Posted: Jul 30, 2011 4:02 am
by byofrcs
When you close one eye then the open eye is the only one providing data to the brain. The light that travels through both lenses will lose both polarisations and so will be blocked. The light that has only gone through one lens will just be polarised to one plane. Ergo the light on the closed eye lens will be blocked i.e. appear black as it has passed through both lenses.

With both eyes open the brain gets signals from both eyes and it has this pretty nice trick of mixing the images to create one image. So where it has no signal it is happy to fill it in. It thus layers the image of the eye that is working over the missing light so it appears normal to you.