Sunglasses and LCD screens?

Okay, Teeming Millions. I own an ordinary laptop with an Intel 915 GM/GMS screen. I also own a pair of sunglasses. When I am at my computer and wearing my shades, should my head tilt to the left (my right ear above left ear), the screen will start to darken, and as I tilt my head it will get darker, and then start to get lighter again as my head reaches a painful 90 degree angle. If I tilt my head left, this doesn’t happen - in fact, it gets lighter to a point.

Now here’s the wierd part. I also own a flatscreen LCD TV, and as I tilt my head right while wearing my shades (my left ear above right ear), it gets dark! What gives? Why do LCDs do this?

The LCD screen is polarized, as are your sunglasses. Take two pair of sunglasses and look through two lenses at once rotate. Rotate one of the pair of sunglasses. There will be an angle at which almost all light is blocked, the same as with your LCD screen.

Your sunglasses have polarized lenses. Mine do the same thing. I notice it particularly with the screen on digital cameras.

For the sunglasses to have this effect, I presume that the light from the LCD screen is also polarized, so you are observing destructive interference.

In case you don’t know what polarized light is, almost all the light waves are in the same plane of travel. The filter lens will only let the light through that lines up with the slit like structure on the lens. Glasses would block all light when miss aligned , if the polorized light and the polorized filter were perfect and the allignment of by a little bit. You get the darkening effect instead as the allignment gets worse. You can make pictures on glass plates by, putting layers of cellophane tape on them. As the light passes through the layers of tape it rotates more or less with the tape thickness. You sent the polorized light through the slid and then view it through the polorized lens. A polorized light source can be made by shining a flash light through a lens.
Sorry if that was to much information for you.

How LCD works. An LCD display consists of a liquid crystal panel between two linear polarizers, so all LCD displays produce polarized light.

Sunglasses are polarized because light reflecting off of translucent material (e.g. water), as well as light scattered by the sky, are both polarized. A polarizer prefrentially blocks light from such sources.