Do *all* LCD TVs have a Fresnel Foil? (even big or HDR TVs?)

Discussion in 'General Electronics Chat' started by hoholger, Sep 13, 2019.

  1. hoholger

    Thread Starter New Member

    Sep 13, 2019
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    Hi all,

    I am fascinated by the project of turning TVs into "Realistic Artificial Daylight"
    https://www.youtube.com/watch?v=8JrqH2oOTK4
    They use old LCD TVs with a Fresnel lens to create parallel light, which apparently gives off the effect of very realistic daylight.

    I might be able to get a broken 65 inch LCD TV from a friend (panel glass seems ok).
    But before I take all the effort of transportation and disassembly, I wanted to double-check: do all LCD TVs contain the Fresnel lens? The guy in the video says that very old or very big might not.

    The TV is quite big with 65 inches, and it also has an "HDR" feature, which - as I understand - means it must have bright background lighting.
    I'm wondering if it still has the LED backlight from the side of the frame, or if it might have lots of LED strips on the back - but might leave out the Fresnel lens, and would be unsuitable for the project.

    Any insights are highly appreciated.

    Thanks,
    Holger
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Why does it need to be "parallel light"? :confused:
    Your eye doesn't know the difference. :)
     
  3. Externet

    AAC Fanatic!

    Nov 29, 2005
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  4. SLK001

    Senior Member

    Nov 29, 2011
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    LCD TVs have polarizing films on their surfaces (all LCD displays have them), not Fresnel lenses.

    If you're looking for a Fresnel lens, look on Craigslist for a projection TV. You can even go so far as to put your own ad saying that you will pick up someone's projection TV for reuse. You can't sell a projection TV, so anyone who has one will simply either give it away or put it to the curb. I've gutted a few of them for the electronics, the speakers and the plexiglass sheets, plus I also took the Fresnel lens, but I haven't figured out any use for it other than just use it as a plastic sheet.
     
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  5. hoholger

    Thread Starter New Member

    Sep 13, 2019
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    The guy called this layer here a Fresnel layer. It definitely does distort.

    [​IMG]
    Here's the position in the video when he mentions it in the video and dissects the different layers:


    Is this not a Fresnel lens? Does anybody know what it really is then?


    The guy in the video says that the light drop off is much reduced. The more parallel light is associated with daylight by the brain.

    With a lens:
    [​IMG]
    without a lens:
    [​IMG]
     
    Last edited: Sep 14, 2019
  6. DNA Robotics

    Active Member

    Jun 13, 2014
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    The Fresnel lens is behind the LCD panel to make the back light a general glow. Yours probably has one. I say go for it.
     
  7. Externet

    AAC Fanatic!

    Nov 29, 2005
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    That layer behind a LCD panel is not a Fresnel lens. It is a diffuser, to avoid seeing the LED emission points, is made of white translucent plastic, not transparent. Projection TVs are at curbs and at my neighborhood Salvation Army stores for usually $5
    Other clear films in LCD televisions are polarizing filters.
    Another horrible video from a 'youtuber' ---->
     
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  8. SLK001

    Senior Member

    Nov 29, 2011
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    +1 on what @Externet has said. That layer is a DIFFUSER layer. It diffuses the LED or CCFL light so that you can't see them thru the TV screen. Your video person doesn't even know what CCFL means.
     
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  9. narkeleptk

    Member

    Mar 11, 2019
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    Well, you know he's on youtube so he must be an expert!
     
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  10. hoholger

    Thread Starter New Member

    Sep 13, 2019
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    Thanks guys for your quick answers. :)
    Makes a lot of sense, actually. A Fresnel lens would only make sense for a point light (like a rear projector - as many mentioned) in focal distance, not for a diffusely lit light source within a distance of <0.1 inches or a few millimeters.

    Thanks to your hints, with the right buzz words, I found some information on google.
    Could the film that he shows above be a prism sheet or BEF (Brightness Enhancement Film)?
    And because it has tons of small prisms, he mistook it for a Fresnel lens.

    [​IMG]


    Using one of these BEF or prism sheets would still have the effect he mentions, though, wouldn't it?
    That means, the light is focussed on a smaller viewing angle, therefore giving the illusion of parallel (sun) light.
     
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