Often times its duplexing the polarization, as both the glasses and the screen probably have a polarized film on them, and they're working at such an angle as to produce even further interference.
Take a look at your cell phone's display too...turns all sparkly or black if you have a sanyo 5150 But yeah, if I look straight on though my polarized glasses my screen is black. I can see mine perfectlyl from a 45ish degree angle.
PoBoy
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I'm a ghost...email me if you have any questions on my old setup