Passive 3D glasses, also known as polarized 3D glasses, are glasses that allow viewers to watch movies or television in 3D without actively changing the picture as viewed through the lenses as the movie progresses. These types of glasses include both the paper frames with red and blue plastic lenses that used to come in children’s magazines and the more high-tech plastic and metal frames that resemble sunglasses. The red and blue-lensed paper glasses are disposable and have remained a niche form of 3D technology. The passive 3D glasses that come with 3D televisions are reusable and have lenses that, to the untrained eye, look exactly the same and do not have different colors.
Active 3D glasses have circuitry that works in concert with the television to actively — hence the name — change how the lenses present the view of the screen to the wearer’s eyes. This process continues throughout the film or program, with instructions from the television to the glasses causing the lenses to change in undetectable increments. Passive glasses have that name because there’s no activity in the lenses or frames. All the activity that enables the wearer to see the 3D effects is in the wearer’s eyes and brain. The glasses do nothing.
There are a number of benefits to using passive 3D glasses instead of active 3D glasses has a number of benefits, not the least of which are cheaper cost and lighter weight. The glasses don’t require any power or moving parts, so the cost of manufacturing them is substantially less than that of active 3D glasses. Those passive glasses that cost a lot are those that have the fancier bells and whistles, such as clip-on lenses or special styling. The lack of circuitry contributes to the lightweight nature of the glasses, making it easier to wear them for a longer time. Some brands of passive glasses look like plain eyeglasses, too, instead of something out of a science fiction movie.
One of the downsides to these types of glasses is that they can make a video appear slightly fragmented, as if lines were running across the screen. The extent to which this happens varies from brand to brand, so consumers have to test each model when they buy a pair, rather than going solely by price and style. Another disadvantage is that passive 3D glasses can worsen the picture quality because of the optical effects from the lenses.
