Sign & Digital Graphics

The 2015 LED & EMC Report

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Page 17 of 31

18 • June 2015 • L E D & E M C LED/EMC EMC Technology 35 mm, 20mm, 16mm, 12mm and 10mm—every manufacturer of full color LED displays (electronic mes- sage centers) loves to pitch its "pitch" when it comes to its products. The race is on as to which can be the next to offer the smallest number. Simply defined, pitch is the distance between the clusters of red, green and blue LEDs that make up a single pixel in a sign. The tighter the pitch (i.e., the smaller the number), the greater the resolution and image quality in a board. But the pixel pitch that some compa- Shedding Light on Pixel Sharing The facts behind the figures B y C h a d B o g a n Chad Bogan is the national sales manager for Adaptive Displays. nies offer actually uses a technique called "pixel sharing" to achieve a lower pitch in a "virtual" manner. Before you buy your LED display product, you should first understand more about pixel sharing and determine if this approach will work for your application. Virtual Reality "Virtual pixel" or pixel sharing—also called "virtual resolution"—is a prac- ticed method of getting the most out of an LED display array. While touted as a competitive advantage, pixel sharing does reduce the life of the display, and it can create color deterioration and detract from an image's clarity. Many manufac- turers are promoting this as an advantage and benefit. In its simplest form, pixel sharing or "virtual pixel sharing" is the process of digitally pulling an LED (red, green or blue) from another neighboring LED cluster and adding it to the primary LED cluster. Table 1 compares the pixel density for a virtual 16mm board with a real 20mm board. Although the virtual 16 mm board has 22 percent fewer LEDs, it seems to deliver a higher resolution. The initial impression that these figures seem to leave is that this type of board can effect a 16mm resolution with 22 percent fewer LEDs. At first glance, this seems like great news. From the manufacturer's point of view, this new product has 22 percent fewer LEDs compared to a true 20mm product and 50 percent fewer LEDs than a true 16mm product. This means that the product will cost about 50 percent less to manufacture than a true 16mm product, or 22 percent less than a true 20mm product. From the end user's point of view, getting a higher resolu- tion at a lower cost looks like a terrific bargain. But is this really the case? Weighing Your Choices First, consider the overall brightness. How can a product with half the LEDs be as bright as one with twice as many? The answer is that it can only be brighter if the LEDs are driven harder or kept on longer. Over-driving LEDs dramatically reduces product life and quickly deterio- rates the color and brightness. Second, if I have a static picture, how can I have an LED that is shared in four pixels operate correctly, or at four dis- crete levels? The answer is you can, only LEDs per square foot Table 1: This chart compares the pixel density of a "virtual" 16mm board with a real 20mm, 16mm and 7.8mm boards.

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