Ten years or so ago, when the contrast in monitor screens was not as good as it is today, there was a market for filters to stick on them and make the blacks blacker. Now 3M has introduced a similar kind of filter sheet, but for a different purpose. Today’s reason is security, to prevent people taking a sneak-peek at the screen of your laptop or LCD monitor.
The filter is a thin sheet of plastic which you fix to your screen either with transparent slips of double-sided tape or little adhesive tabs that stick to the screen surround. Both fixings are supplied and both are effective, though they’re also a little tacky (literally). We wonder how cleanly they’d come off if you decided to remove the filter – or move it to another screen – say, a year down the line.
The filter works like this. Imagine a very thin, black Venetian blind set horizontally into the filter sheet, so the ‘blades’ of the blind run from top to bottom. Looking between the blades, you can see the screen clearly, but looking from either side, the blades overlap and you can only see their black sides.
In our tests, the screen grew black quite quickly as soon as we moved off-axis horizontally. We’d estimate the viewing angle with the filter at around 40 degrees either side of perpendicular and 70 degrees without it. The first of the two pictures on this page is taken straight on and the other off-axis, but both are taken with the notebook switched on, displaying the Windows desktop.
So the filter works, at least in the horizontal plane. It’ll make it hard for people, for instance, to look at the screen of your laptop from the seat next to you in a train. It’s not so good in the vertical plane, though, and although 3M talks of preventing ‘shoulder surfing’ in its literature for the filter, it’s not good at preventing somebody taking a peek from directly behind you. It won’t be too good in an office environment, though perhaps the need is less pressing there than on public transport.
The main problem we have with the Privacy Filter is its pricing. It’s effectively a sheet of plastic polarising filter, yet even at Amazon prices the 14.1-inch product we reviewed costs £40, and they range up to £90 for a 19-inch sheet. This seems way too high and we were genuinely surprised they weren’t about half the price.
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