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| The name “light-emitting diode screen” (LED-screen) itself is connected with the technology of information reproduction by displays of the given type. Light-emitting diodes are small semiconductors that emit light when connected in a circuit. They are used in screens’ production. |
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Light - emitting diode, LED is the semi-conductor chip that convert electric potential energy into electromagnetic energy. For each recombination of a negative and a positive charge, a quantum of electromagnetic energy is emitted in the form of a photon of light with a frequency characteristic of the semi-conductor material (in a semi conductor crystal with depletion zone, a junction or a contact called metal – semiconductor). In the LED when sufficient voltage is applied to the chip across the leads of the light-emitting diode, electrons can move easily across the junction between the positive and negative regions. When an electron moves sufficiently close to a positive charge in the positive region, the two charges “re-combine”. This recombination is accompanied by an optical radiation. Unlike thermal light source the LED emits incoherent radiation with a narrower spectrum. As a result consequence radiation in the visible part is perceived as a single-color one. Emission color related to the semiconductor material and its doping. A semiconductor crystal of the LED is usually shaped into a layer or a hemisphere. In order to improve characteristics of radiation’s direction the LED is placed into a parabolic or conic reflector.
Brightness of most LEDs is about 103 cd/m2, the best samples of light-emitting diodes have brightness up to 105 cd/m2.
Each light-emitting diode emits monochrome color of a certain wave-length – red, blue, green. For a full-color screen we use LEDs of all colours mentioned above.
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Pixel is a basic unit of programmable color. It is the smallest element in the LED display image. Each pixel consists of one or several light-emitting diodes. The amount of light-emitting diodes in a pixel depends on the pixel’s size and the supposed brightness of a display. In a full-color screen each is composed of one or several RGB (blue, green and red) light-emitting diodes. Due to the built-in processor we get all the basic colors and white color with its shades.
Pixels can vary from 4 to 40 mm in our model range.
- Dot Pitch is a physical distance between the centers of two adjacent pixels. The dot pitch specification for a display tells you how sharp the displayed image can be. The smaller the pitch is the higher the resolution is, as a result image’s quality is higher.
- LEDs per pixel: the amount and the arrangement of red, green and blue light-emitting diodes per pixel
- LED angle: a nominal characteristic of a light-emitting diode, established by its manufacturer, showing the maximal contrast ratio at which a light-emitting diode is visible with the sufficient brightness. When a viewer stays straight to the display, the brightness of an image is maximal. If the viewer is looking from other direction the brightness is weaker. The angle is measured when the brightness of an image is half the brightness of perpendicular viewing. The LED angle for video displays might be from 70 up to 140 degrees.
- Viewing angle: shows a real viewing angle at which the brightness of an image is half the brightness of perpendicular viewing. The viewing angle might be from 100 up to 160 degrees.
- LED clusters - emitting devices with some LEDs placed in a moisture-proof protected case. A cluster corresponds to an image pixel. The technology is used for manufacturing big outdoor displays of not a rectangular form or displays of a curvilinear form.
- Light-emitting diode modules (matrixes) - set of diodes on the surface of a display element. Here a pixel is not structurally arranged, but each LED belongs strictly to a certain pixel, and the operation of each separate pixel is carried out. It is used for a construction of big rectangular displays. In our model range we use the following dimensions of modules: minimal - 8 õ 8 pixels, maximal - 16 õ 32 pixels. The front-face module surface for outdoor usage has a moisture-proof filling.
Additional information: dimension –parameters of a geometrical figure. A line is one-dimensional, a surface (in particular, a plane or its part) is two-dimensional, space and also any limited parts of it are three-dimensional. With the development of the concept of multidimensional space geometry has started dealing with figures of any dimension.
- Cabinet. Modules (matrixes/clusters) are united in standard constructional elements – cabinets of different sizes, for example: 400õ400 mm, 600õ600 mm, 800õ800 mm, etc. Each cabinet contains a certain amount of pixels divisible by 8 and the size of a module with equal resolution (amount of pixels) can vary and it depends on dot pitch. A cabinet is a completed block for displaying graphic, video and alphanumeric information. It is supplied with a power unit and the required management devices. It is a base for the large screens’ construction. Modular construction allows building displays of any size, thus keeping their mobility and maintainability.
- Resolution is number of pixels per square meter.
- Screen resolution is number of pixels on a display. In our catalogues we specify in the following way: vertical resolution x horizontal resolution.
- Virtual resolution: here light-emitting diodes are not assigned to specific pixels. Program allows you to have an on-screen work area that is actually larger than your physical screen. Windows can extend beyond the screen's physical boundaries and are viewed by scrolling into the extended areas. When pixels are united both vertically and horizontally the amount of visible pixels doubles. It means that we get a picture of a very high quality as if we had four times more pixels.
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Viewing distance - the smaller the distance between pixels (and the smaller the size of a pixel itself) is the greater number of details can be distinguished on a unit of a display area and the closer the minimal point of supervision of a display is. It is caused by the fact that a human eye ceases to distinguish separate points of an image which are located on a distance of less than an angular minute. When the dot pitch (and the size of a pixel) is big it is necessary to increase the viewing distance for preserving the image quality because a light-emitting diode in fact is a point light source and as a result an image fragmentation reveals.
As a first approximation we prefer to consider that:
the minimal distance of a viewing distance is connected with
the size (dot pitch) of a pixel in the following ratio:
minimal distance (m) = dot pitch (mm)
The maximal viewing distance depends on the linear dimension of a screen, the bigger the liner dimensions are the bigger the depth and the area of the best perception of both text and video information are.
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