3D glasses work by providing a separate image to each eye. The brain then combines the two images into a single image with 3D characteristics. The 3D process fools your brain into thinking it is seeing a 3D image, so it creates one for you.
3D-enabled TVs and 3D-enabled Video Projectors work by incoming 3D signal that can be encoded and sent in several different ways. The TV or projector has an internal decoder that takes the 3D signal and displays the left and right eye information on the TV screen in such a way that it appears to look like two overlapping images that look slightly out of focus.
One image is intended to be seen only by the left eye, while the other image is intended to only be seen by the right eye. In order to view this image properly, the viewer must wear glasses that are specially designed to send the left and right eye images properly to the left and right eye. When viewing the overlapping images through these special glasses, the image appears to be in 3D.
Types of 3D Glasses
Glasses used for viewing images displayed on a 3D TV or 3D video projector screen are of two types:
Passive Polarized glasses that look and wear much like sunglasses. They usually have enough front space to place over existing eyeglasses for those than need to. These type of glasses are inexpensive to manufacture and can range in price from $5 to $25 for each pair depending on the frame style (rigid vs flexible, plastic vs metal).
Active Shutter glasses, which are slightly bulky, since they have batteries and a transmitter that synchs the rapidly moving shutters for each eye with the onscreen display rate. These type of glasses are also more expensive than passive polarized glasses, ranging in price from $75 to $150 depending on the manufacturer.
Advantages of Passive Polarized 3D Glasses:
2. Inexpensive - About one third, to one quarter the price of Active Shutter glasses.
3. No flickering - which means less discomfort and eye fatigue over long view periods.
Disadvantage of Passive Polarized 3D Glasses
The 3D image that is viewed is one-half the resolution of a 2D image displayed on the same television (although proponents of passive glasses dispute this). This is because both left and right eye images are displayed on the screen at the same time. Check out the two sides of this issue represented by Joe Kane and Dr Raymond Soneria.
The presence of horizontal lines on the screen and some jaggie artifacts can be noticeable, most notably with text and straight line geometric shapes.
Advantage of Active Shutter 3D Glasses:
The 3D image resolution is the same as the 2D image displayed on the same television. This is because the left and right eye images are displayed in a sequential fashion, in synch with TV or projector's screen refresh rate and the opening and closing of the LCD shutters in the glasses.
Disadvantages of Active Shutter 3D Glasses:
1. Flickering due to rapid opening and closing of the LCD shutters may be detectable by some viewers, causing discomfort.
2. Heavier and Bulkier than Passive Glasses
3. Battery power required.
4. Expensive - Two or three times the price of Passive Polarized Glasses.
The Glasses Have to Match the TV or Video Projector
Depending on which brand and model TV or video projector you buy, will determine which type of glasses (passive polarized or active shutter) you will be required for use with that TV or video projector. So far, manufacturers, such as Mitsubishi, Panasonic, Samsung, and Sharp appear to be taking the Active Shutter glasses route to their 3D products, at least with regards to LCD, Plasma, and DLP televisions, while LG is now actively promoting Passive Glasses for their uncoming 3D LCD TVs, and Toshiba and Vizio has some LCD TVs that use Active Shutter Glasses and others that use Passive Glasses.
Some manufacturers may provide glasses with the set, or they may be an accessory that must be purchased separately. It is anticipated that those manufacturers that do end up providing glasses with their sets will provide one or two pairs, with the option of purchasing additional pairs as desired. Prices for the glasses will vary, at both the manufacturer's discretion and what type they are. As mentioned above, active shutter glasses will be more expensive (probably $75-$150 a pair) than passive polarized glasses ($5-$25 a pair).
Also, another factor to take into consideration is that glasses branded for one manufacturer may not work another's 3D-TV or video projector. In other words, if you have a Samsung 3D-TV, your Samsung 3D glasses will not work with Panasonic's 3D-TVs. So, if you and your neighbors have different brand 3D-TVs, you will, in most cases, not be able to borrow each other's 3D glasses. For more details on why 3D Glasses for one brand 3D-TV may not work with another 3D-TV, check out the report from Big Picture and Sound.
However, XpanD, a third party company that makes 3D glasses for both commercial and consumer applications, and Monster Cable have introduce Universal 3D Glasses that can work on most currently available 3D TVs that use the Active Shutter system. For more details, check out the XpanD Universal 3D Glasses and Monster Cable 3D Glasses product pages. Compare Prices For XpanD Universal 3D Glasses - Compare Prices for Monster Cable 3D Glasses.
For an additional perspective on implementation of Passive vs Active 3D Glasses technology, check out a 2011 report from TWICE (This Week In Consumer Electronics) that tries to address the validity of advertising claims by proponents of Active and Passive 3D technology.
3D Without Glasses is Possible But Not Practical...For Now
There are technologies that enable viewing of 3D images on a TV without glasses. Such prototype and special application units exist, usually referred to as "AutoStereoscopic Displays". Currently, these displays are extremely expensive and, in most cases, you have to stand right in the center spot, so they are not good for group viewing.
However, progress is being made as no-glasses 3D is becoming available on some cellphones and portable game devices and has been demonstrated in a larger screen TV screen form factor as Toshiba, Sony, and LG all showed prototype glasses-free 56-inch 3D TVs at the 2011 Consumer Electronics Show. In addition, at the more recent CES 2012, Toshiba demonstrated its first "market-ready" no-glasses 3D TV, but from its demonstrations, it still needs some additional refinement.
Although autostereoscopic display technologies are being pursued and implemented in some settings, this approach to 3D viewing still needs to be further perfected, and the price needs to be affordable, if it is to be sold successfully in stores. However, the progress so far is encouraging.
For more details on the current state of no-glasses 3D viewing, refer to my FAQ: Can I Watch 3D Without Glasses?
For an in-depth look at what else you need to know about 3D, check out my Complete Guide to Watching 3D at Home.