Malus's Law is an equation that describes how much light intensity that a beam of light will lose if if it goes through a polarizer, dependent on what angle the polarizer is at relative to the light. It is explained better than I ever could here: http://en.wikipedia.org/wiki/Polarizer#Malus.27_law_and_other_properties But what about a scenario like this? If you have unpolarized light, pass it through an ideal polarizer, it loses half of its intensity (explained in the above link) and all the light is now polarized. Now pass the light through another polarizer that's oriented 90 degrees from the original one. By Malus's Law, or just by the nature of EM waves, all the light is gone, and light intensity is effectively 0. But... if you add a third polarizer that is oriented 45 degrees from the first polarizer, the light seems to lose half its intensity each time (cos(45-0)^2 = 0.5 and cos(90-45)^2 = 0.5), which means after it goes through all 3 polarizers, it has one-fourth the light intensity of the original incident light. Does that mean the addition of another polarizer made it so that more light passes through?