Reflective Digital Displays

Our daily experience is typically with displays that emit light, our phones, televisions, monitors, tablets and watches all use technologies such as LCD (with LED backlights) or OLED or direct view LED. However reflective displays are also commonplace, calculator displays, shelf-edge labels, and of course Kindle e-readers. But there is significantly more potential for reflective displays, especially for outdoor signs where their significant benefit of being sunlight readable and low power provide considerable opportunity.

My first imaginings of the future of displays were along the lines of living room walls and cereal boxes being turned into displays, the stuff of science fiction. Nearly 50 years later we are still not at that stage, not commercially in any case. Well before knowing the terminology or the implications concerning power, ambient light, etc, I favored the idea of e-paper as the future of display technology. Today, after many years in the display industry, I am more pragmatic and favor whatever best meets the needs of the application and is actually available, but reflective displays are a key part of the display technology mix.

There are a number of reflective display technologies that have been proven and commercialized to various extents:

LCD

e-paper (charged particle)

Electro-wetting

Electrochromic

Other: Electromechanical

There are some very significant benefits to these reflective display technologies for certain applications, for example outdoor signage where they offer:

Excellent visibility in sunlight. This compares with emissive displays that are competing with the ambient light.Very low power. The reflective display technologies typically only use power to change the image or require a very small amount of power to maintain their image. The clear benefit of this is that they can be installed in locations where they are dependent on solar power.

LCD is best known as an emissive display technology for its use in televisions and mobile devices, it normally has a backlight and is part of an emissive display assembly. However LCD doesn't emit light, the backlight to the display assembly provides the light, and these days that is usually made using LED, the LCD acts as a shutter allowing light to pass or not. LCD can work very effectively as a reflective display but efforts to make large or color reflective LCD displays have not been particularly successful (so far). There is a hybrid known as transflective, this can operate as both reflective and backlit. Otherwise reflective LCD is used extensively in shelf edge labels, calculators and watches.