Trick Google Used Hides Secret Messages On LCD Screens

[Travis] didn’t get picked to go to Google I/O this year, but he did have some I/O inspired fun after the fact. His friends who did go told him about specially modified LCD screens Google had scattered around the event. The screens showed normal show information when viewed with the naked eye. When viewed through a special transparent badge included with the I/O swag though, a URL for Google’s scavenger hunt would magically appear. [Travis] was intrigued by the effect, and became hell-bent on reproducing it himself.

[dual-lcd-3Travis] figured out the transparent badge was actually a polarizing filter. Every standard LCD has two of them, usually bonded to the glass of the LCD itself. If you remove the filters from a LCD, you’ll get a prime view of the backlight – unless you’re wearing polarizing glasses of course. Google’s monitors didn’t have that effect though. They showed a full color display, with a second full color hidden display only visible through the polarizer. [Travis] is intelligent and experienced, so it only took a bit of three-dimensional thinking for him to figure out Google’s trick. There are actually two LCDs used in the display. The first is a standard LCD with backlight. The trick is to strip the polarizing film off a second LCD and place it in front of the first. The second LCD will be invisible to anyone – without the polarizer.

[Travis] quickly set about replicating the display using several obsolete VGA LCDs. He quickly found that the hard part was peeling the polarizing plastic from the thin glass LCD sandwich. Several LCDs gave up their lives in the effort, but in the end [Travis] was successful. He made everything fit in one case by using a thin LED backlight in a case designed for a monitor with a Cold Cathode Fluorescent Lamp (CCFL).  The result looks exactly like a standard LCD – that is, until viewed through a polarizing filter. Click past the break to see the hidden message LCD in action!

37 thoughts on “Trick Google Used Hides Secret Messages On LCD Screens

          1. Yes indeed, I asked this question and got a blunt answer lol. I expect that one image has to be either the image presented to the viewer with the polarising filter or the image presented to the viewer with no filtering. In each case I expect that the image sent top the LCD screen would have to be the difference between the two images.

          2. Actually… Remove polarisers from two LCDs, turn one through 90 degrees, then try it. You’ll get colour from one display, then if you rotate the polariser you’ll get it from the other display. Make glasses with one polarisation for each eye.
            Of course, you have to line your eyes up carefully or you get crosstalk. Commercial systems use circular polarisation, so that the panels are always 90 degrees of, even if you got your head.

    1. There actually is/was a 3D display that worked exactly like this.

      iZ3D’s monitors a pair of stacked LCDs, with the second only visible while wearing the polarizing glasses. I actually have one of the monitors (though it died some time ago) and, TBH, the effect was very meh. I don’t know if it was because they were cheaply made or it’s just an inherent issue with the method, but there were ghosting and brightness issues aplenty. Novelty of it wore off quick thanks to that.

      Shutter glasses work much better, as do the screens with special lensing on them that don’t require glasses at all.

      1. Shutter glasses make the picture way too dark. But there are 3D TVs e.g. from Phillips, which work with passive polarizing glasses with very good effect. I am sure they do not use a stacked LCD approach but have probably a polarizer in it which alternates every second line or pixel column.

    1. How dare you. Google is doing a lot more for the world than your fat ass. You pay for the free services that you use by letting them mine your information. It’s absolutely a fair trade and it’s not one that you can’t say no to. Stop use by Google’s services.

  1. As a kid I used to do this with dollar-store calculators and watches. If you can successfully peel off the front polarizer and the reflector from the back polarizer, you get a “window” with the same effect.

  2. I must have missed something here! How is this working. I get the idea of removing a polariser from *one* screen and then putting polarising film on some glasses but I don’t get why *two* screens are used and how you can get two images.

    1. One screen is normal. You see the image from it just fine, no problems. That normal screen is the *backlight* for the “trick” screen.

      The normal way to do this trick is to have just the trick screen and the backlight. No polarization = see backlight only. Polarization = see trick screen.

      This way no polarization = see *normal* screen only. Polarization = see trick screen.

    1. Would not work. The LCD needs two polarizers to work – or a polarized backlight and the polarized glass to view. The rear LCD works as a polarized backlight. If you want to use an OLED then the LCD needs it’s rear polarizer for the trick to work.

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