Dielectric Mirror Shines Bright

We knew the mirrors in our house were not really very good mirrors, optically speaking. Your mirror eats up 20 to 40 percent of the light that hits it. High-quality first-surface mirrors are better, but [Action Lab] has a video (see below) of something really different: a polymer dielectric mirror with 99.5% reflectivity. In addition, it has no Brewster angle — light that hits it from any angle will reflect.

Turns out something that thin and reflective can be hard to find. It also makes a little flashlight if you roll a tube of the material and pinch the back end together. The light that would have exited the rear of the tube now bounces around until it exits from the front, making it noticeably bright. The film comes from 3M, and apparently, they were surprised about the optical properties, too.

Paradoxically, the mirror is made of several layers of transparent film. The video explains how a bunch of transparent layers can reflect light.

Material like this help spread light behind cell phone screens. Efficiency is important because everyone wants longer battery life with their phones. We aren’t sure what we want to do with this, but it must be something. Our guess is since the reflections take place in different layers of the polymer, it wouldn’t make a good telescope, but we could be wrong. The tape isn’t dirt cheap, but it doesn’t seem outrageously priced if you can find it.

It might make a good surface for your next James Webb model. We wonder how it would work in a laser projector?

31 thoughts on “Dielectric Mirror Shines Bright

  1. So if almost perfectly reflective… That implies that it could make a good insulator, or keep things cool if all the ‘heat’ is reflected away? At any rate it appears to be a really neat matter that should have a lot of applications.

    1. matter … material …. To bad ya can’t edit :) . One other thing… If you pinch the top the tube off real fast, is the light photons/waves ‘trapped’ :) and just bouncing around in the tube looking for a way out?

      1. Well,doing the math, it is 99.5 reflective so it is absorbing .5 percent of the photons on each bounce. At the speed of light in that small a volume, it would all absorb pretty quickly. So no, it is not an effective bag of light.

        1. A good application might be mirrors for focusing solar energy onto photoelectric cells allowing for more usage of the expensive cell. Main issue would be heat management at the reflector and on the cell itself. Possibly also useful to redirect sunlight for household lighting.

        1. The material is made by layering alternative high and low refractive index transparent polymers with thickness tuned so that reflections constructively interfere.

          I.e. most likely it works pretty well for near IR and unless the polymers are particularly opaque to IR you probably have decent scope to optimize for wavelength.

    2. It’d make a good radiant barrier, as often installed directly under a roof.

      It wouldn’t function as the insulation that typically goes on the attic floor.

      It’s probably an excellent conductor of heat, though – as materials tend to be one or the other

    1. More 9s at a specific wavelength, right?, and I bet transparent at others – there’s that tuning of the layers again. It’s cool stuff.

      3M makes lots of fun films for LCD construction, including prismatic and one of my personal favorites, a film that’s fairly reflective except at one polarization, where it’s transparent. All of these small optimizations add up when you’re building LCD backlights, and lead to less heat and more battery life for a given brightness.

      Another fun property of a non-metallic optical mirror? It doesn’t block radio.

  2. So I guess if youtubers do those long ads n their video that YT does actually get a cut from the advertiser? Just like they do with inserted separate ads.
    Except now its harder to block, which makes this kind of advertising actually pretty hostile.

  3. Howdy, One sight of Dielectric Mirror and a sign lit up in my head that said Hidden Television!

    Dielectric mirror films or sheets are (claimed to be) used to make what looks like a TV when it is on and displaying a picture, or like a wall mirror when the TV is off. In fact there’s a company called Hidden Television that custom builds hidden televisions that use a (supposed) dielectric mirror, or they sell just the dielectric mirrors alone if you want to DIY your own Hidden Television.

    I read all the stuff on the Hidden Television web site including the free downloadable specification .pdf file. Although the mirror is called “Dielectric”; I have doubts about that. It looks to me the mirror they use is made by coating a thin sheet of flat float-glass with some standard reflective material. According to the downloaded .pdf specification file, the mirror has 25% transmittance and 71% reflectance. I think a real dielectic mirror would have much better specifications, especially in the reflectance number. Yeah just remember, this is the Internet – Mmmkay ;-)

    Note: I am the O.P. of this comment on Hackaday. I have zero affiliation with Hidden Television.

    From the Hidden Television web site: “Did you know? For over 15 years, Hidden Television has been the only mirror TV company to offer guaranteed quality. We work with you to order the perfect TV, and back up our craftsmanship with returns and exchanges. We make shopping for a mirror TV fast & easy!”

    Check it out for yourself: https://www.hiddentelevision.com/

    And of-course the obligatory video is here:



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