a number of differnt common LCD probelms are usualy linked to specific parts of the LCD. the specific problem you are reporting is usualy a sign of either poor manufactureing or an ageing polarization effect. as i'm sure everyone is aware of somthing to dread of any LCD is polarization, where UV light energizes and then melts the crystals into a permenent 'on' position blanking the screen permenently.
In LCD parlance, "polarization" has a very special meaning. Rather than something to dread, polarization is in fact the very basis for LCD operation. You are actually referring to the phenomenon of a cooked display. Such cooking is exceptionally rare in a standard laptop display (it is only somewhat common in projectors), and in any case will not result in the
perfectly regular pattern described in the original post.
another problem that it could be would be missalined prismatic plastic sheets. these shees used to distort and evenly distribute the light form the Cold Cathode Tube. when this happens it causes the light to apear in such a way to exsensuate the areas between the pixels. if you turn the backlight off and shine a bright light onto the screen so you can see the screen without the backlight and you dont see them this is the case. other things related to this layer is if you see large black areas (like a black rectangle drawn on the screen by a program) and it looks like theres tiny multicolored confetti on the screen you cant get rid of. its a coleltion of dust particles between the prismatic layers. cleaning by a skilled tech is required to fix this. it is unpreventable.
Again, you are describing a mechanism that will not produce the perfectly regular grid pattern described in the original post. Of the various hypotheses offered in this thread, Wally's recent supposition about a desktop pattern/display setting issue seems the least improbable.
