The most widely used e-paper technologies today are electrophoretic display (EPD) and cholesteric liquid crystal display (ChLCD). Both are reflective displays that use ambient light instead of backlighting, making them comfortable to read even under direct sunlight.
Because both technologies are bistable, they only consume power when updating content and require almost no energy to maintain a static image. This makes them ideal for energy-efficient display applications such as retail signage, public information boards, and smart devices.
This article explains how EPD and ChLCD work, and compares their key differences so you can choose the right technology for your application.
What is an electrophoretic display (EPD)?
Electrophoretic display (EPD) is an e-paper technology that uses charged pigment particles suspended in fluid to form images.
Each pixel contains microcapsules (or similar structures) filled with particles carrying different electrical charges. When an electric field is applied, these particles move:
- Dark particles move to the top to form black pixels
- Light particles move to the top to form white pixels
This particle movement creates a stable, paper-like image with high contrast, which is why EPD is widely used in e-readers and electronic shelf labels.
A leading commercial implementation of this technology is provided by E Ink.
Color EPD
To display color, EPD systems use either color filters or multiple types of pigment particles. Recent technologies such as E Ink Spectra 6 have significantly improved color performance, enabling vivid colors suitable for digital signage.
However, color generation in EPD is still based on combinations of predefined pigments, which makes precise color control more complex compared to continuous color systems.
What is a cholesteric liquid crystal (ChLCD)?
ChLCD is a reflective display technology based on the unique helical structure of liquid crystal molecules.
It works by switching between two stable states using an electric field:
- Planar state: liquid crystal molecules are aligned to reflect specific wavelengths (colors)
- Focal conic state: molecules scatter light, appearing dark or transparent
In many implementations, three liquid crystal layers (red, green, and blue) are stacked together. By controlling each layer, the display can produce a wide range of colors through optical reflection.
Because color is generated by wavelength-selective reflection, ChLCD does not rely on traditional color filters.
Common features of EPD and ChLCD
Both technologies share several key advantages:
- Bistable operation
Power is only required during updates, and no energy is needed to maintain a static image - No backlight
Reduces power consumption and minimizes blue light exposure - Sunlight readability
Visibility improves under bright ambient light
These characteristics make both EPD and ChLCD well suited for low-power and outdoor display applications.
Advantages of EPD e-paper
EPD has been widely adopted due to its mature technology and strong performance in text-based applications:
- High contrast and readability
Deep blacks and bright whites make it ideal for text and documents - Paper-like viewing experience
Minimal glare and comfortable long-term reading - Wide viewing angle
Maintains readability from different angles - Mature ecosystem
Well-established supply chain and large-scale deployment across industries
Advantages of ChLCD e-paper
ChLCD offers distinct strengths, particularly in color and environmental adaptability:
- Strong color capability
RGB layer structures can produce a wide range of colors, suitable for image-rich content - Faster refresh behavior
Liquid crystal switching allows quicker updates compared to particle movement - Wide operating temperature range
Typically operates from around −20°C to 60–70°C, making it suitable for outdoor use - Reflective color performance
Maintains visibility and color clarity under ambient lighting
Color differences between EPD and ChLCD
Color is one of the main differences between the two technologies.
- EPD
Modern color EPD technologies, including Spectra-class displays, can produce vivid and visually impactful colors. These systems use multiple pigments to create a defined color range suitable for signage and retail applications. - ChLCD
ChLCD generates color through wavelength-selective reflection, which allows for a more continuous color representation in principle. This can result in a more natural color appearance under ambient light.
In practical applications such as digital signage, both technologies can deliver strong visual results, but they differ in how color is generated and controlled.
Speed differences between EPD and ChLCD
Another key difference is refresh speed.
- EPD
Image updates rely on the physical movement of particles, which takes time. Full-screen updates, especially in color displays, may take several seconds and can include visible transition effects. - ChLCD
Switching between liquid crystal states is generally faster, allowing shorter refresh times. While not designed for high-frame-rate video, it is more suitable for applications that require more frequent updates.
Deployment and system considerations
Both EPD and ChLCD support:
- Battery-powered operation
- Solar-powered systems
- Wireless connectivity
This makes both technologies suitable for distributed and off-grid deployments.
In practice, the differences lie in system design:
- EPD
Power consumption depends on update frequency and display type. Performance may also be affected in low-temperature environments. - ChLCD
Performance is generally stable across a wider temperature range, and system design is influenced by its optical and driving characteristics.
Overall, both technologies can be effectively deployed in low-power display systems, with differences mainly in optimization and environmental adaptation.
Which One Should You Choose?
Both EPD and ChLCD are important reflective display technologies, and in many cases their application areas overlap rather than strictly differ.
- EPD
Well established in applications such as e-readers and electronic shelf labels, and increasingly used in digital signage where high contrast, low power consumption, and mature ecosystem are key considerations. Modern color EPD technologies such as E Ink Spectra 6 have expanded its use into signage applications. - ChLCD
ChLCD is also applied in digital signage and information display systems, including scenarios where wider temperature tolerance, reflective color performance, and system-level design flexibility are important considerations. Depending on implementation, it can also be used in environments with more demanding operating conditions.
Rather than competing in separate application domains, EPD and ChLCD increasingly overlap in areas such as digital signage, while continuing to differ in underlying technology and system optimization approaches.
Conclusion
EPD and ChLCD represent two distinct approaches to reflective display technology. Both offer ultra-low power consumption, excellent readability, and flexible deployment options.
As color performance improves and new applications emerge, these technologies will continue to expand the role of e-paper across industries—from replacing printed materials to enabling more sustainable digital displays.