> You could just rip the film out of an old LCD screen and rotate it 90 degrees. At first, I also thought this was just a linearly polarized filter rotated ort

> You could just rip the film out of an old LCD screen and rotate it 90 degrees. At first, I also thought this was just a linearly polarized filter rotated orthogonal to the polarized emission of (typical) LCD panels, which would be far from new. However, that doesn't explain how the film would block an LED billboard which are unpolarized. The article isn't clear if their talking about LED billboards or LED backlit panels, the latter are still essentially LCD panels and thus must be polarized. If the latter, then I agree with you this is as far from revolutionary as you can get. The article does say that the film selectively filters out wavelengths of light, rather than selective polarization. So, what I assume the film is actually doing is playing off the fact that display manufactuers strive for saturated color emission from the RGB subpixels. The film is a "notch filter" with three stopping bands (in the red, green, and blue) portions of the visible spectrum. Pixels don't emit single wavelengths (e.g. 555 nm for green). If they did, that would imply pure saturation. Lasers are virtually purely saturated, but even then they generally a band (ableit extremely narrow) of wavelengths. Display pixels, even highly saturated emit in a band. However, LCD's and the typical high quality inorganic LED's used in billboards emit relatively saturated ligh (e.g. ~30-50nm wide bands), and are able to do so largely with the help of dye-based absorbing band-pass filters (basically the opposite of notch filters) that only allow a few wanelengths to pass through while others are absorbed and radiated as heat. OLEDs on the other hand emit specific wavelengths of light and therefore do not need/use color filters. However, OLEDs also have inherently wide emission spectra (perhaps ~100nm) due to the fact that it is difficult to finely tune the exciton (excited particles that emit light in OLEDs) energy levels to produce highly saturated emission. Interestingly, Quantim Dot LEDs that function similar to OLEDs, are more saturated that OLEDs because it's easier to control the size of quantum dots which directly relates to emitted wavelength, alas, these LEDs are typically only used in LCD backlights (I'm not sure why). The point of all this is that you could easily design an optical film with 3 R, G, and B notches of ~50nm or so, which would block almost all light from any display with saturated pixel emission. However, less saturated OLED light would still bleed through. You can't really widen the notch filter bands too much because then you start blocking every band in the visible spactrum, meaning less ambient light can pass through, until ultimately you can't see through the film at all. Anyhoo, that's why I suspect this is notch filter film vice polarized filter.