Electrophoretic display (EPD) is a paper-like, bi-stable, reflective low power technology that comes in both black & white (B/W) and colored formations. Behind everything is the electronic ink, whose reflectance (grey scale) can be controlled with voltage (16 levels). Resolution of modern EPD can be up to 300ppi. EPDs are outdoor-readable, perfectly suitable for static content with zero power consumption, yet allowing limited browsing capabilities. The refresh rates of EPD have recently increased drastically from 10Hz up to, reportedly, 60Hz. However, despite these developments, EPD still falls short in supporting high-speed video and gaming content. Perhaps the best-known application for an EPD is Amazon Kindle.
The most important property of the B/W EPD is the contrast ratio (CR). From a front lighting (F/L) point of view, the most important aspect is the ability of the system to maintain the CR when the F/L is switched on. This has a lot to do with the light extracting microstructures, their shape and replication accuracy. Any upward scattering light introduced by the frontlight operation will cause haze and decrease the CR. Nanocomp front light, with optimally engineered and perfectly replicated microstructures, offers superior CR levels for the frontlit display.
Color in EPDs is done either with color filters (additive color model), or with colored pigments (subtractive color model), the actual ink. With color filters, only the black and white ink are needed, which allows for the screen refresh rates to match those of the B/W version. When the colors are realized with ink, the sequential switching between the different colored states (e.g., CMYW) takes more time, but on the other hand, the colors are purer than with filters, and more individual colors can be achieved.
Most consumer products built on color EPDs are implemented with color filters to allow for the most versatile content and various media to be accessed with these devices. Since the filters are of a certain physical distance above the actual ink pixels, there can be leakage of incident light from one pixel to a neighboring one, which causes colors to mix and thus reduce in purity. This means a narrowed color gamut. To compensate for that, the incident light used to illuminate the display should be steep- and narrow angled. This can be implemented with Nanocomp frontlight, which indeed can enhance the color gamut of the display, if the F/L is kept operational whenever the display is in a state of dynamic use.
In addition to CR and color gamut, one more important aspect of Nanocomp technical excellence lies in the ability to control the color consistency (stable white balance) across the display area. In addition to the FLGP itself, the polymer materials used to stack up the display modules, including the sealing layers, touch panel, optical adhesives, and protective layer, tend to shift the color of light when it passes through them multiple times. This is especially the case for the front light sources (white LEDs), when they are coupled into the LGP on one edge of the display and then travel the full length of the display while interacting with these layers multiple times. Nanocomp UV replication material, onto which the microstructures are imprinted in the R2R process, can be precisely finetuned by special colorants to compensate for this color shift. This ensures that the frontlight supplied by Nanocomp always stands for the highest color performance and meets the customer´s specification, regardless of the display size.