Posted in education on January 31, 2017 4:57 pm EST

Drilling Down on Video Walls

Carefully choosing pixel pitch and managing heat and control will maximize an LED video wall's benefits.

Central Weslyan Church, Holland, Mich., courtesy of LynTec.


 

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TAGS: avl design, integration, led, power management, video, video walls,

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By Dan Daley

LED video walls are growing in popularity. While they’re still well behind conventional projection systems—the most popular type of video platform in houses of worship today, by far—and LCD video walls, which utilize banks of flat-panel displays to create nearly seamless images, LED video walls are growing in presence, in churches and elsewhere (been to Times Square lately?), thanks to steadily decreasing costs. Their upfront costs may still be higher than either projection or LCD, but their cost of ownership is ultimately lower, thanks to the elimination of lamp-replacement costs for projectors; the overall higher energy efficiency offered by diode illumination sources; the flexibility of configuration that LED walls offer over LCDs, because of lower overall weight that enables larger walls; and finally, more granular components that allow for a larger variety of form factors.

As an indication of the segment’s growth, an analysis released by Persistence Market Research in New York City states that just the LED outdoor billboard segment is expected to account for around a 46% share of the global outdoor LED installed market by the end of 2021. Indoor installations are expected to grow similarly. Futuresource Consulting representatives based in Hertfordshire, United Kingdom, report that while LCD technology with super-narrow bezels (SNB) will continue to dominate the video-wall market, “the arrival of narrow-pixel pitch (NPP) LED products is expected to cause significant disruption in the market.” In other words, get ready for brighter, more seamless large-scale video.

Pixel pitch is an esthetic choice—think of the difference between 720 and 1080, or 1080 and 4K resolution—but also of the physical location of the wall in relation to where viewers will be.

Resolving resolution

Like all AVL technologies, LED video walls have their own peculiarities that users need to be aware of to maximize their investments and benefits. The first decision users must make is the resolution of the displays. The tighter the pixel pitch (the center-to-center spacing between each LED, both vertical and horizontal, measured in millimeters), the finer the resolution of the overall images. Pixel pitch is an esthetic choice—think of the difference between 720 and 1080, or 1080 and 4K resolution—but also of the physical location of the wall in relation to where viewers will be.

“It’s crucial to choose the right pixel pitch for the environment,” stresses Nicholas Fazio, product manager for Christie Digital in Cypress, Calif. “The smaller the pixel pitch, the closer your minimum viewing distance can be. If you’re too close to a video panel with a high pitch, the images will look pixelated—you’ll be able to see the individual LEDs that make up the image rather than the image as a whole. The ability to project a good-looking, coherent image is a balance between pixel pitch and viewing distance.”

Fazio says an industry rule of thumb has been to allow one meter of viewing distance for every millimeter of pixel pitch. So, if a pixel pitch is 5.2 millimeters, the optimal minimum viewing distance is 5.2 meters, or about 17 feet. He adds that Christie uses a different benchmark, depending on the nature of the content intended for the video wall, of 2.5 meters per pixel, so that same pixel count would bring the optimal distance to 13 meters.

Fazio says he’s seeing most of the LED video-wall activity in houses of worship that have high ambient light conditions, and that have a number of services and other activities throughout the week. That’s where the fastest return on investment will occur. “Churches with very controlled-lighting environments will still derive a lot of benefit from conventional projection,” he says. “But as LED costs continue to decline, the benefits of them will start to make more sense to more and more churches.”

Those benefits include lower operating costs, not just from the elimination of projection lamps but also from lower power consumption. However, Fazio cautions, users need to carefully measure just how much power/illumination they really need in their spaces. “You don’t want to run it at 100% power, because that will shorten the lifespan of the LEDs,” he says. More typically, power levels between 35%-45% of maximum will produce sufficient brightness. On the other hand, power settings that are two low can cause bit depth to collapse, with anything other than the brightest elements in the content being lost in darkness. “Blues and blacks and grays start to look the same,” he says. “Power balance is critical to a good visual outcome.”

Dave Cook, production chief engineer at Willow Creek Community Church in South Barrington, Ill., says he’s able to operate successfully at even lower average power levels, closer to 25%, in the church’s larger venues, thanks to a complete lack of ambient light. On the other hand, in the one room of the four where LED video walls are installed that has skylights, it runs closer to 50%. “Power settings are really mostly dependent upon the amount of ambient light,” he says.

Hot stuff

Jeremiah Leiter, president of Live Sound Co., a Greater Washington, D.C., area AV integrator, says users need to be aware of heat generated by LED walls. While the diodes themselves are cool, their power supplies will generate heat, and each LED panel will have its own power supply, so the area behind the walls can get hot. Good air circulation around the back of the wall is thus important. Some manufacturers’ products allow power supplies and control systems to be racked away from the wall, which keeps heat away and heat-generating equipment able to be centrally located, which can make cooling it easier and more efficient. Leiter cites systems from Planar among these, which that company’s literature calls “distributed architecture.” “We can run control over Cat-6 cable and DC power directly to the power supplies and bundle it all to the [displays],” he explains.

Integrators say that LED implementation in churches tends to be conservative initially, with LED screens often used in conjunction with existing projection systems, with a midsized LED screen placed in the center and used for IMAG and other applications and projection screens flanking it, or vice versa, with two smaller LED displays on either side.

“The thing about the LED screens is that they have the potential to be reconfigured in any number of ways in the future,” says Leiter. “That’s something that we’re seeing take place regularly in the touring world. We’re not seeing that happen yet in churches, but the potential for it is there and I expect that we’ll see that taking place as people get more comfortable with using them. Our experience has been that what happens in touring eventually finds its way into the church later on.”

Willow Creek’s Dave Cooke acknowledges that the church’s first video wall, a 12-year-old Mitsubishi Diamond Vision (yes, the same brand you saw at MLB parks a decade or so ago) might seem ancient on the Moore’s Law scale, but he adds that it’s produced fewer maintenance issues than the Chinese-made Absen LED walls they’ve installed since. However, he concedes that those more recent installations do get moved and reconfigured on occasion, such as for holiday events, and in any case the costs for current LED products have decreased so much that they’re nearing parity with projection. But those maintenance issues underscore a lesson he says he’s learned, which is to install LEC video walls with an eye towards future maintenance needs.  continued >>

 

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