Sign & Digital Graphics

November '17

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S I G N & D I G I T A L G R A P H I C S • November 2017 • 19 Harrison, vice president of the Foster Transformer Company. He explains that LEDs' forward voltage drop must be overcome before it conducts. "Once this threshold is crossed, the LED begins to conduct and emit light. As current begins to flow through the LED, it warms, and as it warms, the resistance drops causing more current to flow, which causes the resistance to drop further leading to what is termed thermal runaway. If the cur- rent is not regulated to a safe value, the LED will burn out and this is where the driver comes into play. An LED driver is designed to regulate both output voltage and current to safe levels." With this definition of how an LED driver performs, we can look at the ben- efits that come into play. At the top of the list is the fact that LEDs' low volt- age brings forth qualities that are not present in other lighted sign options. According to Bryan Vincent, a partner at Principal LED, "Low voltage reduces shock hazard during installation, reduces the amount of UL testing that is required (<15V DC is considered inherently safe by UL standards), and the driver can have built-in surge protection to pro- tect the LEDs in the event of a lightning strike or power surge." These are widely accepted benefits of LED configurations, and Meyne expands on the pluses of the driver. "The other function of an LED power supply is that it contains circuitry that limits the current output to a maximum of 5A; as well as having short-circuit protection/current limiting function," he explains. "All of this is so that the power supply can be classified as a UL Class and be safely usable for low-voltage LED installations. The Class 2 designa- tion also allows sign installers and fab- ricators to work with the secondary side products (and not just electricians)." Of course, with advantages also come potential setbacks. With all types of LED-based electric signs, there is a heat element involved. There are also ways for external environmental entities to impact performance. "Overheating and water damage (are) two of the biggest causes of premature failure," states Harrison. "Following manufacturer recommendations is the best protection. Retrofitting LEDs to existing fixtures without adequate ven- tilation can lead to overheating and failure. Both the LEDs and drivers can be weather-sealed, but if there is insuf- ficient space or ventilation to dissipate the heat buildup, problems will ensue. Manufacturers go to great lengths to identify proper installation procedures that should be scrupulously followed to avoid problems." And one manufacturer, Principal LED, suggests that even the mount- ing of the sign can lead to problems if approached incorrectly. "If the drivers and wiring are in the bottom of the sign and there is poor drainage, this can result in the power supplies shorting out," says Vincent. "If the drivers are going to be placed inside the sign, I recommend mounting them on the vertical side of the sign with access through a hatch or door. An even better option is to mount the power supplies inside an enclosure box at the base of the pole." In the same vein, Meyne is surprised that LED signage is continuing to be improperly installed given the sensitiv- ity that is associated with failure due to environmental elements. LED drivers have many benefits including supplying the low voltage requirements and built-in surge protection. (Image courtesy of Principal LED)

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