There are two basic types of 3D glasses (there are more but in practice, these two are the most significant). And they are designed for two different types of stereoscopic projection.
One type, those used by the vast majority of cinemas, are termed passive glasses. They are single-use and are bagged when given to the customer.
Their advantage is that they are very light and inexpensive. They have various drawbacks. Chief of these is that they don't give very bright vision. Another important drawback is that if the spectator is sitting away from the central point of the auditorium, his or her vision of the other side of the screen darkens considerably. This is because the screen is treated with metal as passive glasses work through polarization of the image. Finally, this type of projection causes substantial "ghosting". "Ghosting" is when one eye sees part of the image that is intended to be seen by the other eye. It is a quite annoying kind of "double image". The word comes from the English "ghost". The cost price of passive glasses is approximately 0.40 Euros per unit.
The glasses that we use in our cinemas are active. They are reusable and, between projections, we wash them and sanitize them scrupulously, one by one. Our apparatus for cleaning and drying by centrifugation is spectacular.
The glasses that we currently use function by liquid crystal and, corresponding to infra-red signals received from the projector, they open and close the vision of each eye 72 times per second, 144 times per second in total. This results in a much brighter stereoscopic effect, no shadows on the screen and minimal "ghosting". The cost price of the active glasses that we use is currently 44 Euros per unit. And we can affirm that they are very easily broken...
Their main drawback, asides from the price, is their weight, which is primarily due to the need to make them watertight. This sealing is required to allow the cleaning of glasses without affecting the battery inside. New models of lighter active glasses are appearing, designed for the 3D television market. We are experimenting with different models and when we find one which is lighter and which maintains the same quality of image and seal as our current glasses, you can be sure that we will not hesitate to introduce them.
For this reason, the quality of 3D image which you enjoy in our cinema is incomparably higher than "standard". For this reason and, mainly because the auditoria are designed to ensure that the spectator is more immersed in the image. the glasses you are provided with at the entrance to the auditorium must be scrupulously clean; and if they are not, we ask that you bring this to our attention, and we will take the appropriate steps. We cannot claim to offer the best quality of existing 3D image and then fail in the most obvious, the cleanliness of our glasses.