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

Thread Starter

hoholger

Joined Sep 13, 2019
3
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
 

SLK001

Joined Nov 29, 2011
1,548
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.
 

Thread Starter

hoholger

Joined Sep 13, 2019
3
No LCD televisions have Fresnel lenses.
Only projection televisions do.

View attachment 186122

I removed the lens and used it for burning and melting mounted on a pivoting frame. It is brutal at full sunlight.

----> https://www.geek.com/news/fresnel-l...on-tv-used-to-create-solar-death-ray-1610860/
The guy called this layer here a Fresnel layer. It definitely does distort.


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?


Why does it need to be "parallel light"? :confused:
Your eye doesn't know the difference. :)
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:

without a lens:
 
Last edited:

Externet

Joined Nov 29, 2005
1,846
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' ---->
 

Thread Starter

hoholger

Joined Sep 13, 2019
3
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.




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.
 

doofus434

Joined Jan 3, 2021
1
Interesting that lots of people in this thread that will pan a youtuber for making an innocent video and not knowing a few things while incorrectly mislabeling something as a "diffuser sheet". The polarizer films are on the front of the LCD. @Externet @SLK001

Diffusers in LCD backlights are the the microdot plates. The sheet that the OP is describing that distorts light is a brightness enhancement film that is using internal reflection to make sure that the light that gets sent to the LCD is the right angle and polarity.
 
No LCD televisions have Fresnel lenses.
Only projection televisions do.

View attachment 186122

I removed the lens and used it for burning and melting mounted on a pivoting frame. It is brutal at full sunlight.

----> https://www.geek.com/news/fresnel-l...on-tv-used-to-create-solar-death-ray-1610860/
That is simply not true. Most/?All edge lit LCD TV's monitors etc have fresnel lens'. Where did you get this idea? The lens is part of the light diffusion system.
 

chris_22

Joined Nov 5, 2021
3
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.




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.

Did you build it? I'm also interested in building this light.. What type of sheets did you use for diffusing light?
 

dl324

Joined Mar 30, 2015
14,458
Interesting that lots of people in this thread that will pan a youtuber for making an innocent video and not knowing a few things while incorrectly mislabeling something as a "diffuser sheet". The polarizer films are on the front of the LCD. @Externet @SLK001
There are a lot of idiotic videos on YouTube. The material isn't peer reviewed so anyone can try to act like they know what they're talking about.
 
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