5
$\begingroup$

I've noticed that the reflection of a phone (or computer) screen in a window (or other smooth surface) has distorted colors (towards red-purple or green-yellow), which change as the screen is rotated

I thought it had something to do with LCD screens polarizing different colors of light at different angles. But some LCD screens polarize all colors in the same direction, and they have the same color changing reflection. Anybody have an explanation?

$\endgroup$
2
  • $\begingroup$ I think the polarization is the reason as well. If different colors are polarized slightly differently, the reflected image should have distorted colors, because intensity of light reflected from window depends on polarization. The question then is, why are different parts of display producing slightly different polarization. Similar but less noticeable effect is observable even if the light is not due to the phone but is merely reflected daylight. $\endgroup$ Apr 5, 2018 at 11:32
  • $\begingroup$ The polarization may be uneven because the screen is not perfectly flat, or because it experiences uneven mechanical stress. $\endgroup$ Apr 5, 2018 at 11:36

2 Answers 2

0
$\begingroup$

I noticed this too. My conclusion was that it's not because of the polarizers in the screen but the viewing angle. I am not sure about LCD screens but LEDs are focused in a direction and if you view it from a different direction, that particular color could now have lower intensity as compared to other colors in the vicinity and you'll different color. Or some internal component could be blocking the view of those particular crystals if viewed from a particular direction.

When you view a screen in a window, you are not viewing it from the front as intended but from an angle. This creates the color distortion.

$\endgroup$
1
  • $\begingroup$ That's an interesting and plausible theory. I haven't turned on my old phone that did this in a while and I'm not sure if it still works. I couldn't immediately reproduce the effect with my new phone (though I remember being able to do so in the past). I'm going to do a bit of tinkering and get back to you $\endgroup$
    – Shane
    Jan 4 at 9:34
0
$\begingroup$

You are possibly seeing the interference colors of a birefringent sheet in your phone screen. Many phone screens emit linear polarized light, but some phones have laminated glass on top of the screen containing a a polymer layer that is birefringent. A color pattern can be observed, because the polarization of a light ray is rotated by the birefringent layer and the amount of rotation is dependent on wavelength. Looking at the reflection of the phone screen in a window pane, at an angle of incidence of about 45°, is equivalent to looking through polarizing glasses at the screen.

enter image description here Purple and green colors in mirror image of phone in a window pane, as seen with with naked eye.

If you would like to test it on your phone, open an app that displays a white screen, and try to view the screen from very close to the screen, at a distance of just a few centimeters (the closer the better), while wearing polarizing glasses. As you already saw purple and green colors in a reflection of your phone screen, you will probably see an interference pattern like the photo below. It is characteristic for a biaxial birefringent layer. The colored fringes are called isochromes. The two bullseyes are the two axes of the birefringent layer.

enter image description here

Colorful bullseyes pattern, due to a biaxial birefringent layer in the screen of a laptop, seen through polarizing glasses from very nearby. Characteristic purple and green colors.

enter image description here The bullseyes pattern can be seen on many devices, like these 3 smartphones, 3 tablets and 3 laptops. Photos from a few years ago.

Some phone/tablet/laptop screens have the birefringent layer; others don't, like Iphones and Ipads. My experience is that whenever the reflection of the screen in a window has these purple and green colors, those colors can be seen even better through polarizing glasses. To see the complete pattern, with both bullseyes and the isochromes, the field of view must be more than 90 degrees. Therefore the best point of view is very close to the screen.

A related observation: take a laptop with a linearly polarised LCD screen. Cover a part of the screen with a "screen protector" (crystal clear laminated safety glass) for phones. When looking at the screen through polarizing glasses, the bullseye pattern appears on the screen protector, and not on the rest of the laptop screen.

enter image description here

$\endgroup$
3
  • $\begingroup$ I don't quite follow your answer. I don't see the bullseye pattern in the reflection. The reflection is monochromatic. Is this an important part of the explanation or simply an example of what birefringence sometimes looks like? $\endgroup$
    – Shane
    Jan 4 at 9:46
  • $\begingroup$ The images are actual photos of real phones and other devices. May be your new phone simply does not have the birefringent layer. What do you mean by a monochromatic reflection, do you not see purple and green anymore? (Edit: I moved some comments to the anwer) $\endgroup$
    – jkien
    Jan 5 at 0:05
  • $\begingroup$ By monochromatic, I mean appearing to be a single color. The screen light was reflected as 3 individual different colors, depending on the rotation of the screen. One of the colors was purple (forget the other two and the phone doesn't turn on anymore), which makes me think the color change was from the extinction of one of the 3 colors of light emitted by the screen (for example purple would be the result of green extinction). It showed the same effect viewed through polarized sunglasses $\endgroup$
    – Shane
    Jan 16 at 0:15

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.