How does a reflective LCD use ambient light instead of a backlight?
In nematic arrangements the crystals are randomly positioned with all their long axes pointing in essentially the same direction, given by a vector known as the director. In smectic arrangements the crystals are further constrained to parallel planes; in smectic A the director is perpendicular to these planes, while in smectic C the director is at some other angle to the planes.
Reflective liquid crystal displays (LCDs) eliminate the need for a power-consuming backlight by utilizing an internal mirror to redirect ambient light toward the viewer.1
In standard reflective configurations, the liquid crystal layer functions as an electro-optical switch between polarizers. When the liquid crystal is set to a bright state, the mirror reflects incoming ambient light back through the display, making the image visible. Because polarizers absorb a significant portion of light, some modern high-quality devices improve brightness by utilizing only a single polarizer.1
Other variations include:
* Guest-host displays: These use dye molecules that change orientation based on an electric field to alter the display's color, also requiring a mirror.1
* Chiral nematic (cholesteric) displays: These do not require a mirror. They use helical molecular structures that spontaneously reflect specific wavelengths of light, switching between a colored reflective state and a scattering state.1
* Transflective displays: These use a partially reflective mirror, allowing the device to switch between reflective mode in bright conditions and a backlit mode in low light to conserve battery life.1