As an LED display manufacturer, NanoLumens is predictably most focused on emissive display technologies or those that create and emit light of their own. LED displays are an example of such a display technology, hence the “E” in the acronym, which stands for Emitting. Emissive display technology is of course not the only display technology out there however, so I’d like to take the opportunity to briefly touch on an alternative display technology, how it works, and what makes it different. The technology I’ll be covering here is that of reflective displays, and in sharing my thoughts I simply hope to assist display owners in understanding the range of options they face so they can make informed purchase choices.
What Are Reflective Displays?
Reflective displays are a digital display solution that reflects the ambient light of its surroundings rather than creating and emitting light of its own. This non-emissive technology is frequently referred to as electronic paper due to the way its appearance mimics that of traditional ink on traditional paper, which makes its content substantially more legible in environments with high levels of ambient light. Consider the bright environment efficacy of the most recognizable application for this technology, e-reader tablets like the Kindle, in contrast to that of an LED, LCD, or otherwise backlit display. Amidst bright sunlight, like at the beach for example, the backlit products will shine far brighter but their content will likely be more difficult to view. This is because while emissive displays must outshine the ambient light around them, reflective displays draw their brightness from the ambient light.
Reflective displays are a digital display solution that reflects the ambient light of its surroundings rather than creating and emitting light of its own.
How Do Reflective Displays Work?
Unlike an emissive display, which creates its own light through electroluminescence, reflective displays simply redirect and repurpose the light that already exists around them. This style of reflective display technology was originally pioneered in the 1970s by researchers at Xerox, who found that by embedding microscopic polyethylene two-colored spheres (Janus particles) within bubbles of oil arrayed across a transparent silicon sheet, they could manipulate the rotation of the spheres to show one color or another. On one side of these spheres was negatively charged black plastic, while the other side featured white plastic with a positive charge. The researchers discovered that by adjusting the polarity of the potential applied to the electrode layers encasing the layer of sphere-filled bubbles, they could alter which side of the spheres faced up. This binary system allowed for the display of rudimentary images, and more importantly, of text. This packaging process is very different from the LED packaging process, detailed here.
Other variations of electronic paper have since evolved, with many making use of electrophoresis, the process by which particles within a fluid migrate within that fluid when influenced by an electric field. This approach replaced the original polyethylene spheres with titania particles and added a dark dye (among other agents) to the oil within which these particles floated. When the potential was applied to the conductive plates encasing this liquid concoction, the titania particles would either migrate to the viewing side of their encasements or to the rear. Cells with particles at the viewing side will appear white to viewers, who receive the reflection of ambient light off the white-colored particles. Cells with particles at the rear will appear dark to viewers as the ambient light is absorbed by the dark dye rather than reflected. This dyed oily mixture is the electronic ink you may have heard tell about. E-readers are a common commercial application of this electrophoretic display (EPD) technology.
Note that there is no light created throughout this process. The potential applied to the electrode pairs within the display system simply manipulates the orientation of the encased particles, which then reflect or absorb ambient light the same way traditional paper would. Switching the e-ink “on” or “off” typically takes a second or so, which explains why EPD products don’t refresh quite as quickly as emissive devices. EPD products are vastly more energy-efficient however, since the potential is only required when content needs to change, whereas emissive devices require a constant flow of energy to create their light (when in use).
Will Reflective Displays Replace Emissions?
In short, no. But that is large because they are not trying to. As things currently stand, reflective displays and emissive displays are simply targeting different applications. NanoLumens has investigated the potential for e-ink in larger format applications but found it less than ideally suited for the sorts of environments in which NanoLumens typically installs. Unless tiling reflective displays becomes a financially viable and technologically feasible solution, this will likely remain the case for the near future. For all its merits in high-bright environments and hand-held applications, e-ink predictably struggles in lower light or dynamic light settings, making it a less effective solution for large-format markets like sports or casinos. These vibrant environments also require vibrant content, and reflective displays fall short in that regard for several reasons. For starters, their refresh rate is inherently slow at around a full second, meaning traditional video content running at 60 frames per second is unworkable. E-ink is also incapable of hitting the color spaces required by modern video content, and while colorful e-ink exists, it is a far cry from full color. E-ink is also far more expensive per pixel than the traditional RGB emissive. The energy consumption varies dramatically between the two technologies as well. While reflective displays use virtually no power during the day, they require massive amounts at night in the form of floodlights illuminating the otherwise unlit display surface. This is the opposite of emissive displays, which use a lot of energy in the day to compete with ambient light but require little at night to stand out in the darkness.
In closing, reflective displays are terrific in their specific applications, but for now they cannot really be considered substitutes for LED or other emissions – the technologies simply have different goals. While EPD solutions seek to be legible in high-bright environments, emissive displays seek to be high-bright in all environments. Over the next year we will continue evaluations and even building prototypes to expand the space to determine future applications. Anyway, with all that said, I remain fascinated by the technology and cannot wait to see where it goes!