Optical activity, red light. Chiral molecules (e.g., sugar) cause rotation of the plane of the linearly polarized light when it passes through the sample. Optical activity of sugar is demonstrated by placing a beaker with corn syrup on top of an iPad. Its LCD screen acts a source of linearly-polarized red light. An analyzer (linear polarizer) is placed on top of the beaker. First the analyzer is rotated so that minimal amount of light passes from the screen and through the analyzer, BUT NOT through the sample (top frame). Then the analyzer is rotated so that minimal amount of light passes through the sample AND the analyzer (bottom frame). The difference between the two analyzer positions is the rotation angle.