Why not LED?

Discussion in 'Displays' started by Jackson L, Dec 8, 2004.

  1. Jackson L

    Jackson L Stunt Coordinator

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    I'm sure there is a good reason that there aren't any LED TV's out there but I'm wondering why that is. LED's are very cheap, respond instantly, last a very long time, they are bright, and they can be made very small. Why not make a TV in which each pixel is made of three LED lights (Red, Blue, Green)? It doesn't seem like rocket science to me. Those giant screens in sports stadiums and Times Square use LED's so why not apply that to a TV? Maybe I'm completely out of touch. Maybe this has already been done or is soon to be released. I have seen a Sony TV that uses LED's as a backlight but wouldn't it be cheaper to use LED's as the pixels? Does anyone know anything about it?
     
  2. ChrisWiggles

    ChrisWiggles Producer

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    Probably because LEDs are still large.

    LED TVs exist, and they are in stadiums, and they're huge.
     
  3. Leo Kerr

    Leo Kerr Screenwriter

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    The finest resolution LED screens I've seen - not using OLEDs - is a 6mm dot pitch.

    Thats on the Barco i6 series screen.

    The image starts forming at about ten feet (when you stop seeing pixels and start seeing picture) but you really need to be 20 feet away or more.

    They have an unbelievable contrast ratio and brightness (full-sunlight visible) and look amazingly good - from 20' or more.

    They do have some drawbacks, though.

    1. Heat (limits the minimum size of the pixels.)
    2. Heat (you can feel a full white screen at 20'.)
    3. Power (each 18" square panel uses something like 240W)
    4. Power (you can feel a full white screen at 20'.)
    5. Mass (each 18" square panel weighs about 50#, not counting the chasis and framing to link to other panels.)
    6. Cost (enough said)
    7. Noise (they have fans in them, too.)

    On the other hand, if you're rich, you can build one **** of a drive-in theater with them. Fed from HD, it should look really fantastic.

    (Note, I don't recall how they handle low-level signals... some of the cheaper ones have a shimmer that's really annoying.)

    Leo Kerr
     
  4. MikeHerbst

    MikeHerbst Stunt Coordinator

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    The other thing is the relative brightness that can be acheived by each color. The process to make red, green, and blue LEDs results in different brightness levels. Brightness from a red LED is very easy. Brightness from green, is tougher, but doable. Brightness from Blue is still technically a tricky thing to do efficiently. (i.e. where you don't pump so much current you're eroding the substrate in the semiconductor).

    Each "pixel" of the Stadium-sized LED screens is actually made up of FOUR leds. One Red (at half Power), One Green (at full Power), and TWO Blues (at full Power) are needed to get the brightness levels to match.
     
  5. Leo Kerr

    Leo Kerr Screenwriter

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    ...that's with the 'Lighthouse' and other makes... the Barcos are using different dies and are just using three diodes.

    Actually, it's very easy to get a very high-brightness blue led (standard white LEDs are blue LEDs with a phosphore that captures some blue and re-emits white.)

    The catch with blue LEDs is that they typically run a 3.6volts, while red and greens run at 1.2 or 1.5volts.

    Leo
     

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