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Innovative LED technology for DLP rear-projection cubes
In control rooms it is required to show information on a large surface in a high resolution, excellent image quality for 24 hours a day, 7 days a week, 365 days a year. Therefore a technology is required which fulfills these requirements. The optimum way of achieving this, is to use a matrix of modular DLP rear-projection cubes which are built up to a video wall and which are connected to a graphics controller. With such a solution you achieve a very high total resolution on a huge surface. Through a special design and by using special screens the image will even be seamless and have a very good viewing angle with a good brightness and a good contrast also in critical light environments. The other task to fulfill is the 24/7 operation with a safety to failure and an stability of the image in terms of brightness and colours. As we heard so far in these cubes High-Intensity Discharge (HID) or Xenon lamps were used, as they have a limited lifetime of only 500-10.000 hours, automatic dual lamp systems were available. These automatic dual lamp systems assured that if one lamp fails, the second lamp will take over.
As today the LED technology has made great strikes and the development of high-performance LEDs has moved forward dramatically, the LED technology is on the way to replace the old HID, UHP or Xenon lamp systems. As we will see the LED technology has not only a big advantage in terms of lifetime and therefore operating and maintenance costs but also for image stability and –quality. Especially when using the systems in continuous operation it is important to have an eye on the service and maintenance costs. These were quite high with normal HID/UHP/Xenon lamp systems as the lamp was considered as a consumable without warranty and also because of the necessity of re-adjustments of the system in terms of brightness and colours. The new LED lights are not considered as a consumable at eyevis, but as an electronic component and therefore are under the normal warranty. Also in the traditional lamp systems a colour wheel was used with a limited MTBF, which was also considered as a consumable. The MTBF given by the LED manufacturer is 60.000 hrs at 100% LED brightness, but as these LEDs are rarely operated in normal conditions at 100% this means that the MTBF can exceed this 60.000 hrs. With the new LED based DLP cubes the colours are created by three LEDs in red, green and blue, therefore a colour wheel is no longer required. Compared to the traditional lamp systems the operating and maintenance costs of LED lit DLP cubes is 70% lower. The colour adjustment with the HID/UHP/Xenon lamp system was a task for experienced users and required quite a long time to achieve a good result. Tthe High-intensity Discharge lamps contain mercury that makes them also difficult to dispose it and you will have to follow the rules of disposal for hazardous waste. LEDs don’t contain mercury and also as they have a higher lifetime this means less waste and lower usage of resources that means that this solution is more eco-friendly. But not only the higher lifetime, the reliability, colour and brightness stability, eco-friendliness, image quality, maintenance and service friendliness makes the LED DLP cubes an ideal solution for control rooms or other applications in continuous operation but also in broadcasting applications. The LEDs produce much less heat than the traditional lamps and also they don’t produce degrading UV radiation, which can damage the optical parts in the projection engine. In the traditional lamp cubes the colours are created by a colour wheel, this mechanical part is also considered as consumable and has to be replaced from time to time. As already mentioned in the LED lit engines three LEDs are use to create the colours, the LEDs produce faster the three primary colours but the fast switching time is not affecting the lifetime. Also by variation of the lighting period of each LED, the colour temperature can be much easier be adjusted. Another advantage of the LEDs is that if the system is switched on the LEDs are immediately bright, while normal projection lamps need to heat up until they achieve the full brightness.
Regarding brightness stability if we compare LED to lamps we can recognize that the lamps loose very fast their initial brightness and this already after a few hours of use they lose 20-30% of the brightness. LEDs work more constant, the red and blue LEDs loose only 20% of their brightness after 20.000 hours and the green one only 5%. At the eyevis test laboratory, a LED cube wall is running in a long-term test since one year an there was no change of brightness and colour. This stability is extremely important for video wall as all modules within a wall should have always the same brightness and colour to eliminate the chess board effect. Eyevis is the only manufacturer who has a real working multi cube automatic colour and brightness adjustment, with a communication of all the cubes within a video wall.
For display systems contrast, resolution, brightness and also colours are the most important factors to judge the image quality. You will find a lot of different values in the datasheets of the manufacturers and also some extreme high values, to boost their characteristics, but you will have to distinguish between marketing values and technical values. Also there are different ways to measure these values as well as there are also different test tools. The best way to compare the real image quality to see the systems next to each other in reality rather than only compare the technical data in the leaflets.
A fact is that the colour spectrum of LEDs is much higher than with traditional lamps. The bigger colour space allows the reproduction of more accurate and real colours. Each LED can be controlled separately, it is more easy to adjust a video wall and to use it also for broadcasting or TV applications, as also the colour temperature can be easily adjusted. By eliminating the colour wheel, the so-called rainbow effect of some manufacturers could also be eliminated, which could cause colour artifacts when moving the head or eyes quickly.
The light output and the temperature are determining the lifetime of the LEDs, that means that these two factors have to be controlled carefully. Therefore eyevis has integrated several temperature sensors as well as the colour and brightness sensors to get at every stage a reporting from the system about the status as well as being able to react quickly, automatically or manually. Also the cooling has to be very efficient, therefore eyevis uses a heat-pipe cooling.
Eyevis is so far the only manufacturer to have a very wide range of these LED cubes available, they range from XGA, SXGA+, HD to WUXGA, from 50” to 80”.
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