We’re a society that is joined at the hip to our technology: literally. With smartphones in holsters and ebook readers and tablets in our shoulder bags, we now take our digital connections with us wherever we go. But you may be in for a shock when you try to read your indispensable device when you’re out and about, wearing your favorite shades.
I made this discovery years ago, the hard way. Our sailboat has a GPS that doubles as a depth finder, and as we sail on the Chesapeake Bay, knowing how much water separates you from the bottom is essential information. I was making a tricky approach to a creek when I glanced down at the LCD screen to see what the depth was, and I saw a black screen. In a moment of panic, I thought the power had gone off on the device and I whipped off my sunglasses to start troubleshooting the problem. And the image on the screen magically reappeared.
What happened was that the polarization of the display and my sunglasses cancelled each other out. Polarizing films only transmits light waves that are oriented in a specific direction. This helps eliminate glare, and it creates a dimmer image because it blocks the light waves that are not in the correct orientation. You can witness this for yourself; look through two pairs of polarized sunglasses, and then rotate one until it is at right angles to the other. All the light should be blocked and you’ll just see black. (This is also a handy way to check to see if the lenses are really polarized.) You also can demonstrate the same effect using a pair of hair combs. When they are aligned so that their teeth line up, you can see through them. Rotate one to right angles, and your view will be blocked where they overlap.
So much for the science lesson; what does this mean in the real world? As I mentioned already, LCDs rely on polarized light to create their image. So it is possible that the light will not be correctly oriented to view when wearing polarized sunglasses. And that’s exactly what happens.
Take an Apple iPad and look at it in landscape mode while wearing a typical pair of polarized sunglasses, and the image will just look a little dimmer. Take that same table and turn it to portrait mode, however, and it goes black. You might think that OLED displays would not have this problem since they are emissive and do not rely on polarization to create the image, but some models like the Samsung Galaxy S actually go dark when held at a 45-degree angle because it uses a polarizing film to reduce internal reflections.
These observations were made by Raymond Soneira of DisplayMate, who also points out that there is a readily available solution for the manufacturers. They could use a “circular polarizer” — which is what is used in the 3D glasses at your local cinema — that will not block the image. Instead, there is a small color shift. According to Soneira, both the iPhone 4 and the Samsung Galaxy Tab 10.1 use this technology to eliminate the sunglasses problem.
So if you’re planning to catch up on some Netflix movies or other video on your next picnic, be sure to make a test run while wearing shades. You don’t want everything to go dark when you go outside.
Posted by Alfred Poor, April 24, 2012 6:00 AM
About Alfred PoorAlfred Poor is a well-known display industry expert, who writes the daily HDTV Almanac. He wrote for PC Magazine for more than 20 years, and now is focusing on the home entertainment and home networking markets.