Maybe this is more of an Electrical Engineering question, but does anyone know why iPhones looking green/red through a linear polarizer? I find it strange that the light coming out would be polarized... I mean I guess there's no reason it shouldn't be, but what is making it polarized, moreover, what goal does it serve?
1 Answer
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The key idea of how LCDs work is that a peculiar substance, a "liquid crystal", is placed between two linear polarizer filters. The filters are crossed, so normally a backlight behind the LCD isn't seen, appearing black.
When voltage is applied to part of the device, such as one segment of a 7-segment digit, or one row and column defining one pixel in an iPhone display, the liquid crystal twists the light polarized by the back filter, allowing it to shine through the front filter.
With color filters to make RGB images, imperfect polarization depending on wavelength, and interference effects due to reflections between thin optical layers, it's no surprise you'd see shimmering colors and murky darkness or other optical weirdness when viewing the device through a linear polarizer. Optical engineers balance different imperfections in ways to cancel out or at least to appear not imperfect. The display is, of course, designed to look good to normal human eyes without polarizers.
See an explanation and illustration at http://electronics.howstuffworks.com/lcd2.htm or at http://lcp.elis.ugent.be/tutorials/lc/lc3 or at http://www.dciincorporated.com/products/overview.html or google for words like "LCD polarized construction", "how liquid crystal display works", "physics LCD display optics", etc.
