The LCD became the dominant color display technology in TVs, laptops, mobile phones, and signage for its light-weight, vivid-color features. As the imminent need to reduce carbon emissions is upon us, and the 2050 carbon-neutral target creeps closer, the color display industry needs to move toward a sustainable, low-emission display technology. So the color e-paper becomes the most environmentally-friendly alternative to LCD.

We share the differences between LCD and ChLCD e-paper, so you can choose the most energy-saving and sustainable color display.

How LCD works

An LCD is usually made of backlight, vertical and horizontal polarizers, color filters, and liquid crystals. The backlight module provides a light source to the display, the liquid crystals throttle the light passing through the two polarizers to create different grayscales. Then the color filters mix the light into different colors.

When R, G, B subpixels mix together perfectly, the LCD can reveal more than 16 million colors, creating vivid color displays in mobile phones, TVs and laptops.

How ChLCD color e-paper works

Cholesteric liquid crystal (ChLCD) e-paper has three layers of displays that reflect red, green, and blue respectively. The eletric field alters the rotation of the liquid crystals that is bistable between the two states:

The planar state has the liquid crystal particles lined up uniformly to reflect specific wavelengths of light, to form unique colors.
The focal conic state lines up the liquid crystal particles in a way to let light pass through, displaying the colors underneath.

ChLCD wavelength segment visible to the human eye — Altering the ChLCD particles on different layers to fully reflect light (white), partial reflection (gray), or no reflection (black).

A ChLCD can display more than 16 million colors, same as an LCD, by controlling the reflectance of RGB layers separately. So ChLCDs are as vibrant in color as LCD screens.

Advantages of LCD

The LCD technology has the following advantages:

The display's own backlight provides high contrast in a dim environment.
The fast response time means an LCD can refresh at greater than 60 Hz to play videos.

So LCDs are found in most consumer electronic screens, such as mobile phones, laptops, monitors and TVs.

Advantages of ChLCD color e-paper

Here are the advantages of ChLCD color e-paper:

The ChLCD is bistable in nature, so it only uses power during refreshes. It requires no power to maintain a static image.
Its reflective nature means the display contrast is greater in a brighter environment, which means the image is clearly visible under the sun.
The display does not have a light source, so it does not direct blue light into the eyes when viewing. It is safer for the eyes.
While most ambient light is reflected off ChLCD, about 10-30% of the light is absorbed by the bottom layer. So an embedded solar module at the bottom of ChLCD can generate renewable energy to create a zero-emission Infinity Display.

Infinity Display trichromatic light wavelength principle — Use solar cells to replace the backsheet of the ChLCD to generate electricity from ambient light.

Therefore, ChLCD e-paper is suitable for eye-friendly ebook readers and sustainable screens.

LCD vs e-paper in indoor color performance

LCD's backlight comes in handy indoors to provide high-contrast images, but it has trouble competing with the brightness of the sun outdoors. So LCDs usually look dim on a sunny day. Color e-paper reflects ambient light to form images, hence it looks brighter in a brighter environment, performing the best under the sun.

We use a light meter to calibrate different LED light sources and see the differences in visibility for LCD and color e-paper. We also set the iPad at the brightest setting for this experiment.

lcd vs e-paper image contrast under different led brightness — Image contrast of LCD and ChLCD e-paper with LED brightness from 1,000 lx to 10,000 lx.

LCD's images are more visible at low light (less than 5,000 lx) conditions, while the color e-paper looks better when reflecting a brighter LED light (greater than 5,000 lx).

LCD vs e-paper color performance in sunlight

When we place the two screens in direct sunlight, the window-facing setting (20,000 lx) and partially cloudly outdoor (75,000 lx), the iPad's backlight is overpowered by the sun, with hardly any visible detail.

lcd vs e-paper under different sunlight brightness — Image contrast of LCD and ChLCD e-paper with the sun's brightness from 20,000 lx to 75,000 lx.

On the other hand, the ChLCD screen excels at reflecting the sunlight to form vivid colors, making it an ideal technology for outdoor signage.

LCD vs e-paper in power consumption

Compared to a TV with 300 nits, an outdoor LCD usually needs more than 3,000 nits in brightness to be visible in the sun, so outdoor displays usually consume 3 times as much energy to operate as TVs. If a 55" outdoor display uses ChLCD instead, and refreshes an image every 5 minutes, the e-paper display only uses less than 1% of the LCD's rated power.

ChLCD vs signage consumption — Energy consumption between LCD and ChLCD e-paper.

Combining the above pros and cons, LCDs are more suitable for playing videos indoors, while ChLCD e-papers are better options for color ebook readers and outdoor energy-saving digital signage.

If you would like to know more about color e-paper applications, please get in touch with us.