How do anti-glare phone covers work?
Listener Joe got in touch to ask, "When it’s sunny it’s hard to make out what’s on my phone screen, even when it’s on the highest brightness setting. There are anti glare phone covers, how do they work?"
Nanomaterials expert Jess Wade from Imperial College London is here to explain how the materials in your electronic devices make everyday life easier...
Jess - Yeah, this is actually a perfect question for me, because these are the kinds of materials that I research. The reason that you want an anti-glare phone cover is because when you're outside on a sunny day, like Joe is, even if you turn your brightness up really high, the light from behind you, so the sunlight, or if you're at home just light around you, goes through all of the different layers of your mobile phone; your screen, the optics, the thing that's emitting the light, and it gets to something at the back. And that thing at the back is usually an electrode. It's somewhere that we inject the charges, but crucially it's made of metal. So it's shiny. So what your sunlight behind you does is hits off that shiny layer at the back and interrupts the image that you're trying to look at, or the text message that you're trying to read. So what these anti-glare filters do, as Joe suggests, they're quite sophisticated optical components, and they basically take that unpolarized light from behind you, they turn it into something called circularly-polarized light, which is light where the electric field rotates out a kind of corkscrew shape, they turn it into one handedness of that. So maybe they turn it into left-handed circularly polarized light that hits off that metal electrode at the back becomes right-handed and then get stuck behind the anti-glare filter. It can't get out. So what your anti-glare filter does is effectively polarize the light and trap it inside your display so that you have much clearer resolution and higher contrast when you're looking at an image. Without it, that ambient light would distort what you're trying to look at.
Eva - The light that gets trapped then, does that turn into heat? Where does it go? Does it dissipate?
Jess - It just kind of bounces around. So it just bounces around inside the display, inside all of the different structures. It probably hits off the electrodes again and a little bit will invert the handedness again and then come out. But really there are so many layers of potential optical loss in your mobile phone. And what we're trying to do on a developing new materials side is make sure that they're as streamlined and as efficient as possible. So the light that comes out can all bypass the screen if we want it to, but gets stuck in the screen if we don't want it to distort what we're looking at.
Eva - And so do phones already have anti-glare filters fitted or can we buy extra good ones to stick on the phone screen if you wanted to read on the beach or something?
Jess - You for sure can buy extra good ones. I'm not entirely sure of the optics of all of the different ones that you'd buy, but there are really easy physics experiments you could do to try and understand exactly what they're trying to perform, but actually all smartphones, anything with an OLED organic light emitting diode display should have one of these anti-glare filters inside it anyway. And what we're trying to do on the kind of OLED side, the OLED design side, is make them as efficient as possible. So to make them emit actually twisted light so it can get through that anti-glare filter. So circularly polarized OLEDs are a massive thing, and it's amazing that Joe managed to ask such a perfect question.