Video wall
As a video wall - or even a big screen, video wall, led wall, ledWall - refers to a large display area for displaying moving images.
Description
Find use video walls frequently during major events such as concerts or sporting events. In modern stadiums and large multipurpose arenas they have now become standard. Here, either a camera image or graphic information is displayed on the wall to present viewers a fan TV, commercials or statistical data for the action. It will be here in contrast to the film projector electronic signals recorded. Originally a video wall of only one screen or a matte screen on which an image was projected by a Eidophor. Often multiple CRT displays are assembled to form a large area, but whereby an interfering black grille originated from the interstices. Later projector were used to project, but wish the quality of low-light equipment left a lot.
Current video walls are mostly so-called LED Walls, that is, they form the image of lots of red, green and blue LEDs, so LEDs that are controlled by an electronic control system.
The following technical characteristics are a function of a video wall or the description of their properties. The image result arises from a complex interplay of these and other factors; depending on the application, the priority may be stored differently. So arise in the indoor use requirements other than for outdoor use - among other things is at indoor events the view distance is less, so that a finer resolution is beneficial. With exposure to sunlight in the outdoor area turn next to the all-weather capability are the brightness and the contrast behavior in the foreground.
Video walls are increasingly being used in advertising. So, in 2010, the largest test market in Saarbrücken Germany with a total of 8 video walls with a size of 9 to 15 square meters on main roads and at busy downtown streets. The test market has a total area of video wall modules of 84 m² (June 2011). The motifs usually change in 6 -second increments. The power of the network via a client-server solution with an Internet connection each video wall. The video walls can be adjusted within seconds the content, but also monitored remotely. A result of the crime series Tatort was turned off, including the video walls in Saarbrücken in May 2011.
LEDs
LEDs are superior to incandescent bulbs by low power consumption, long life and for the image display very suitable and controllable radiation. A maximum optical quality of a video wall can not be achieved without the highest quality in this component. For a homogeneous image also identical characteristics of all diodes used are important. In the long term is always an aging process to determine which manifests itself among other things in decreasing brightness.
Pixel
The smallest unit for the definition of a pixel is the pixel. Three LEDs in each case form a unit pixel. The more pixels there are, the higher the resulting image resolution of the video wall.
Virtual pixel
Using virtual pixels can achieve a comparatively fine image reproduction at a large pixel pitch: the software controller calculates the image on the basis of four diodes per pixel instead of three - with an additional red. As an intersection between adjacent pixels are created in this manner, additional - virtual, not physically existent - pixels.
Pixel Pitch
The physical resolution of video walls is derived from the pixel pitch, ie the distance from center to center of adjacent diodes. The values are currently moving about within a range of about 3 mm to 25 mm, with a smaller distance yields the finer, higher -resolution image.
Viewing distance
The perception of the pixel spacing is relative to the distance of the viewer to the image. As a rule of thumb that the pixel pitch, not applied in millimeters, but in meters, and the minimum viewing distance corresponds, from which the eye perceives a homogeneous image. 20 mm pixel pitch accordingly are around 20 m minimum viewing distance.
Viewing angle
For video walls in stages, the visual angle between 120 ° and 160 °. For viewers outside this viewing angle, the picture is no longer displayed optimally.
SMD
While conventional diodes are inserted with wires individually to the board, grasp SMD LEDs ( Surface Mounted Device ) Three diodes via surface mount soldered in a housing on a board together. The enabled with the SMD design smaller pixel pitch and high image quality are paying off where the viewing distance is small, ie primarily for indoor devices. Thanks to the rapid development in the field of brightness and durability SMDs find, however, also increasingly used outdoors.
Color depth
With color depth, the bandwidth is specified, can play in the individual pixel brightness levels of the basic colors of the RGB color space of red, green and blue. 8 bits per color call 256 levels, for a total of 16.8 million possible colors per pixel. The limit of the depth of color that can actually perceive the human brain, is from 6 to 8 bits. The significantly greater depth of color that is applied in the electronic imaging and playback ( currently 18 bits), the purpose of being able to adjust the image contrast dynamic to the ambient light is.
Frame rate
Fine color and greyscale transitions in moving pictures simulates a videowall very short image sequences. The processor controls the switching on and off of the individual diodes in time of nanoseconds, the man perceives as flowing course. The frame rate is given in units of hertz or megahertz ( Hz / MHz).
Brightness / brilliance
The luminance or brightness of an LED system is given in units of NIT. In the outdoor area some 5,000 NIT are common, are currently reaches up to 9,000 NIT. In Europe, instead of the unit NIT increasingly cd / m² (candela per square meter) common.
Manufacturing
The majority of all diodes and circuit boards is made in China, Japan, Korea and the United States. Also German and European supplier of video walls import these components and some of the entire video wall.
Assembly
Video walls are composed of modules and mounted in a housing. The individual elements included in addition to the LED boards, among other components such as fans that reduce the heat generated during operation development. The construction affects the suitability of the unit under extreme climatic conditions, the ease of maintenance and the life of the LEDs. A special problem arises in the effort to curb the electromagnetic radiation and to keep within the prescribed limits.
When installed in stadiums or arenas, the employees of a structural engineer is required and mounting in places of assembly subject to particularly strict safety regulations.
Mobile solutions
In addition to the video walls fixed portable devices, particularly in the rental business, offered to be fixed, for example, the crane or trusses. In addition, manufacturers offer specialized video walls that are integrated into show trucks with stage and media technology. On most compact are trailer video, so car or truck trailer including a video wall. Thanks a generator such installations in the daily use are mostly autonomously with respect to the power supply.
Legal requirements
An LED system generates electromagnetic fields and is therefore also a transmitter, so that in a more or less large area of radio communications may be affected. Video Walls and LED boards as electrical products are subject to supervision by the Federal Network Agency ( FNA ). This explains in one of her leaflets ( Federal Law Gazette 2008 Part I No. 6, issued at Bonn on 29 February 2008 ): "The Federal Network Agency is among other things for the execution and implementation of the Law on the electromagnetic compatibility of equipment ( EMC ) and the law on radio equipment and telecommunications transmission facilities ( R & TTE ) responsible. According to § 14 EMVG it is empowered to examine the market to be brought, put into circulation devices at random for compliance with the requirements of § 4 and § § 7-9 EMC. This applies equally to the requirements of the R & TTE. " Furthermore, make video walls usually structural properties in the sense of the building regulations of the respective states and thus is subject to both an authorization and restrictions arising from a variety of local statutes. Thus, for example, in the municipal area of any moving illuminated signs and thus the use of video walls not be approved. Even regular traffic regulations, here in particular § 33 " traffic disruption ", as well as emission control laws of the individual states should be adhered to in the planning stage stationary video walls.