dots on your computer monitor or TV screen. Each pixel is made up of three "sub-pixels" - one red, one green, one blue. These colors mix in different amounts to create the desired color, and thousands of pixels with different colors combine on the display to create an image.

The difference between different TV technologies lies in the process used to create the lighting in each pixel.

LED LCD TVs

Liquid Crystal Display (LCD) TVs use liquid crystals-molecules that can be manipulated by an electric current. The LCD screens consist of two polarizing filters (one horizontal and one vertical), with a layer of liquid crystals contained between two glass plates. When an electric current is applied, the liquid crystal aligns in a way that either allows light through or blocks it out. The light then travels through a color filter (red, green, or blue) and each grouping of the three colors makes up one pixel. A thin film transistor layer is present underneath the liquid crystal matrix which acts as a mechanism to rapidly switch pixels on and off.

Layers of an LCD panel Viadigitaltrends.com

LCDs are referred to as transmissive displays because light is actually transmitted through the display rather than inside the panel.There are two lighting sources used in LCD displays: traditional fluorescent (known as cold-cathode fluorescent lamps or CCFLs) and light emitting diodes (LEDs). The sales name "LED TV" is really just an LCD TV which uses LEDs as the light source.

Among LED LCDs, there are two "styles" used to position the LEDs-edge lighting and direct lit. With edge lighting, LEDs are mounted on the edge and light is channeled behind the glass using guides to provide even distribution. This style allows for thinner profile TVs to be constructed. Direct-lit LED TVs position LEDs directly behind the glass, with each LED lighting up a set number of pixels grouped on the screen. This style allows for what is called local dimming, turning off individual LEDs to create greater contrast and better picture quality.

(Flat-screen TV - Via slashgear.com)

Plasma (Emissive Display)

Plasma technology works very differently than LCD. The display consists of two glass panels with a thin layer of pixels in-between. Each pixel has three gas-filled cells (sub-pixels-one for each color) coated with a phosphor(a substance that can exhibit fluorescence). When electric current is applied to individual cells, the gas (a noble gas mixture, usually xenon and neon) in the cells ionizes. Ionized gas (called plasma) emits high-frequency ultra-violet (UV) rays which cause the cell's phosphors to fluoresce, making them glow the intended color. Depending on which particular phosphor the cell is coated with, it will create a red, green, or blue glow. The ionized gas in a plasma TV involves the same mechanism as the fluorescent tubes and bulbs we see everyday, but on a much smaller scale.

Anatomy of the plasma cell.Via crutchfield.com

Plasma technology is referred to as an emissive display, because the light generated comes from inside the panel (inside the individual cells) as opposed to behind it.

Plasma vs. LED

Understanding how the technology works is one thing, but as a consumer the bigger question for me is: Which one is better? Unfortunately, in the TV world I found this to be a loaded question, since so much depends on one's definition of "better"and what that particular person is looking for. But figuring all that out for myself is a task for another day.

To be continued…

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#1

Re: TV Tech - Turning in the Tube (Part 1)

09/19/2013 10:06 AM

Just FYI, the LCD diagram shows an older style 'twisted nematic' liquid crystal cell. Nearly all TVs use a variation of the in-plane switching cell, which produces much better contrast and does not suffer the off-axis loss of contrast or loss of color saturation that the TN cells have.

Over the past 10 years LCD and plasma technologies have been pretty competitive in terms of visual performance, first one being better, then the other, back-and-forth. As LEDs continue to improve. LED-LCD TVs have gotten better. I prefer LED-LCD, but there are many who prefer plasma. For smaller HD-TVs, there hasn't been a choice, as it's been difficult to make plasma cells small enough to make a small TV. (You'll probably never see a cell phone that uses plasma.) I see more technological advancement going on in LED-LCDs, so I think plasma will eventually lose out.

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#2
In reply to #1

Re: TV Tech - Turning in the Tube (Part 1)

09/19/2013 9:11 PM

Well Oled is the current hot thing, but coming from a LCD background myself, i am always weary of new released Display technologies, they are released before all the bugs have been ironed out.

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#3

Re: TV Tech - Turning in the Tube (Part 1)

09/19/2013 11:37 PM

In my very limited experience, plasma TVs run significantly hotter than LED-LCDs. Heat is an enemy of many electronic components, so I suspect that the LED-LCDs will generally waste less energy and last longer.

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Re: TV Tech - Turning in the Tube (Part 1)

09/20/2013 1:21 AM

The heat in an LCD TV comes from the back-light as LCD is a passive system, well plasma and Oled create the light internally so there is where the heat comes from.

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