Specifying reliable display systems for outdoor use

Author : Tony Large | Technical Director | Crystal Display Systems (CDS)

01 March 2022

CDS_Outdoor Displays_optical bonding
CDS_Outdoor Displays_optical bonding

The advantages of using industrial electronics in harsh environments & demanding applications are perhaps well known & understood. However, the finer points of IP ratings & other environmental challenges when using displays outdoors can present something of a quagmire of information for engineers specifying such systems, says Tony Large, Technical Director at UK-based display solutions provider, Crystal Display Systems (CDS)…

This article was originally featured in the March 2022 issue of EPDT magazine [read the digital issue]. And sign up to receive your own copy each month.

CDS sees many tenders for public projects, often written by consultants and mandating very high specifications for systems, that could well be unachievable within the given project budget. For example, extremely high minimum brightness and unachievable contrast ratios. It is important to consider the real world application for the display, which will dictate the ultimate requirements of the display to successfully complete its function. Here, we will look at some of the aspects to consider when using a display in high brightness areas and public outdoor environments…

Brightness/contrast

Firstly, brightness is, of course, an important factor to consider when looking for a display system that will be used outdoors. However, not every display will require retina piercing brightness to achieve its primary objective. For example, a display system used in a functional parking terminal will simply not require the same brightness as those used for attention-grabbing digital signage.

More important, from the perspective of the display’s user, is the contrast ratio. Achieving high contrast with reduced brightness can create a better real world viewing experience.

IP66 Front
IP66 Front

From our experience here at CDS, we have adopted optical bonding as our preferred method of creating reliable systems for use in such environments. Outdoor displays need a cover lens to protect the TFT (thin-film-transistor) display from damage; therefore, the benefits of optical bonding for outdoor displays are even more pronounced.

By filling the space between the emissive TFT layer and the cover lens, you can benefit from the following improvements:

•  Higher contrast ratio, due to removal of light refraction within the stack

•  No possibility for dust ingression behind

•  Ruggedised display, as the bonding strengthens the stack, and supports the cover lens

•  Reduced greenhouse effect and solar gain (with suitable cover lens)

•  Removal of the air gap completely removes the risk of condensation that can form behind cover glass during rapid temperature changes (such as on a sunny winter’s morning)

•  Environmentally friendly, as you can reduce the panel brightness, using less energy

CDS_Outdoor Displays_transportation signage
CDS_Outdoor Displays_transportation signage

Above are some application examples of TFTs with (left) and without (right) bonding, showing the fogging that can occur in the air gap of the display and cover lens.

Another important consideration when using high brightness displays in public outdoor environments is to ensure you have automatic light adjustment, where required, so the display can actively adjust to the ambient conditions. This is not only important to ensure your display looks its best on a mid-summer’s day – but also to ensure it is not blinding its neighbours in the early hours!

Placement of the light sensor is critical to achieve an accurate real life reading of the environment around the display. In the previous example shown, the light sensor was moved to the bottom bezel, to avoid the shadow cast by the sun visor.

Weatherproofing

IP (ingress protection) rating for outdoor displays in another important area to consider, and a great deal of this comes down to the capabilities of the device and the surrounding electronics required, along with the individual usage case. IP rating will also influence the in-field serviceability of the item. The usage case should be considered from several aspects:

CDS_Outdoor Displays_display with embedded PC
CDS_Outdoor Displays_display with embedded PC

•  Installation location (fully outdoor vs semi outdoors)

•  Local climate (California vs Coventry!)

•  Interconnections between peripherals (connectors and locations)

•  High risk locations (such as unmanned or remote areas)

•  In-field service requirements

Cover lens choice is also important in outdoor displays. You should consider the surface finish to reduce glare and reflection, as well as to protect from the harmful rays of sunlight, if required. Branding the cover glass with a custom colour palate or client logo is a further consideration.

For digital signage applications, we would always recommend our IP66K range as an out of the box solution, with all the electronics (display, embedded PC, media player, and so on) in a completely enclosed system. These IP66 solutions are solid state and have no filters, and therefore require no ongoing maintenance, other than a good clean down every now and again. They are particularly well suited to areas of high dust concentration, such as railway stations (examples shown above). They use the latest high TNI panels and can withstand surface temperatures up to 110C.

CDS_Outdoor Displays_portrait display
CDS_Outdoor Displays_portrait display

In cases where in-field service is required, you could adopt an IP65 design, which enables the system to be opened for service in situ. These systems include pneumatic rams to aid single person maintenance, and are designed to maintain a constant and comfortable temperature. As such, they are suitable for street level use with touch screens. They can also incorporate water management, such as drain locations and run-off channels, upon opening the device for service.

For semi-outdoor, or integrated solutions, such as those built into street furniture (including kiosks), you can also adopt an IP65 front face display, which can be embedded into the side of your cabinet. These displays can include rubber sealing gaskets to maintain the IP rating of the complete enclosure.

This balances the cost and function of the system, offering a neat and simple way to integrate a display head into your design. The example below shows a 10” panel PC, with an IP65 front, custom aluminium bezel (with light sensor) and PCAP touch screen, tuned for rain exposure.

Aspect & orientation

It is also important to consider installation location. In the northern hemisphere, south facing displays are exposed to the longevity of the sun’s rays throughout the day, and need to be designed to cope with that. Operating temperatures need to be considered, dependent on the market and climate of the country of installation, to find the best product to fit the requirement. CDS can help here, and offer a customer-led consultation process to find the best solutions.

CDS_Outdoor Displays_bus stop
CDS_Outdoor Displays_bus stop

Many customers are also now using displays in portrait orientation to differentiate from traditional systems, and our IP66K models are designed to work in either format.

Through our customisation service, CDS can adapt standard designs for specific form factors, for example, in the case of limited headroom. Above is an example of an IP65 stretched panel PC, with incorporated 4G cellular connectivity module and ReACT (Receiver Antenna Compact Technology) antenna. This was designed as a replacement for a discontinued product, and enabled the customer to continue seamlessly supporting the end user service contract, extending the serviceable lifetime of the bus shelter.

Anti-vandal resistance  & monitoring

All outdoor displays need to be rugged; however, with some applications, this is more important than others. CDS can build systems that cater to your needs, and our IP66K range is designed to meet IK10 standard.

For those remote locations where vandalism can be a problem, we can also offer monitoring solutions to identify any problems with the system, including shock sensors, temperature sensors, backlight sensors, voltage monitoring and flood alerts.

CDS_testing chamber
CDS_testing chamber

We offer many off the shelf display systems, but can also design systems to meet almost all requirements presented to us. We can even install customers’ proprietary electronics into our systems if needed, which makes software integration much simpler. These can include 4G routers, fibre converters, monitoring boards, ReACT modules, and so on.

Testing & approvals

CDS takes pride in using only tested and approved products from our list of partners, having worked in the industry for many years. The experience we have gained has been invaluable in helping our customers achieve the best total cost of ownership (TCO) for their projects.

In-house sample soak testing (otherwise known as endurance, capacity or longevity testing) is achieved through independent environmental testing, using our state-of-the-art climate chamber to emulate outdoor conditions. This can test down to -40C and up to 180C!

Conclusion

In summary, there are a myriad of factors to consider when specifying display systems for outdoor use. By offering the right expertise and support, CDS can  help you to find the best, most suitable system that successfully meets both the expectations and requirements of your project, as well as your customer’s budget for the programme.


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