Sign & Digital Graphics

December '14

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30 • December 2014 • S I G N & D I G I T A L G R A P H I C S ELECTRIC SIGNAGE development of AC LEDs and better heat management materials, the overall cost of LED lighting solutions will get lower and lower for both signage and general light- ing applications. It can be predicted that future LED lighting will have a similar cost as today's incandescent light source but, with more than 100,000 hours life- time," says Cao. Making and Measuring Consistency Reputable LED manufacturers and integrators have been able to provide color and output consistency with white LEDs, whereas six or seven years ago, consistency was a serious issue, according to Chris Smit, chief technology officer for US LED. An important part of creating consis- tency is in the binning process, where LEDs are measured and sorted and seg- regated by wavelength, range of flux values and the range of forward voltage. Basically, they're binned by brightness and output. "We do some binning techniques where we essentially sell a single bin of LED products to our customers," Smit says. "We also do special things with the phosphors and work closely with the LED chip manufacturers to ensure consistency from LED to LED. Color consistency was one of the problems with LEDs early on. Now you can say that is in the past." Like other LED companies, US LED is researching and developing better methods for sign cabinet lighting. Smit says the company is looking at both mechanical techniques and optics, such as different lens configurations, to maxi- mize LED light in a cabinet. "We're looking at various options, but at the end of the day in order to minimize installation costs you want to minimize how many modules you put in a sign. Stroke and depth is a focus in the indus- try," adds Smit. Fritz Meyne, Vice President Sales for Hackensack, New Jersey-based Bitro Group, is equally concerned with the point at which an LED is "born" on a sili- cone wafer, binned and delivered for use in an LED sign module. Meyne uses the term "efficacy" to describe the perfor- mance of an LED consistently over time, a term that describes the LED process from manufacturing to the final lighting application. "Efficacy is critical today to what that module will do today and consis- tently down the road. Overdriving a non-performing product to be as bright as a performing product works today and maybe tomorrow, but it won't be working well two years from now," says Meyne. "The proverbial, 'You get what you pay for' is just as true when buying LEDs as it is when buying a computer or a tire, so we continue to navigate to the more premium chip manufacturers. In com- mercial lighting if you have several LEDs that underperform, with a little differ- ent binning and color temperatures, it's less critical with those large commercial arrays than they are in a channel letter or cabinet sign." As noted earlier, binning or segregat- ing the LEDs properly plays an important role in their efficacy in the field. Binning has improved as demand has risen for LED lighting overall. Meyne says that demand now supports extra care at the point of manufacture. Those improvements, however, come with a caveat (or a caveat emptor, if you prefer)—there is no consistent test method to compare the brightness or efficacy of a given LED for sign applica- tions, according to Meyne. "The problem we have in the sign industry versus the lighting industry is that there are no testing specifications regarding performance. Company A may have tested it by putting a light meter right on the module while Company B may have tested it in an integrating sphere, which is how you should test it. Company C tests it in a 3" deep return, Company D in a 5" deep return. I cer- tainly don't believe any of the major play- ers are putting out erroneous informa- tion, so it comes down to the sign com- pany doing its own direct comparisons in a test letter," says Meyne. SDG Today's white LED lighting strands aimed at channel letter applications come in many different configurations. (Image courtesy of CAO Lighting) Today's LED modules often feature a curved lens that helps disperse the lighting evenly. (Images courtesy of Bitro Group)

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