Display Technology
Specifying reliable display systems for outdoor use
By Tony Large, technical director, Crystal Display Systems Ltd T
he advantages of using industrial electronics in harsh environments is well known, however IP ratings and environmental challenges when using displays outdoors is somewhat of a quagmire of information. We see a lot of tenders for public projects, which have been written by consultants and mandate huge specifi cations for systems, that could well be unachievable within the project budget. For example, extremely high minimum brightness and unachievable contrast ratios. It is important to consider the real-world application for the displays, and the ultimate requirements of the display, to successfully complete its function. This article 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 an important factor when looking for a display system that will be used outdoors. However, not every display requires retina-piercing brightness to achieve its objective. For example, a display system used in a parking terminal does not require the same brightness of those used for digital signage.
More important is the contrast ratio, from the position of the user of the display. Achieving high contrast with a reduced brightness can create a better real-world viewing experience.
At CDS we have adopted optical bonding as our preferred method of creating a reliable system for use in this environment. The process of optical bonding is described in our capability document.
Outdoor displays need a cover lens to protect the thin-fi lm-transistor (TFT) from damage, therefore the benefi ts of optical bonding for outdoor displays are even more pronounced. By fi lling the space between the emissive TFT layer and the cover lens, you can benefi t from the following improvements. Higher contrast ratio, due to removal of light refraction within the stack
22 February 2024
Figure 1: CDS outdoor kiosk
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 condensation that can form behind cover glass during rapid temperature changes (such as a sunny winter’s morning) Environmentally friendly, as you can reduce the panel brightness
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 actively adjusts 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 a real-life reading of the work
Components in Electronics
around the display. Moving the light sensor to the bottom bezel avoids the shadow cast by the sun visor.
IP (Ingress projection) Rating for outdoor displays is an interesting area to consider, and a lot of this comes down to the capabilities of the client and the surround electronics required, along with the usage case. IP rating also infl uences the infi eld serviceability of the item.
The usage case should be considered from several aspects: Installation location - fully outdoor (direct/ semi outdoors)
Local climate (California vs Coventry) Interconnections between peripherals (connectors and locations)
High risk location (such as unmanned/ remote areas)
In fi eld service requirements
Cover lens choice is important in outdoor display. You should consider the surface
finish to reduce glare and reflection, as well as protect from the harmful rays of sunlight if required. You could also consider branding the cover glass with a custom colour pallet or client logo. For digital signage applications, we would always recommend our IP66K range as an out-of-the-box solution, with all the electronics (display, PC, player etc.) 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, where the latest high TNI panels are used and can withstand surface temperatures up to 110 °C. In the case where in field service is required, you could adopt an IP65 design which enables the system to be opened for service whilst in situ. These systems include pneumatic rams to aid single
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