Any application where a display system is located outdoors can be tough, and this is particularly true for the Electric Vehicle Charging Station market.
Devices get exposed to extremes of heat and cold as well as rainwater, dust, dirt, and grit. The display needs to be readable in bright sunlight or complete darkness and be strong enough to withstand external impacts from outside forces whether they be accidental or intentional.
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This combination of requirements is not unique to the Electric Vehicle Charging Station market, they are also a feature of most industrial display designs, so this extreme case contains lessons for everyone.
How to improve display readability for outdoor applications
The single best measure you can take to improve readability of a display in sunlight (or any other environment) is to ensure the display is equipped with a sufficiently bright backlight and use optical bonding between the cover glass and the display. Eliminating internal reflections between the different layers of the display by using glue that is indexed matched to the glass improves readability no end.
There are some drawbacks. For example: Increasing the brightness of the backlight, comes with a penalty: the backlight will draw more power and more heat in the display. Proper thermal management plays an important part here.
Why is thermal management important for EVC applications?
Thermal management needs to be carefully considered with a display that is likely to be exposed to the sun. Fitting an Infra-red filter protects the display from Infrared Radiation (IR) and prevents excessive heat build-up and its consequences, such as display damage or failure, but this can prove an expensive option.
Well-designed heatsinks for brightness enhanced backlight units are highly recommended where cost is a concern. Long exposure to Ultraviolet Radiation can also create undesired results in the finished product if not seriously taken into consideration in the early design stages. UV resistance materials offer long lasting protection against damage caused by Ultra Violet Radiation – such as discoloration and cracking to printed inks on the display coverlens, as well as disruption to the proper operation of semi-conductor devices used by displays and touchscreens.
An EVC or other outdoor system needs to be sealed to IP65, which precludes the use of forced cooling like fans, as well as the provision of apertures. The best solution is to fit a heat sink, though of course this will increase the size and weight of the system.
Choosing the right components to cope with maximum temperatures
The display components need to be specified to handle the anticipated maximum temperature. Two parts of a display that are particularly affected are the polarizers and the liquid crystal (LC) fluid itself. Standard polarizers have a temperature range of -20° to +70°C but extended temperature range solutions with -30° to +85°C are available.
And of course, the Liquid Crystal must be able to withstand the upper limit of the temperature range by ensuring that its clearing point is well within the limit of the displays maximum temperature range. Failing that will result in the screen turning black if the LCD clearing point is exceeded. This phenomenon reverses itself when you return to a cooler environment. Standard LC fluids have a ‘clearing point’ of around 80°C, but for displays where good operation in higher temperatures is required, materials with higher clearing points are available.
Strengthening the glass to prevent damage
For EVC stations, strengthened glass is a must. We have heard from customers that damage to displays is a constant issue. The units need to stand up to attempts of vandalism and accidental impacts from external forces, as well as cope with to not extremes in environmental conditions. Strengthened glass can be achieved using different methods to ensure it can perform still perform perfectly but stand up to whatever is thrown at it.
If your next project involves an integrated display, we would love to hear from you. Please get in touch to see if we can help.