How to Choose 3D Glasses – Passive Polarized vs Active Shutter 3D technology

3D glasses form a vital component of current 3D Display technology enabling stereoscopic vision and depth perception. As explained in greater depth in the 3D TV technology guide, we are able to perceive depth due to the fact that each of our eyes observes the same scene but at a slightly different perspective. When the individual images being viewed by each eye reaches our visual cortex, our brain automatically puts these images together and interprets information regarding the third dimension. Try tossing a ball back and forth with a friend with one eye shut and you will realize just how important the second eye is for us to perceive depth.







Panasonic’s Active Shutter 3D Glasses

Thus, ultimately any 3D display technology will rely on using a method to deliver separate images (or views) of the same scene to each eye. 3D glasses provide a very simple and elegant approach to achieving this. The idea behind them is simple enough, each eye piece allows the image meant for the corresponding eye to pass through while blocking the image meant for the other eye.

3D Glasses can be divided into two primary technologies, Active and Passive. Active glasses are usually powered and involve moving or switchable elements in the glasses that “actively” discriminate the incoming image so as to provide a different image to each eye. In direct contrast, Passive glasses do not rely on any powered or movable elements. They usually rely on some special type of optical material that helps discriminate between the images meant for each eye.

Active Shutter 3D Glasses

Active shutter glasses are currently a very popular choice amongst consumer electronics giants who are investing in 3D display technology. The primary reason for this is that this technology requires a very minimal modification to current HDTV displays and as a result it is much easier to develop and perfect. The individual eye pieces of these glasses incorporate liquid crystals and a polarization filter so that when a voltage is applied, the glass turns dark and prevents light from transmitting through. Thus the left and right eye glass can be shuttered alternatively in this manner and this shuttering effect is synced with the refresh rate of the display. The 3D TV displays a frame for the left and right eye alternatively and the sync with the active shutter glass ensures that each eye only ever views the image it is meant to see. As is probably evident, because of the way these displays work, the effective refresh rate of the TV is halved. This is why 3D Ready TVs have to have a minimum refresh rate of 120 Hz (meaning 60 frames per second for each eye).

So how will Active Shutter Glasses affect your 3D experience? Well, it is actually a very simple and elegant solution to providing stereoscopic vision using existing display technology. The pros and cons of this technology is listed below and will probably help answer some of your questions.

Advantages of Active Shutter Glass Technology
  • Probably the cheapest 3D technology in the short term. This is because this technology only needs a refresh rate enhancement for current LCD and Plasma TVs, something that isn’t too hard or expensive to do. In addition a syncing unit will be required to sync the TV to the active shutter glasses
  • Lower price point does not come at the expense of 3D image quality.
  • Backward compatible with some of the high-end 3D capable TVs that were sold in 2008 and 2009
  • Displays are based on very mature LCD, DLP and Plasma technology which means that most of the quirks are already ironed out and prices shouldn’t be prohibitive.

Some drawbacks of Active Shutter glasses

  • The constant shuttering might bother some who are very sensitive to low refresh rates and cause flickering. This will be true of the lower end 120 Hz displays which only provide an effective refresh rate of 60 Hz. However, 3D display manufacturers have already announced many TV models with refresh rates of 240 Hz and even 480 Hz! These high refresh rates will easily get rid of any such complaint one might have of the 120 Hz displays
  • Glasses are battery powered. This is one major drawback that is not particularly easy to alleviate. Due to the nature of the technology the glasses need to apply a potential to “shutter” the glasses. It also needs additional power to communicate and sync with the TV. Running low on batteries while watching a movie will surely be a very annoying experience. So if you are planning to buy one, be prepared for this. It shouldn’t be hard to deal with though. It’s just like your PS3/XBOX360 wireless controllers to be honest. Just set them up at the charging dock when you aren’t watching 3D television, and that should make sure that they are charged and ready to go when you need them
  • While the 3D displays using this technology will be inexpensive themselves, the glasses will be more expensive than their passive counterparts due to their complexity. This means that it might be a bit prohibitive to own many active shutter glasses for when you have friends come over to watch a 3D movie. However, it is most likely that they will be well subsidized by the display manufacturers in an effort to encourage widespread 3D TV adoption.

That pretty much sums up the active shutter technology and its pros and cons. It is definitely the most mature 3D technology at the moment when it comes to personal 3D capable home theater systems for the home user and promises a fantastic 3D experience.

Passive Polarized 3D Glasses

RealD Polarized 3D Glasses


The simplest passive 3D glasses that most of us are all familiar with are color anaglyph glasses…those cheap red-green or red-cyan glasses that you have used at some point or the other. These glasses do not have any “active” or powered components on the glasses. Instead, they rely some optical effect to discriminate between two images projected on a screen, each meant for a different eye. In the case of anaglyph glasses, the images for the left and right eye were projected using two projectors on the same screen and due to the color tints on each eye piece, a separate image was delivered to each eye. However, this technology has severe limitations, chief amongst them being the poor color fidelity due to the use of tinted glasses. The muted colors lead to a very surreal, uncomfortable and visually jarring 3D experience which prevents the viewer from being immersed in the 3D environment.

More recently, there has been resurgence in Passive 3D Glasses technology due to technological progress that has enabled Digital projectors such as those used by RealD and IMAX 3D to display commercial movies at movie theaters in true 3D. These systems rely on exploiting a property of light called polarization. If you are interested in the details of this technology check out my article explaining how 3D TV technology works. To explain it very generally, this technology relies on discriminating between two images projected on the same screen by 2 separate projectors based on the polarization of the light used to project the image. As shown in the figure below, when light of one polarization encounters an eye-piece that is polarized in the opposite direction, it cannot pass through. On the other hand, if both the lens and the light have the same polarization, then the light passes through the lens unimpeded. Thus, each eye piece has the opposite polarization and the image projected on the screen consists of two images, each possessing a different polarization and perspective, meant for one eye. In this manner, a separate image is delivered to each eye.

In commercial 3D projectors used in theaters, the projector technology relies on Circularly polarized light which works in a similar manner but also allows the viewer to tilt his or her head without degrading the image quality. These projectors also save on costs since they can alternatively generate right circularly polarized and left circularly polarized images in rapid succession without the need for two independent projectors.

We have listed the advantages and some of the disadvantages of this technology below

Advantages of Passive Polarized 3D Glasses

  • Provides excellent rejection between the left and right eye views thus getting rid of any ghosting issues in the 3D videos
  • Guaranteed flicker free 3D experience
  • Provides amazing visuals and very rich colors
  • Passive 3d Glasses are extremely cheap. You can easily stock up on them if you are planning to have a big Super Bowl party where you want to show off your fancy 3D TV. Additionally, there is a good chance that the glasses you kept from when you went to the theater will actually work for your passive polarized 3D display

Some disadvantages to keep in mind

  • This technology is currently limited to front-projection systems. This means that it is easier to use in projectors but hard to implement in regular flat screen 3D Tvs. This is primarily because it is very hard for the light to retain it’s polarization property when it interacts with a screen. For front-projection systems, a special silver screen is used to reflect the light while maintaining the polarization of the projected images.
  • This projection technology is currently very expensive and will appeal only to the hardcore 3D addicts out there. Silver screens aren’t cheap either!
  • This technology is not compatible with current mature display technologies such as LCD, Plasma and DLP. This means that any new technology that is developed will still be in “Beta” mode and will probably take a couple of years before the kinks are ironed out.

The Verdict

So which type of 3D display technology should you go with? As things stand at the moment, we would very strongly recommend Active Shutter based 3D TVs. As listed above, this is based on very mature and robust display technologies and will also be very competitive when it comes to pricing. While passive polarized glasses are attractive in their passive nature, this display technology will still take a few years to mature before it will truly challenge active shutter based systems. Of course, chances are that in the next few years someone will develop a 3D TV that doesn’t require glasses… Well, at least we can hope that they do :-) .


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