The market for e-mobility displays has grown recently. The potential applications in this field require high demands on readability – the so-called sunlight readability of the displays – in different light conditions, such as direct sunlight.

Such displays must withstand very harsh environments. As a result, the display brightness must be significantly improved or the effect of the high ambient brightness must be reduced. Otherwise, the displayed images would appear washed out and especially the colour saturation would be completely lost. For classical displays in transmissive mode (e.g. TFT) or for self-illuminating ones (e.g. AMOLED), surface brightnesses of at least 2’000 nits (cd/m2) are required for good readability. However, displays with such a high brightness have significant disadvantages such as high energy consumption, burn-in effects, a limited lifetime and large power dissipations that lead to high temperatures.

Transflective display systems have been available on the market for some time. Older technologies achieve a reflectance of about 1 to 2 percent of the ambient light. However, these displays are no longer up to date in modern applications.

The latest display technologies achieve a reflectance of up to 16 percent. This produces high colour saturation and high contrast even under direct sunlight (Figure 1). With ECB (Electrically Controlled Birefringence) technology in combination with TN (Twisted Nematic) or IPS (In Plane Switching) technology, excellent contrast and colour values can be achieved under a wide range of conditions.

With ECB technology, two different display modes are realised within one LCD cell (Figure 2). The individual pixel is divided into two areas, a reflective and a transmissive part. This allows optimal design for different operating conditions, from direct sunlight to night-time operation. The division ratio between the reflective and transmissive areas can be controlled for customised displays, optimised to the application.

The transmissive part of the cell corresponds to the conventional TFT design with an RGB colour filter. The liquid crystal is arranged as in a TN cell. The light from the backlight is modulated by the cell. This results in a high colour saturation (NTSC: > 50 percent) and a high contrast of typ. 200:1 in this area (Figure 3).

In the transflective part of the cell, a metallic reflection layer is realised in combination with an optically modulated compensation layer in the form of microlenses. The ambient light passes through the beam path twice. In this way, good colour saturation values and contrasts are achieved. The integrated lens modulation guarantees good readability under different viewing angles.
Since the viewer always perceives the entire cell surface, the contrast and colour saturation values are average. They are generated from the two cell areas. This results in colour saturation values of typ. 6 percent in reflective mode and typ. 18 percent in transmissive mode. The contrast values also behave similarly: from 6:1 to 35:1.

Do you want a brilliant display for your eMobility application? As a display expert, we will be happy to advise you and show you the various possibilities. Contact us via email or submit your project enquiry directly via our display expertiser.

The market for e-mobility displays has grown recently. The potential applications in this field require high demands on readability – the so-called sunlight readability of the displays – in different light conditions, such as direct sunlight.

Such displays must withstand very harsh environments. As a result, the display brightness must be significantly improved or the effect of the high ambient brightness must be reduced. Otherwise, the displayed images would appear washed out and especially the colour saturation would be completely lost. For classical displays in transmissive mode (e.g. TFT) or for self-illuminating ones (e.g. AMOLED), surface brightnesses of at least 2’000 nits (cd/m2) are required for good readability. However, displays with such a high brightness have significant disadvantages such as high energy consumption, burn-in effects, a limited lifetime and large power dissipations that lead to high temperatures.

Transflective display systems have been available on the market for some time. Older technologies achieve a reflectance of about 1 to 2 percent of the ambient light. However, these displays are no longer up to date in modern applications.

The latest display technologies achieve a reflectance of up to 16 percent. This produces high colour saturation and high contrast even under direct sunlight (Figure 1). With ECB (Electrically Controlled Birefringence) technology in combination with TN (Twisted Nematic) or IPS (In Plane Switching) technology, excellent contrast and colour values can be achieved under a wide range of conditions.

With ECB technology, two different display modes are realised within one LCD cell (Figure 2). The individual pixel is divided into two areas, a reflective and a transmissive part. This allows optimal design for different operating conditions, from direct sunlight to night-time operation. The division ratio between the reflective and transmissive areas can be controlled for customised displays, optimised to the application.

The transmissive part of the cell corresponds to the conventional TFT design with an RGB colour filter. The liquid crystal is arranged as in a TN cell. The light from the backlight is modulated by the cell. This results in a high colour saturation (NTSC: > 50 percent) and a high contrast of typ. 200:1 in this area (Figure 3).

In the transflective part of the cell, a metallic reflection layer is realised in combination with an optically modulated compensation layer in the form of microlenses. The ambient light passes through the beam path twice. In this way, good colour saturation values and contrasts are achieved. The integrated lens modulation guarantees good readability under different viewing angles.
Since the viewer always perceives the entire cell surface, the contrast and colour saturation values are average. They are generated from the two cell areas. This results in colour saturation values of typ. 6 percent in reflective mode and typ. 18 percent in transmissive mode. The contrast values also behave similarly: from 6:1 to 35:1.

Do you want a brilliant display for your eMobility application? As a display expert, we will be happy to advise you and show you the various possibilities. Contact us via email or submit your project enquiry directly via our display expertiser.

Figure 1: Schematic structure of transflective displays

Read also:

Smart Embedded Displays
Low-Power Display-Solutions
What actually means "IPS"?

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