TVs 101: LCD/LED vs. OLED vs. PLASMA - AVS Forum
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post #1 of 3 Old 10-19-2012, 03:53 PM - Thread Starter
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So despite posting and lurking this forum for years, I'm still dont entirely understand all the tv tech thats out. The info about this on wikipedia and other sites is too convoluted, and even if its out there in a form I can understand, that info is too difficult to find. With this thread, I'm looking for some simple answers about how the three technologies in the title work.

I know how LCDs and LEDs are lit using either CCFL bulbs or LEDs which hit a liquid crystal piece of glass containing thousands of pixels which in turn creates the image. But further than that, how is the light from those bulbs separated to hit each crystal and create each color? Meaning, whats the distribution method from the light source to the the glass containing the pixels so that each pixel is lit with the right color?

Now with plasma, total guess here, but is it a glass screen containing pixels with the plasma substance within that layer of glass? A current is sent to specific zones/pixels making the plasma turn a specific color?

And lastly, OLED. I have no freaking idea what this is and how it differs from LED. I've asked before and was told its not self emissive like plasma, but much closer to how LEDs work. What exactly is the organic portion of this tech though, and how does it differ from the LEDs we have now?

Thanks, and I hope I get some informative answers.
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post #2 of 3 Old 10-19-2012, 06:58 PM
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I'll let others chime in about plasma, but let's start with LCD:
Quote:
Originally Posted by MaXPL View Post

So despite posting and lurking this forum for years, I'm still dont entirely understand all the tv tech thats out. The info about this on wikipedia and other sites is too convoluted, and even if its out there in a form I can understand, that info is too difficult to find. With this thread, I'm looking for some simple answers about how the three technologies in the title work.
I know how LCDs and LEDs are lit using either CCFL bulbs or LEDs which hit a liquid crystal piece of glass containing thousands of pixels which in turn creates the image. But further than that, how is the light from those bulbs separated to hit each crystal and create each color? Meaning, whats the distribution method from the light source to the the glass containing the pixels so that each pixel is lit with the right color?
For LCD's, simplifying it as much as possible:

Think of LCD like a stained glass window except it has millions of segments, millions of stained red, stained green, and stained blue elements. (over 6 million total for 1080p)
That's actually exactly what it is - filters in a precision-constructed "stained glass window array".
Put a magnifying glass close up to the screen, and you see the red, green, blue elements, usually in a grid array. iDuring video, you'll observe these elements brighten/darken individually.

Behind (or in front) of each filter, is black liquid crystals (same color as an old fashioned wrist watch) that selectively block light from going through. So where you saw a red pixel, is now a black pixel, etc. (and shades in between, of course). So, by simple additive light (red, green blue), the human vision blends that all into a full color view.

There's other layers, like polarizers, which are necessary for the liquid crystal operation and various tweaks to this technology improve contrast and angle of view and other things, but I'll leave that out of the equation for now. (Think of a cheap LCD wristwatch with a very 'faint' or 'nearly see-through' clock display -- poor polarizers, etc -- and a very good wristwatch with a very clear, dark, inky black clock display, very easy to read -- good polarizers, etc)

Now for the backlight.
In the strictly simplest sense, you can just shine a light behind a stained glass window.
Now you want something well-diffused (like the white fluorescent panels they use to hang up X-Ray films on at hospitals).
LCD backights used to be something like those, just a few horizontal fluorescent tubes behind a translucent plastic sheet, and the LCD glass went in front.
Heck, you could put LCD glass on a school overhead projector, and it works. (People still do this sometimes)
For these, there is no precision. You just light up the LCD panel as if it was a mere simple transparency. Lots of light is lost in computer monitors and HDTV's.
Of course, you can optimize by having highly directional light and focussed light (e.g. good reflectors, micromirrors, etc), so most of the backlight is wasted. Today's monitors have become much more efficient though, with LED's that focus light better, and better diffusers that lose less light to random scattering, etc.

lcdworks.jpg
From: How do LCD TV's work?

Thanks,
Mark Rejhon

www.BlurBusters.com

BlurBusters Blog -- Eliminating Motion Blur by 90%+ on LCD for games and computers

Rooting for upcoming low-persistence rolling-scan OLEDs too!

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post #3 of 3 Old 10-21-2012, 01:22 AM
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Quote:
Originally Posted by MaXPL View Post

And lastly, OLED. I have no freaking idea what this is and how it differs from LED. I've asked before and was told its not self emissive like plasma, but much closer to how LEDs work. What exactly is the organic portion of this tech though, and how does it differ from the LEDs we have now?

And more importantly I want to know if these Organic LED's are 100% Certified USDA Organic and Non-GMO !! ??? !!! eek.gifbiggrin.gif;) Or has Monsanto screwed up the LED business too ? tongue.gif
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