The molecules along the upper plate point in direction 'a' and those along the lower plate in direction 'b,' thus forcing the liquid crystals into a twisted structural arrangement. When the molecule arrangement is twisted 90 degrees as shown in the figure, the light also twists 90 degrees as it passes through the liquid crystals. Molecules rearrange themselves when voltage is applied When voltage is applied to the liquid crystal structure, the twisted light passes straight through. The molecules in liquid crystals are easily rearranged by applying voltage or another external force. Blocking light with two polarizing filters When voltage is applied to a combination of two polarizing filters and twisted liquid crystal, it becomes a LCD display.
Light passes when two polarizing filters are arranged with polarizing axes as shown above, left.
Light is blocked when two polarizing filters are arranged with polarizing axes as shown above, right. A combination of polarizing filters and twisted liquid crystal creates a liquid crystal display. When two polarizing filters are arranged along perpendicular polarizing axes, light entering from above is re-directed 90 degrees along the helix arrangement of the liquid crystal molecules so that it passes through the lower filter. When voltage is applied, the liquid crystal molecules straighten out of their helix pattern and stop redirecting the angle of the light, thereby preventing light from passing through the lower filter. In a TN type LCD, liquid crystals in which the molecules form a 90-degree twisted helix, are sandwiched between two polarizing filters.