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A pair of CrystalEyes shutter glasses

LCD shutter glasses are glasses used in conjunction with computers to create the illusion of a three dimensional image, an example of stereoscopy. Glass containing liquid crystal and a polarizing filter has the property that it becomes dark when voltage is applied, but otherwise is transparent. A pair of eyeglasses can be made using this material and connected to a computer video card. The video card alternately darkens over one eye, and then the other, in synchronization with the refresh rate of the monitor, while the monitor alternately displays different perspectives for each eye. This is called Alternate-frame sequencing. At sufficiently high refresh rates, the viewer's visual system does not notice the flickering, each eye receives a different image, and the effect is achieved.

The problems associated are the cost for the additional equipment (typically up to US$100), and that the flickering can be noticeable if the refresh rate is not sufficiently high, as each eye is effectively receiving only half of the monitor's actual refresh rate. As with other single image methods the brightness is considerably diminished.

Another possible effect is "ghosting". Since the opaque phase of the LC still permits a small amount of light to transmit, some users experience secondary "ghost" images from the alternate channel. This effect can be exacerbated by persistence effects in the phosphors of the CRT, causing images to "bleed" over into the other channel.

Until recently, the method only worked with CRT monitors; some modern flat-panel monitors now support high enough refresh rates to work with some LC shutter systems.

Another potential use of shutter glasses is to allow private viewing of a publicly observable screen (e.g. a laptop on a train). The display could flicker between the normal display and the normal display's photographic negative image. To the unaided eye this screen would appear a blank grey. The screen, viewed via shutter glasses blocking out the negative image, would appear to show only the private image.^{[citation needed]}