Transflective liquid-crystal display

Reflective (top), transreflective (middle), transmissive (bottom)

A transflective liquid-crystal display is a liquid-crystal display (LCD) that reflects and transmits light (transflective is a portmanteau of transmissive and reflective).[1] Under bright illumination (e.g. when exposed to daylight) the display acts mainly as a reflective display with the contrast being constant with illuminance. Only in dim and dark ambient situations is an auxiliary transmissive backlight needed.

An early application were digital LCD wristwatches. In dim ambient light or at night a pushbutton-activated backlight allowed reading of the display in its transmissive mode.[2] Digital time displays in alarm clocks for bedrooms still work this way. The backlighting is dim, so that the display is comfortably readable at night. Some 21st century smartwatches such as the Pebble Smartwatch also use transflective LCDs.

When an illuminance sensor is added for control of the backlight, such a transflective LCD can be read over a wide range of illuminance levels. This technique is often found in automotive instrumentation. In portable electronic devices the transflective mode of operation helps to save battery charge, since in bright environments no backlighting is required.

The essential component for a transflective LCD is the transflector, a polymer sheet that is reflecting and transmitting at the same time.

Some displays that transmit light and have minor reflectivity are best readable in the dark and fairly readable in bright sunlight, but only under a particular angle; they are least readable in bright daylight without direct sunlight. Under exposure to direct daylight, the image on non-reflective displays will completely wash out.

Trade names

Display manufacturers label their transflective screens under a variety of trade names:

References

  1. ↑ X. Zhu, Z. Ge, T.X. Wu, and S. T. Wu, "Transflective liquid crystal displays", Journal of Display Technology, 1, 15–29 (Sept. 2005).
  2. ↑ U.S. Patent 4,096,550: W. Boller, M. Donati, J. Fingerle, P. Wild, Illuminating Arrangement for a Field-Effect Liquid-Crystal Display as well as Fabrication and Application of the Illuminating Arrangement, filed Oct. 15, 1976.

See also

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