Why Do I Need To Wear Special Glasses To Watch 3D?

Like it or not, you need special glasses to watch 3D TV - Find out why

Man With 3D glasses
Getty Images - Albert Mollon - Moment Collection

3D TVs were discontinued in 2017. Although there were several reasons for its downfall, one cited by many consumers was the need to wear special glasses. To add to the confusion, many don't understand why glasses are needed to view 3D images.

Two Eyes – Two Separate Images

The reason that humans, with two functioning eyes, see 3D in the natural world, is that the left and right eyes are placed a distance apart. This results in each eye seeing a slightly different offset image of the same natural object(s).

When our eyes receive reflected light bounced off objects, it contains not only brightness and color information but also depth cues.

The eyes send the offset images to the brain, which combines them into a single 3D image. This enables us to not only see the shape and texture of objects correctly but also allows us to determine the distance between objects within a natural space (perspective).

Since TVs and video projectors display images on a flat surface there are no natural depth cues that allow us to see texture and distance correctly. The depth we think we see is derived from the memory of how we have seen similar objects placed in a real setting, along with other possible factors.

To see displayed images on a flat screen in true 3D, they need to be encoded and displayed on the screen as two off-set or overlapping images which then has to be recombined into a single 3D image.

How 3D Works with TVs, Video Projectors, and Glasses

The way 3D TVs and video projectors work is that there are several technologies used for encoding separate left and right eye images on physical media, such as Blu-ray Disc, cable/satellite, or streaming.

The encoded signal is sent to the TV. The TV decodes the signal and displays the left and right eye information on the TV screen. The decoded images appear as two overlapping images that look slightly out of focus when viewed without 3D glasses.

When a viewer puts on 3D glasses, the lens over the left eye sees one image, while the right eye sees the other image. As the left and right images reach each eye via the 3D glasses, a signal is sent to the brain, which combines the two images into a single image with 3D characteristics. The 3D process fools your brain into thinking it is seeing a real 3D image.

Depending on how a TV decodes and displays the 3D image, a specific type of glasses must be used to see the 3D image correctly. Some manufacturers, when they were offering 3D TVs (such as LG and Vizio) used a system that requires the use of Passive Polarized Glasses, while other manufacturers (such as Panasonic and Samsung) required the use of Active Shutter Glasses.

For more details on how each of these systems work, along with advantages and disadvantages, read All About 3D Glasses

Auto-Stereoscopic Displays

There are technologies that enable you to see a 3D image on a TV without glasses. Usually referred to as "Auto-Stereoscopic Displays", prototype and special application units are used primarily in commercial, industrial, educational, and medical settings. They are extremely expensive and, in most cases, you have to view from or near the center spot, so they are not good for group viewing.

No-glasses 3D is/has been available on some smartphones and portable game devices and has been demonstrated on larger screens as Toshiba, Sony, and LG first showed prototype glasses-free 56-inch 3D TVs in 2011 and Toshiba showed an improved model in 2012 that was available in limited quantities in Japan and Europe but has since been discontinued.

Since then, Sharp and Samsung have shown no-glasses 3D on several 8K prototype displays, and Stream TV Networks is on the forefront of bringing glasses-free TVs to the commercial and gaming space.

3D advocate, James Cameron, is pushing research that could make glass-free 3D available for movie theaters in time for one or more of his forthcoming Avatar sequels.

Auto-Stereoscopic display technologies are being implemented where it is practical, but you may start to see it being offered on a retail basis. Production cost and demand may end up being determining factors with regards to future availability.

Until that time, glasses-required 3D is still the most common method of viewing 3D on a TV or video projector. Although new 3D TVs are no longer available, this viewing option is available on many video projectors.

For more on what is required to view 3D, and how to set up a 3D home theater, refer to our Complete Guide To Watching 3D at Home.