Why Are Flat-Panel Screens Polarized At 45 Degrees?

[chilehed]

My job requires me to take a lot of data in automobiles, and since it's often very sunny I have polarized sunglasses.

I've had three of four different laptops at work and every one of them has the screen polarized at an angle, which is a pain in the rear because it means I have to tip either my head or the laptop.

 

Why don't they have them polarized vertically?

[alexander]

Well actually they have them polarized both ways, the basic layout of an LCD screen has a backlight, horizontally polarized film, lcd (sandwitched between 2 electrodes) and vertically polarized film (usually with a glass filter following both polarized films). The reason for this ofcourse is to control light, you have a polarized light entering the crystal matrix that depending on the state may change alter the polarization of the light, making the light pass or not pass through the second polarized film, that is how the intensity of the different colors is controlled to make up the image on the screen.

 

Ofcourse that is a very basic description of how an lcd works and there are a few types, but basically that is why the screen looks weird in polarized glasses.

 

Basically here is why polarized glasses don't work too well with LCD screens, polarized glasses work on the principal that a large flat, reflective surface (lake) produces a lot of horizontally polarized light, so the lens polarization is angled such that mostly only vertically-polarized light passes through. I am going to guess that your glasses are not actually polarized vertically, but rather at an angle. This is usually the case, because most people wear them inside and out, and especially in the car, where lcd screens are becoming more and more prevalent, and i am going to guess that not all of them use polarized filters in the order described above, to combat the fact that if they were vertically polarized, you would not be able to see anything on some lcds (if the outer polarizing filter was horizontal), the glasses are often polarized at a 45 degrees (as indicated by a little research) giving you some polarization, but also allowing you to at least somewhat see all lcds that you may encounter.

[CraigD]

My job requires me to take a lot of data in automobiles, and since it's often very sunny I have polarized sunglasses.

I've had three of four different laptops at work and every one of them has the screen polarized at an angle, which is a pain in the rear because it means I have to tip either my head or the laptop.

 

Why don't they have them polarized vertically?

Though I don’t have much hands-on experience with screen hardware, Alexander’s explanation of LED screen vs. sunglass polarization seems right-on to me, and suggests to me that the two will never play well together – though I’m some suspicious of this conclusion, as I think a lot of new aircraft have LCD screen instruments in their cockpits, and have never heard pilots complain about problems with polarized sunglasses.

 

In the near future – or now, if you’re willing to pay a lot for the latest and least mature tech on the market – you might be able to avoid the whole problem by getting a laptop with an OLED screen. AFAIK, OLED displays don’t polarize their output light at all, unless to avoid reflected light glare, which I think is done with an add-on filter.

 

Though large OLED screens are still rare and expensive, they’re common in some mobile phones, like the Samsung Galaxy S. If you can get around one of these with your glasses on (ie: you already own one, find a friend with one, or visit a phone store and play eager customer with the sales staff), I’d be curious to test and see if my guess is correct. I think I have some polarized movie glasses around, so will try this with my wife’s Galaxy X, if I can remember to.

[alexander]

Yes any technology that doesn't require a back-light would not really benefit from a polarizing filter, so yes any LED-based technology would be fishing-glasses safe :)

 

Actually craig, from flipping through a few airliner pilot forums the great majority don't use or just deal with using polarized glasses, especially in the aircraft with LCD screens, such as the a320, 777s and 747NG. The only real exceptions are good, high quality glasses such as the serengeti, they are not polarized at an obscure 45 degree angle so they work with most directly in front of you instruments, though pilots still say that when they need to look at something that is not quite directly in front they either have to tilt their head or look around the lens.