# questions about polarization of light **URL:** \ **Category:** Factual Questions\ **Created:** [January 6, 2010, 2:09pm UTC](https://boards.straightdope.com/t/questions-about-polarization-of-light/523899 "2010-01-06T14:09:48Z")\ **Posts on this page:** 4\ **Page:** 2
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 12, 2010, 1:30pm UTC](https://boards.straightdope.com/t/questions-about-polarization-of-light/523899/21 "2010-01-12T13:30:55Z")
I may have misunderstood **Chronos** in my response in post #19… It may simplify matters to consider only one channel - let’s say the one intended for the left eye. The right eye channel is switched off. An image of full movie brightness, polarised a certain specific way needs to be on the screen. The left eye is able to see all (barring small losses) of this image, via the filter in front of it. The right eye is not able to see any (barring small leakage etc) of this image. The filter in front of the left eye is not purposely discarding any of the left-eye-channel image, but this left-eye channel image does need to be at full brightness, so the projector lamp needs to be brighter than normal to compensate for the polarising filter at the projector. If that’s what you meant, **Chronos** , my apologies for not reading it properly. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [January 12, 2010, 11:11pm UTC](https://boards.straightdope.com/t/questions-about-polarization-of-light/523899/22 "2010-01-12T23:11:17Z")
> [@](#): > > Sorry guys – this is a matter of semantics. Assuming that you have perfectly lossless filters, then I maintain that the right eye gets 100% of the light projected in its polarization, so all the loss is taking place at the projector, while the left eye gets 100% of thew light intended for it. > > Of course, your right eye only sees 50% of the light that hits the screen, so you could say that you’re losing 50% of the light there. But it’s all in your definition. If you go around a tree while a squirrel on the other side goes around the tree, keeping it between you and him, have you gone around the squirrel? You can semantically put the losses anywhere you feel like, but the net result ends up being that you need to start with four times as much light as a regular movie, not twice as much, and all the rest of that light ends up getting thrown out somewhere or another. Personally, I would say that some of that loss is at the glasses, since if you had a scene in a 3D movie with no depth (and where the two images where therefore identical), a person without the glasses would see an image twice as bright as would a person with the glasses. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [January 12, 2010, 11:21pm UTC](https://boards.straightdope.com/t/questions-about-polarization-of-light/523899/23 "2010-01-12T23:21:48Z")
> [@Chronos](#): > > You can semantically put the losses anywhere you feel like, but the net result ends up being that you need to start with four times as much light as a regular movie, not twice as much. You mean twice as much for each of the two projectors, totalling four times as much as for a conventional flat movie from one projector with (theoretically) no filters, right? If so, I agree. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [January 14, 2010, 11:49am UTC](https://boards.straightdope.com/t/questions-about-polarization-of-light/523899/24 "2010-01-14T11:49:24Z")
> [@Chronos](#): > > You can semantically put the losses anywhere you feel like […] Do some parts get hot? [Previous page](https://boards.straightdope.com/t/questions-about-polarization-of-light/523899.md?page=1)