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Advanced Imaging Magazine

Updated: January 12th, 2011 10:01 AM CDT

Doing Double Duty

Enhancing LCDs for industrial equipment with variable viewing angle control
Figure 1
© NEC LCD Technologies, Ltd.
Figure 1: A standard LCD module structure with an added viewing angle control component to the rear polarizer (shown in red).
Figure 2
© NEC LCD Technologies, Ltd.
Figure 2: In its "undriven" or natural state, light from the backlight is diffused and results in the widest viewing angle performance possible.
Figure 3
© NEC LCD Technologies, Ltd.
Figure 3: In the driven state, where an electrical signal is applied, the viewing angle control component will channel light from the backlight into a highly directional pattern and viewing angles will be greatly reduced.
Figure 4
© NEC LCD Technologies, Ltd.
Figure 4: The actual measured optical characteristics of an LCD module prototype that has electrically controlled viewing angles.
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By Robert Dunhouse, NEC Electronics America

The proliferation of publicly accessible electronic equipment with liquid crystal displays (LCDs) presents many challenges for the engineers who design them. More and more, these displays are required to support multiple roles. For example, the primary use of an automatic teller machine (ATM) is to convey sensitive customer or business information during interactive bank transactions. It also became apparent that, when not in use, ATMs could be used to present advertising or information to attract customers and ultimately encourage increased use. To be effective for dual purposes, there needed to be a technology that would limit the abilities of casual third-party observers to view customer-sensitive information.

Traditionally for these types of applications, security films such as 3M's Vikuiti™ display enhancement films have been applied to the LCDs, limiting side-to-side viewing angles. However, this approach fixed the reduced viewing angles and therefore was not ideal for distant, eye-catching advertising. Companies wanted to leverage the same equipment for both purposes—private and public.

Variable viewing angle control technologies address this dual-mode demand, enabling broad viewing of public information realized by a passive, wide-angle mode and secure viewing of personal information achieved by an active, narrow-angle mode.

Enhanced Displays

Electronically controlled viewing angle technologies offer dual-mode capability without requiring external films or additional peripherals. For example, NEC LCD Technologies has developed a unique "light channeling" technology that can alter the highly diffused or scattered light pattern of standard backlighting to a type that is highly directional. This technology is controlled through a single electrical signal and makes switching from wide to narrow viewing angles quick and easy.

Figure 1 illustrates a standard LCD module structure but adds a viewing angle control component to the rear polarizer (shown in red). Applying an electrical signal to this component alters the viewing angles. In its "undriven" or natural state, light from the backlight is diffused and results in the widest viewing angle performance possible (Figure 2). In this state, viewing angles are primarily determined by the optical design of the LCD module. Factors include the method in which the liquid crystal molecules are driven (standard twisted neumatic, in-plane switching, vertical alignment, etc.) and the characteristics of the polarizer film(s) used in the module. In the driven state, where an electrical signal is applied, the viewing angle control component will channel light from the backlight into a highly directional pattern and viewing angles will be greatly reduced (Figure 3). The narrow-viewing mode angles can be set as needed in the design stage. Figure 4 shows the actual measured optical characteristics of an LCD module prototype that has electrically controlled viewing angles. The designed viewing angle is reduced by approximately 50 percent.

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