Ensuring digital displays flourish in all conditions

Feature articles | June 2, 2014

By eeNews Europe

Displays & Interfaces

Below, we look at these challenges and the technologies to counter them. We then draw on AndersDX’s extensive experience with supplying UIs into widely varied applications to show these technologies working in practice.

Display enhancement requirements and solutions

Display enhancements are typically needed to accommodate and compensate for glare and sunlight, fingerprints and scratches, shock, vibration and malicious attack, and temperature extremes. Additionally, as displays become increasingly interactive, any enhancements must be complemented by suitable touch screen solutions. Other issues including humidity, water and dust ingress can be solved with suitable, and well-established, enclosure designs.

Circular Polarisers provide optimal sunlight readability, cutting total light reflections to 1% of incident light. Sunlight readability can also be improved by applying anti-reflection optical films or coatings combined with optically-clear glue between the display’s surface and the transparent protective layer. This can yield further reductions in total reflections to as low as 0.2%, resulting in a perceived increase in display contrast of some 300%. Anti-glare films reduce glare that can originate from over-head lighting, for example, by diffusing concentrated beams of light to levels far less distracting to the user, while increasing light output of a display’s backlight unit to deliver a front of display luminance of around 1000nits or above, which will greatly contribute to improved sunlight readability.

Optical bonding, the term that describes the clear-gluing process mentioned above, is highly effective in outdoor and public environments. As well as improving contrast ratios to 10:1, it provides up to three-times better impact resistance. Safety glass is also available to provide an excellent level of vandal resistance, while anti-smudge screens reduce everyday fingerprint and scratching issues. For applications such as ATMs where privacy is required, privacy filters are available that limit full-field viewing angles to 48˚ or 60˚.

Where strong sunlight creates heating as well as readability problems, a heat mirror can keep displays cool. By reflecting infrared radiation, these can reject 90% of incident solar energy. Conversely, a transparent heater can be used to warm displays in extremely cold environments, extending operating temperatures down to -50˚C.

Different touch technologies are available for interactive UIs. Resistive touchscreens are preferred where low cost and low emissions take precedence over ease of use. 4-wire types are standard, with 5, 6 and 10-wire solutions available as alternatives for enhanced robustness. They can be integrated with a coverlens for aesthetics and protection. PCAP Projected Capacitive touchscreens offer greater accuracy and an “iPad-like” user experience together with thinness, low weight, great durability, and multitouch capability. A recently-introduced technology – ShadowSense – offers a scalable and robust solution with drift-free performance, outstanding optical clarity and a fast, accurate response time. This optical touch technology, implementing multitouch detection from the periphery of the display, is reliable, durable and attractively-priced.

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Table 1 summarises the UI challenges and enhancement solutions available.

Challenge	Solution	Comment
Readability in bright sunlight and glare	Optical bonding	Contrast up to 10:1, 300% improvement in impact resistance
	Polariser	Cuts total light reflection to 1% of incident light
	Anti-reflection optical film	Increases contrast ratio up to 300%
	Anti-glare film	Improves contrast ratio, reduced surface reflections
	LED backlight	3 x increased light output
Impact resistance	Optical bonding	See above
	Safety glass	Excellent for vandal resistance
	Anti-smudge screens	Reduce fingerprints and scratches
Privacy	Privacy filter	Limits viewing angle to 48° or 60°
Overheating in strong sunlight	Heat mirror	Rejects up to 90% of incident solar energy
Extreme cold environment	Transparent heater	Extends operating temperature down to -50°C
Touch technologies	Resistive	Early technology, still highly favoured in industrial applications
	Projected capacitive	Provides good user experience, popularity accelerated by use in smart devices
	Shadowsense	More recent technology, highly accurate and cost-effective

Table 1

Real-world display enhancement examples

Because real-world applications are so diverse, finding the right UI products and engineering them into their target system takes innovation and flexibility. For example, an indoor environment is not necessarily benign; a recent UI project concerned a professional catering oven subject to the heat, humidity and rough handling of a busy kitchen. The oven’s designers wanted to achieve a competitive “iPad look and feel” for their product’s UI, without compromising their quality and durability requirements.

The engineered solution comprised a wide-temperature-range, wide-viewing-angle 10.1-in. TFT display with bonded Projected Capacitive touch screen. A custom 3mm-thick glass cover-lens provided the aesthetic finish together with industry-standard protection. The display is clearly visible under kitchen lighting with 400 nit brightness and 1024 x 800 resolution.

A real-time bus arrival display posed different challenges. This solar-powered device had to survive a wide temperature range while providing good visibility by both day and night. The appropriate solution in this case; Anders provided an extra-large custom 480 x 120 FFSTN wide-temperature, sunlight readable, negative mode display. Moving back indoors, Anders has supplied a 17-in. TFT for use within waterproof televisions for high humidity, wet areas. The television’s fixed mounting made wide viewing angles essential; the TFT provides these, together with high brightness, high contrast and an anti-mist system.

For business applications, simply providing a UI that can survive its environment is not enough. While overcoming the challenges of its particular application, it must make its host product competitive by being attractive and engaging to its users. To ensure both technical and commercial success, systems builders must source the best, most innovative display products, customised if necessary, and integrate them into a system providing appropriate environmental protection.

Mike Logan is Displays Product Manager at andersDX.