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I can't find any information about this on Google, so I thought I'd ask it here.

I am looking for a LCD Screen-like panel which uses a mirror-like liquid crystal so that I can make a pane of glass into a mirror electronically.

The "pixels" do not have to be as small as a normal LCD display, in my case I want "bands" of pixels that have a dimension of 30x2 centimeter.

So it's not really a display, it's more like a dynamic mirror.

Does this technology exist? I remember seeing something like this a couple of years ago but I can't remember where.

For my prototype I'd have a big glass panel resembling a window, and using for example an Arduino I'd like to switch some segments of the panel on or off, and those segment will reflect light with a mirror-grade finish.

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  • $\begingroup$ A standard LCD can do this. The question is; what do you want the pixels which are turned 'off' (not reflecting) to look like? A standard LCD will make them dark. $\endgroup$
    – Chris Mueller
    Nov 8, 2015 at 18:44
  • $\begingroup$ No no, I need "pixels" that reflect light, not block light. When the "pixel" is "OFF" they simply become transparent. So either a pixel becomes a mirror or it becomes invisible. Imagine the effect of filling the pixels of an LCD panel with mercury and controlling each pixel. Imagine that effect. Now of course mercury would not be the proper material for this application, but it's an illustration. I need to know if there is any material that is reflective like a mirror and also electronically controllable. $\endgroup$
    – vaid
    Nov 8, 2015 at 21:43
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    $\begingroup$ It can be done for individual wavelengths, but I don't think there are any reasonably mature technologies that can do it for the whole visible spectrum. $\endgroup$
    – Chris Mueller
    Nov 8, 2015 at 23:03
  • $\begingroup$ I'd be happy with RGB reflection if that's all that is needed to give a mirror-like effect. Humans are going to be able to see themselves in the mirror-display just like a normal mirror, so if Red Green Blue reflection is sufficient then that's OK. Do you have any links or any info on what I can Google to find what I need? $\endgroup$
    – vaid
    Nov 9, 2015 at 8:04
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    $\begingroup$ The way I'm thinking of to do it for individual wavelengths is with some type of piezo-electrically controlled Fabry-Perot cavities. There is no mature product which works this way that I'm aware of. I think the answer to your question, unfortunately, is no. $\endgroup$
    – Chris Mueller
    Nov 9, 2015 at 15:27

3 Answers 3

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If you are looking for an individually-addressable mirror array, a Digital Micromirror Device (DMD) is what you are looking for. It is used to adjust the brightness of pixels inside a DLP projector by adjusting how much light is display per pixel via pulse-width modulation. By adjusting how fast the mirrors reflect from on to off, the pixels can be adjusted for brightness. The downside is that these are generally very small devices do to their application.

If you're simply looking for a way to turn a clear pane of glass into a mirror, 'Smart Glass' may be what you're looking for. Electrochromic panels allow you to pass a current through them to adjust opacity, but not reflectance.

Please edit your comment to reflect (see what I did there?) your intended application and we can further help you identify the component/material you are looking for.

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  • $\begingroup$ DMDs won't work for two reasons. First, they aren't clear. Second, they are very small being chip level devices. $\endgroup$
    – Eric S
    Aug 2, 2017 at 14:47
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The closest thing I can think of to this would be a digital micromirror device, like the kind that are used in digital light projectors. See the video here, explanation of operation is about 2:10 in the video. I don't think you're going to find an LCD mirror that's see-through when not in use (the application I think you're asking for), but I could be wrong.

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  • $\begingroup$ DMDs won't work for two reasons. First, they aren't clear. Second, they are very small being chip level devices. $\endgroup$
    – Eric S
    Aug 2, 2017 at 14:47
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As a materials person, one approach would be a material that can change phases with electronic stimuli such that one phase has no electronic band gap (a conductor) and the other phase has a band gap in the visible range (a semi-conductor). I am unaware of and such material, and should such a material exist it would probably be seeing extensive use in Dubai and Las Vegas if it were economical. The biggest challenge in designing such a material for production is ensuring the phase change material is perfectly flat as though polished in the reflective state, and not too rough in the transparent state, e.g. to have a negligible volume change associated with the phase change.

The closest existing materials I am aware of do not have image reflection, but instead become opaque, and there have been several approaches, including suspended particle, electrochromic, etc (see the link). Such a material does what I've explained except instead of changing band-gaps with phase, simply causes changing organization of ionized or ionizable materials. The issue with modifying this to become reflective instead of merely opaque is again related to roughness. The material must reflect nearly all of the incident light, and must do so with a smooth, as-if-polished surface.

The way most LCDs work is by electrically activated, nematic (threadlike) liquid phase crystals which twist into and out plane with the panel, blocking light as required. None of the material properties change as a result of the process, so the LCD crystals would need to be always reflective, which might create an unusual and distracting appearance when the pixels are "off", though it would act nicely as a mirror when on. How to create a reflective nematic liquid-phase crystal is an interesting question in itself. Additionally, to have a polished mirror effect, the crystals would need to line up perfectly, or the image would be distorted in a distracting way. As it stands with displays, if the crystals are a bit unaligned the display still colors the light passing through effectively.

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