Tuesday, March 26, 2013

Holographic LCD reflector

Over 20 years ago, Dupont developed a clever polymer that could be used to create holograms.  One promising application was a reflective backing for LCD displays.


While in theory any color could be created, green became the dominant color because the human eye is very sensitive to green, and because holograms are created by using high power lasers.  Argon lasers were the predominant high power lasers back then, and they are very good at producing green light at 514nm.  The hologram at right was made with a 514 argon laser.

The holographic reflector appears 6x brighter to the eye than does the traditional silver background.  This is because the hologram directs most of the light towards the viewer rather than distributing it widely like the silver diffuser.


It is easy to add the holographic reflector to any LCD.  This weather radio came with the usual dull gray background. I disassembled the radio and peeled the silver diffuser off the back of the LCD.  Then I attached the hologram to the LCD using a transparent adhesive film.

Here is a Fluke multimeter that I modified, next to an unmodified one. The contrast between the modified and original radios was even greater.



Unfortunately, the idea never caught on.  Casio used it in some digital watches like this one, but I know of few other commercial applications.

Update:  A reader has supplied the following additional information:

Found your post on the DuPont holographic films. Nice descriptions and details. I was quite involved in the project. A correction if I may, the brightness enhancement films did catch on in a big way! Almost all of the Timex watches for 3-4 years, almost all of the higher end Motorola cell phones for 3-4 years, and many other applications. What ended the growth was the introduction of full color LCD's.
Doug




The diagram at left illustrates how this works.
Unlike a normal mirror which reflects light away at the same angle it is received, holograms can be designed to reflect light at any angle.  This property can be used to great advantage by reflecting ambient light at a different angle than the glare reflecting off the surface of the LCD display.
In the diagram, the glare from overhead light is reflected down, away from the viewer, while the green light from the hologram is directed towards the viewer. The result is the brilliant, high contrast display shown above.



 I have a few square feet of the stuff, and convert most  of my LCD displays.

Like most holograms, this hologram is a picture of something.  In this case, it is a picture of a ground glass plate illuminated by 2 laser beams from the same laser.  The hologram reflects light at the same angle that the laser beams were at when they illuminated the glass plate.  We would then make a master hologram from which copies could be made.
At right is a sheet of copies.  This picture was taken in a brightly lit room, but the holograms were so bright that the room appears dark.  one neat attribute of holograms is that they are nearly transparent.  Here is the exact same sheet when looking through it at the overhead lights that previously made it glow bright green. 











We tried other colors with limited success.  Here is a blue one.  Not nearly as effective as the green. The bright objects in the background easily wash out the weaker blue.




By combining red, green and blue lasers, we made some white ones.  However, even those did not perform as well as straight green, which can be seen shining  through the white one.








Finally, here is a picture of some scraps.  They only glow when viewed from the proper angle.  The ones that appear dark are pointed the wrong way.

 Years ago, someone had the idea of chopping these up and putting them into paint.  A good idea, for unlike dyes, holograms never fade.  Unfortunately I don't believe the inventor got very far with his idea.


One idea that DuPont and some automakers invested a lot of time in was a holographic center stoplight, or CHMSL, as it is known in the industry.  The idea was that a hologram in the rear window would glow red when the brakes were applied, but otherwise would be transparent.  While it worked, it had no real advantages over traditional stop lights.
Another, better idea was a transparent television set.  When not used, it appeared to be a somewhat foggy, but generally clear, window.  When turned on, the picture was quite good.  One idea was to use it to display advertisements in store windows, then let people also see inside.  Unfortunately I have seen little of that idea since then.

12 comments:

  1. Love the hologram 'backlight' idea, What would you recommend for a purchased sheet to do some conversions or sampling.

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  2. Really like the "backlight" idea using holographic film. Where can this stuff be purchased ? Thanks

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  3. Unfortunately, I don't know. I left Dupont over 12 years ago, and then Dupont consolidated everything in a subsidiary in Utah that I believe was called Krystal Holographics back then. I have no current information on the company or their products.

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  4. Robert
    Found your post on the DuPont holographic films. Nice descriptions and details. I was quite involved in the project. A correction if I may, the brightness enhancement films did catch on in a big way! Almost all of the Timex watches for 3-4 years, almost all of the higher end Motorola cell phones for 3-4 years, and many other applications. What ended the growth was the introduction of full color LCD's.
    Doug

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  5. Doug,
    Thanks for the info!
    Regards,
    Robert

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  6. Hi Robert, I'm trying to fix an old lcd screen but the silver reflector film seems to be discoloured. Do you know where I could buy these silver reflectors? Thanks in advance!

    Daniel
    Singapore

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  7. Sorry, I don't know where to buy them. Perhaps you can disassemble another display for the reflector?

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  8. Thanks Robert. In your post you mentioned that you peeled off the silver reflector and put on the holographic one, are you aware whether there is a polariser in front of the silver reflector? I see that your LCD appears a bit faint under the holographic one, thanks.

    Daniel

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    Replies
    1. The polarizer is still there. I believe some of the segments look faint because the camera captured some of them partially turned on. Like most displays, the segments in this one are time-shared in order to reduce the complexity of the wiring. This goes unnoticed by the human eye, but is easily captured by a fast camera.

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  9. I found a 20 year old timex ironman (721) watch in my attic that has this film. I never thought much about how it worked but was intrigued by it. What I noticed was that in areas of diffuse light (eg indoors) it is a big help, when the light is already more or less collimated (outdoors on a sunny day) it is not. This makes sense now. If the hologram takes light from many directions and scatters in one direction, then the reverse must be true: if light arrives from one direction it will be scattered diffusely. This is an interesting design tradeoff - degrade the display quality slightly when used outdoors for a big improvement indoors.
    BTW - its a shame they don't make this anymore. This is the best simple cheap running watch I have found.

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  10. Hello, I've been looking for information about something similar for a long time, but instead of using the regular reflector or holograms I'm wondering how would light reflective paint (such as the one seen in street lines) would look like.

    I think this would be great in many cases (maybe not for all watch models of course and this is mainly for digital wristwatches), because the regular reflectors always kind of work great in some situations and then bad in other situations (like sun vs shadow or different angles). I think reflective paint would be great for normal light conditions and certain illumination scenarios. Manufacturers could advertise it like a safety feature (for example when walking in a street at night).

    Unfortunately I have no tools or materials to try this. So maybe someone is interested in doing it and posting the results? The paint would have to be a fine grain reflective white paint (for testing purposes), it could be applied to a paper and then placed behind the lcd display.

    I had the idea and tought I could profit one day :) but I really think I have no chance of doing it so I'm posting it to the public.

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  11. Hello,
    I reached your site looking for Silver Reflector...
    I am interested in your "holographic reflector". Is tI reached your site looking for Silver Reflector.
    I am interested in your "holographic reflector". Is this reflector commercially available? I think that I want this item...
    Best regard

    ReplyDelete