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Vanish in windtunnel

Blow-Through LED?

Don't get fooled

The outdoor use of LED screens is still subject to myths and unawareness of possible risks. A persistent misunderstanding is the existence of blow-through LED panels. To cut things short, a transparent LED panel is not the same as a blow-through LED panel. Let's explain.

Any structure is subject to possible failure when not built and used according to the guidelines and design parameters set in each product's structural report and manual[i]. This also applies to LED screen support structures.

A guaranteed structurally sound structure needs to be designed, approved, build, inspected, checked, and maintained by a structural engineer or competent person. Except for unforeseen conditions outside the design scope, these pre-conditions will make it unlikely that the structure will fail. This also applies to temporary structures, such as roof structures or LED screens, as often used in the entertainment industry.

A large LED wall will behave like a massive sail in the wind. It's subject to wind loading or wind pressure. In this respect, a transparent LED screen should not be confused with wind permeability or "blow-through" LED. Are you still skeptical? Just go outside, hold a piece of gauze cloth in the wind and see what happens.

Wind permeability is a factor expressing the amount of wind that passes through an object.   

A transparent LED screen looks open, but the shape of components determines the aerodynamic behavior of the LED panel. The wind that passes the screen causes drag and increases the wind forces on the screen, lowering the permeability factor.

The picture below shows a car in a wind tunnel. It clearly shows the "drag" or "under pressure" indicated in blue at the vehicle's back. This force pulls the car back. The more aerodynamic the vehicle is, the lesser the drag. This same effect of under pressure or drag occurs for any item that is subject to wind force.

The picture below clearly shows this temporary roof structure is cladded with transparent scrim or gauze. You can still see the building behind it. What you also can see is that the wind force has a significant grip on the scrim. Also, here, transparency is not the same as wind permeable.

The wind permeability factor, in general, is expressed as Cf. This factor can only be determined for an object by wind tunnel testing or high-tech software.  Realtime testing in a wind tunnel gives the most accurate results.

Please note that objects and structures in the direct vicinity of an LED screen might affect the wind pressure to be addressed. These objects might lower the permeability factor. Your structural engineers can help you to determine this.

ROE Visual applied wind tunnel testing for the Vanish V8T LED panel.  Results show that you can consider a reduction of the wind force of 48%. These findings result in a calculation factor of Cf 0.81 for the V8T LED panel and Cf 1.57 for a fully closed panel of the same size.

Knowing this factor, we advise you to contact your staging company, rigging provider, or structural engineer during the design process of your outdoor structure at all times. Never underestimate the amount of forces at play.

ROE Visual performs structural analysis on all its products. These reports are available on request and will inform you about the wind pressure the LED screens can resist and additional measures that might need to be taken.

Read our whitepaper on the outdoor use of LED screens.

 

[i] Products without such documents (or where the manufacturer is not able to provide such documents) should not be trusted at all.

 

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