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Does anyone know if there is a component or a solution for creating a switchable polarizing film using DC-power? (i.e. a film/glass/substrate/etc that can be switched between a polarizing and a non-polarizing state).

Since this functionality is included in every LCD-screen, I think it has to be possible. The closest solution I can find is smart glass, but they require AC according to my understanding

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While you can polarize an LCD screen with a DC voltage, if you do not switch polarity of the drive rapidly, you will plate the surface. This kills the LCD. So a polarizing film would normally have to be driven with an AC signal, typically a square wave.

This could be as easy as using DC to power a fixed oscillator. For a normal LCD.

You might want to look at a Boogie Board. This is a physically changeable LCD with a click reset of crystal. It is essentially a single LCD pixel. That company makes an LCD bi-stable display. It is similar to e-ink, but with LCD technology. We visited the factor for these in Shenzhen late last year. They can change pixels then let the hold. While I don't know if this is DC driven, it is the closes thing to what you are looking for that I have seen.

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What makes you think that LCDs use DC? DC is bad for liquid crystals- it causes electrolytic action. It's not that it doesn't work, it does, but it will eventually destroy the screen. LCD screens generally have drivers and such on board which generate the complex AC waveforms required for a multiplexed LCD display. A single on/off would only require a panel and some source of AC. For an example of this, see self-darkening welding goggles.

If you want something that works on DC (one polarity for light, swap polarity for dark), you can consider electrochromic technology. For example, http://sageglass.com/technology/faqs/

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