Nov 12, 2013
How to make a computer screen invisible
If you don't want want people snooping on what you're up to on your computer, then you're in luck. A scientist has revealed how to make your screen invisible - or unreadable - to nosy neighbours.
YouTube scientist Brasspup, who specialises in optical illusions on the streaming site, has revealed how to modify an old LCD monitor and a pair of 3D glasses so that only the wearer of the spectacles can see what is on their computer screen.
The secret of why the screen appears blank and white to people who are not wearing the glasses lies in the selective use of polarising filter.
In order to make the modifications, YouTube scientist Brusspup said individuals will need an old LCD monitor, a piece of polarising filter, a pair of 3D glasses, scissors, a prying tool and a craft knife.
In the video, he first prised open and removed the monitor casing, before cutting around the side of the screen. He then stripped the layer of tough film - the top polarising filter - off the screen in pieces. It is this film that allows users of the computer to see what is displayed on their screen. He then set about making the glasses by tracing round the lenses and cutting out the right shapes from a new piece of polarising film. Brusspup removed the 3D film already in place in the glasses and replaced it with the newly cut polarising 'lenses'. After the film was removed from the functioning monitor, it appears white to anyone not wearing the polarised glasses.
The modifications allow the wearer of the spectacles to be the only person to see what is really there on the screen.
An unmodified back-lit LCD monitor typically consists of a layer of molecules aligned between two transparent electrodes and two polarising filters, which are parallel and perpendicular. Light passes through the first filter and is blocked by the second polariser, which makes pixels appear black and explains why when the filter is removed, the screen shows white.
Content is shown on the screen (regardless of whether the filters are in place) by controlling the voltage applied across the liquid crystal layer, so that light can be allowed to pass though in varying amounts and control different amounts of light and dark in each pixel - or minute square area on the screen.