Avoiding screen blotches
Under direct sunlight, the liquid crystals in a display will undergo ‘phase changes’ if there is a dramatic increase in the panel’s surface temperature. Black blotches will appear on the screen when this surface temperature reaches 60 C (140 F).
To prevent any such ‘solar blackening’ symptoms, outdoor digital signage systems should use in-plane-switch panels, which offer an internal temperature tolerance of 110 C (230 F). In addition, fans and blowers should be used to circulate the air and maintain the internal monitor temperature at a maximum of 60 C. This will facilitate the proper functioning of the electronic components inside the displays, including embedded computers, Universal Serial Bus (USB) modules and Analogue to Digital (AD) converters.
The right type of watertight
As mentioned, it is important to seal an outdoor display against exterior moisture, but this can also lead to an internal buildup of heat. To prevent too much heat from accumulating, one option is to use a ‘heat pipe’ and thermoelectric technology to transfer the interior heat to the exterior through an aluminum surface. This has proven effective in transflective LCDs.
In situations where more LED BLUs are deployed, however, there is a need for stronger measures for heat dissipation, such as ventilation systems that can blow air between the protective glass and the LCD panel, using input and output connectors that have been tested for ingress protection (IP). With the exception of air exhaust holes and strategic air inflow, the panels can still be completely and tightly sealed.
Myung Kune Moon is executive vice-president (EVP) of Nanov Display, which manufactures LCDs for indoor and outdoor digital signage networks. For more information, visit www.nanovdisplay.com.