Yeah, I suppose I deserve the down-vote, too much snark. Apologies! Especially due to this info alok-g linked: http://en.wikipedia.org/wiki/Liquid_crystal_display_televisi... Important bit: 3M suggests that, on average, only 8 to 10% of the light being generated at the back of the set reaches the viewer.
I'd always thought they were more transparent than that, given that I've seen LCD screens used as projectors: http://www.instructables.com/id/DIY-LCD-PROJECTOR/ in which case (though there's no way to detect how bright the box behind it is) a highly-transparent screen could indeed be a fairly significant breakthrough.