Active 3D Glasses vs. Passive 3D Glasses

With all the new 3D TVs on display at CES we are getting a lot of questions about 3D viewing. One of the most common is whethr or not you will have to wear glasses to watch 3D, the answer to that one is still yes. After that people want to know what will be the best way to watch 3D content. We've compared the different technologies and now we'll compare the glasses you use to watch them.

Passive 3D Glasses

Passive 3D glasses are any 3D glasses that don't require a power source to view 3D content. The two major types of passive glasses are anaglyph and polarized 3D glasses. One of the main benefits to passive 3D glasses is cost. Since they do not require a power source or powered lenses, passive 3D glasses can be very inexpensive. Anaglyph glasses, commonly seen with one red and one cyan lens, are often seen made out of cardboard with cellophane lenses. Though anaglyph glasses do show the viewer a 3D image it is the least advanced of all methods of delivering 3D and because they use color to separate the images some or all color information is lost to the viewer.

Polarized 3D glasses come in two forms, linear polarized and circular polarized. Linear polarized glasses require the use to maintain a vertical head position, tilting your head left or right can break the 3D effect because the content relies on one eye seeing the vertically polarized image and the second eye seeing the horizontally polarized image. When the head is tilted the polarized lenses no longer line with the polarized double image on the screen. Circular polarization does away with this problem but it requires a special projector and filter and will not be used on 3D televisions.

Another benefit to passive 3D glasses is that since the viewer is being shown both images at once it does not half the frame rate of the content like active glasses do.

Active 3D Glasses

Active 3D glasses require a power source to power the lenses in the glasses, for shutter glasses a mechanism to sync the glasses to the display is also required. Head mounted displays are considered active 3D glasses but since they contain a pair of displays built into the device they are not relevant to this discussion.

Shutter glasses are the active 3D glasses most viewers will use for 3D content, they use LCD lenses that are commanded to alternately open and shut each lens to show each eye a different image. It used to be that shutter glasses were connected by a wire that provided both synchronization and power but now most shutter glasses are powered by small batteries and receive sync signals via an infrared beam similar to a TV remote. The technology involved makes shutter glasses considerably more expensive than passive glasses, expect to pay anywhere from $50 to $100 for a pair of shutter glasses. Most new 3D TVs will include one pair of glasses but additional pairs must be purchased separately.

The major disadvantage to active 3D glasses is that the separate images for each eye are not delivered at the same time. The content will alternate the images shown to each eye at whatever the frame rate of the content and refresh rate of the display offers. For example, with 60 frame per second content each eye is being shown only 30 images per second effectively halfing the frame rate seen by the viewer. This is most noticeable during slow camera pans or during fast motion. The higher the frame rate the smoother each of these actions will appear so active 3D glasses can show slight to noticeable judder effects during these scenes.

Active 3D glasses allow full color and picture information since both images are not being overlayed on one another and we feel that this benefit outweighs the effect that active glasses have on frame rate. Until 3D without glasses is commonplace shutter glasses should provide the best home 3D experience. For more information on 3D glasses and how they work see our 3D Glasses - Active and Passive, Polarized, Shutter and Color Anaglyph 3D Glasses article.