Help! The sun is shining! Why can't I see my smartphone screen?
The sun is shining, the sunglasses are out. You go to tweet that perfect summer picture and … wait … you can't see a thing on your smartphone display!
It's not necessarily the phone that's a fault, but how it behaves with your expensive polarising sunglasses.
Polarising lenses on glasses are popular because they reduce the glare, or reflected light, coming off surfaces. They are particularly useful for skiers or drivers for reducing eyestrain, and pretty common on good quality sunglasses.
However, LCD displays also contain polarising filters and it's the alignment of display and glasses that can cause the problem. At a particular orientation, the display will be extinguished, leaving you looking at a black surface, as all the light is filtered out.
Or, in some cases, you'll find everything dims and looks very purple.
Of course, this varies from device to device, and you can easily experiment with your own device - be that smartphone, tablet, or even your laptop - just by holding your polarised glasses out in front and rotating them. At some point, it will just black out.
The MacBook Air, for example, extinguishes at 45 degrees, an angle that's unlikely to be problematic when using a laptop.
Your giant TV extinguishes when viewed in a portrait orientation, again, not likely to be a problem unless you're lying down watching in sunglasses.
For smartphones it's a bigger problem, because they are designed to be used in both orientations, landscape and portrait.
The HTC One (M9) unfortunately dims drastically in landscape when viewed through polarised glasses - exactly at the angle you might want it for taking photos. You can cock your head, or hold it at and angle to get round that, but it's hardly convenient. The Sony Xperia Z3 also extinguishes entirely when in landscape.
The Samsung Galaxy S6, however, does a better job, as does the iPhone 6. Both remain visible in both orientations. You might sometimes see a shimmer, but nothing like the blackout you get elsewhere.
Be aware that it's not only polarisation that causes problems on a sunny day: the display has to have the power to remain visible in brighter conditions, so always remember to try turning the brightness up before you start swearing.
The moral of the story is this: if you have a penchant for polarised sunglasses, be warned, your favourite phone might not like them so much.
And before you ask, most Ray-Ban glasses aren't polarised, unless you've specifically bought polarised lenses. Pair your Ray-Ban aviators with your iPhone and you'll likely be fine.
Pair your Oakleys with your HTC One M9, you probably won't.