When it comes to creating a large screen with almost no seams the rear-projection cubes are more than an interesting alternative to large displays. Their modular build-up allows an easy array to video-walls of any sizes. Most of these systems use a DLP Light-Engine. The common light source used to be a high pressure lamp that is used slightly modified in conventional projectors. At the ISE in February 2009 eyevis presented a system operating with high-end LEDs instead of high pressure lamps as a light source. The LED technology is promising some advantages like a very long lifetime and an improved colour presentation.
The LED projectors that have been presented on exhibitions so far were promising but had problems with the luminous flux. With the current state of technology the luminous flux for DLP- and LCD-projectors is not measureable. LED projectors used to be micro-portable devices with small image sizes and low brightness. At the ISE there have been many conversations in front of the new LED-Cube EC-50-LSXT+ that has been integrated into the walls of the booth. The visitors of the booth often stated that LEDs with current technology were not bright enough for professional operation like in rear-projection cubes. When the eyevis team told them that the wall next to them was made of LED Cubes this led to amazement under the visitors. This amazement tells its own tale, the LED cube impressed beneath the cubes with common lamps positively without attracting attention. The system makes the same standard impression like cubes with high pressure lamps just with the advantages of LED technology.
Talking about the technological data of the product the first figure to tell is the size of the rear-projection cube, the different screen sizes. These are available in the sizes 50", 67" and 70" in SXGA+, in 60" and 67" in Full-HD and with 70"-Screen with 1920x1200 pixels. This test has been conducted with a 50" device in SXGA+, this means with a native resolution of 1400x1050. The aspect ratio of the cube is 4:3 with a screen size of 100cm x 75cm, apart from 0,3mm boundary the whole screen is the image. The cubes are stackable and can be equipped with an optional scaler board making an external split controller unnecessary and allowing the array of video walls up to 10 x 10. The space consumption of the cubes is 62 cm this is more than large LC-Displays, but less and more compact than most rear-projection facilities. Without the optional scaler-board the EC-50-LSXT+ has a DVI-Input, the scaler-board provides further 2x RGB, 1x DVI (up to 1600x1200 pixels) 1x S-Video and 1x Composite-Video.
The handling of the cubes is normally not conducted directly at the cube, in general this works via a control pc with the eyevisCubeManager software. ISE is now 9 months back and already a lot of eyevis LED cubes have been installed all over the world.
Advantages of LED technology
The main reason for a displacement of the conventional high pressure lamps is the compared to LEDs shorter lifetime. Although the lamps in the rear projection cubes are not on the same power level like when they are in use in a projector, the lifetime is probably limited to a few 1000 hours. With continuous operation like in control rooms the operation time is 8766 a year, this is mostly longer than the operation time of a high pressure lamp. Consequently 2-3 lamp changes per year have to be taken into account, or you need a system with automatic double-lamp system in order to guarantee a continuous operation. In contrast a LED system is working for 55000 hours, this is an operation time of several years. Furthermore the LEDs can be turned on and off very fast without losing any product lifetime. A 1-chip-DLP-projector with LED light source therefore does not need any colour wheels like a normal projector. This is down to the fact that the light is almost achromatic and filtering is therefore not necessary. As a result the DLP-Engine is more efficient because the times when the segment borders of the colour wheel pass the DLP-chip do not have to be blanked so more light is available.
Furthermore an advantage of continuous operation with a LED-engine is that you do not have to recycle expensive and mercury containing high pressure lamps several times a year. A projection surface of 0,75m² has less requirements to the luminous flux of the projector than a 3 m² or more so the need for light is lower. This can be made clear in a rough calculation: If the screen of the rear-projection cube was a perfect diffuser, the relation between light on the screen and the resulting light density would be ?. With a light density of 370 cd/m² you would need a luminosity of about 1162 Lux (370 * 3,14 = 1161,8). For a screen size of 0,75m² this makes up a luminous flux of about 872 ANSI-Lumen.
Measurements
Colour measurements of the EC-50-LSXT+ revealed a high colour gamut. The primary colours are situated almost on the edge of the CIE-colour diagram, this means that the LEDs are very narrow and have an almost pure light. The very narrow light path contains most of the common colour gamut, including Adobe RGB as well as all gamut that are used in the production of film- and video material. With a certain calibration it is not a problem with the EC-50-LSXT+ to reach a replay that fits the gamut. The colour fidelity must fit for all cubes, not just for one, for the use of several cubes the colour and brightness need to be aligned. For this reason eyevis is offering special calibration possibilities respectively attendance and calibration as a service.
The light density measured at the EC-50-LSXT+ is 387cd/m², the fullscreen contrast is 1450:1. The angle-dependent measurement of the brightness shows that for a viewing angle of 35° the brightness is reduced by 50%, also in compliance with the specifications of the rear-projection screen that has been in use for the test.
Conclusion
With the new LED-rearprojection-cubes eyevis offers an innovation that is an interesting enrichment to the rear-projection market. The new systems are characterised as being easily capable to replace the former high pressure lamp based systems having no limitations concerning the brightness but in contrast a higher gamut and a longer lifetime of the light source.
The LED projectors that have been presented on exhibitions so far were promising but had problems with the luminous flux. With the current state of technology the luminous flux for DLP- and LCD-projectors is not measureable. LED projectors used to be micro-portable devices with small image sizes and low brightness. At the ISE there have been many conversations in front of the new LED-Cube EC-50-LSXT+ that has been integrated into the walls of the booth. The visitors of the booth often stated that LEDs with current technology were not bright enough for professional operation like in rear-projection cubes. When the eyevis team told them that the wall next to them was made of LED Cubes this led to amazement under the visitors. This amazement tells its own tale, the LED cube impressed beneath the cubes with common lamps positively without attracting attention. The system makes the same standard impression like cubes with high pressure lamps just with the advantages of LED technology.
Talking about the technological data of the product the first figure to tell is the size of the rear-projection cube, the different screen sizes. These are available in the sizes 50", 67" and 70" in SXGA+, in 60" and 67" in Full-HD and with 70"-Screen with 1920x1200 pixels. This test has been conducted with a 50" device in SXGA+, this means with a native resolution of 1400x1050. The aspect ratio of the cube is 4:3 with a screen size of 100cm x 75cm, apart from 0,3mm boundary the whole screen is the image. The cubes are stackable and can be equipped with an optional scaler board making an external split controller unnecessary and allowing the array of video walls up to 10 x 10. The space consumption of the cubes is 62 cm this is more than large LC-Displays, but less and more compact than most rear-projection facilities. Without the optional scaler-board the EC-50-LSXT+ has a DVI-Input, the scaler-board provides further 2x RGB, 1x DVI (up to 1600x1200 pixels) 1x S-Video and 1x Composite-Video.
The handling of the cubes is normally not conducted directly at the cube, in general this works via a control pc with the eyevisCubeManager software. ISE is now 9 months back and already a lot of eyevis LED cubes have been installed all over the world.
Advantages of LED technology
The main reason for a displacement of the conventional high pressure lamps is the compared to LEDs shorter lifetime. Although the lamps in the rear projection cubes are not on the same power level like when they are in use in a projector, the lifetime is probably limited to a few 1000 hours. With continuous operation like in control rooms the operation time is 8766 a year, this is mostly longer than the operation time of a high pressure lamp. Consequently 2-3 lamp changes per year have to be taken into account, or you need a system with automatic double-lamp system in order to guarantee a continuous operation. In contrast a LED system is working for 55000 hours, this is an operation time of several years. Furthermore the LEDs can be turned on and off very fast without losing any product lifetime. A 1-chip-DLP-projector with LED light source therefore does not need any colour wheels like a normal projector. This is down to the fact that the light is almost achromatic and filtering is therefore not necessary. As a result the DLP-Engine is more efficient because the times when the segment borders of the colour wheel pass the DLP-chip do not have to be blanked so more light is available.
Furthermore an advantage of continuous operation with a LED-engine is that you do not have to recycle expensive and mercury containing high pressure lamps several times a year. A projection surface of 0,75m² has less requirements to the luminous flux of the projector than a 3 m² or more so the need for light is lower. This can be made clear in a rough calculation: If the screen of the rear-projection cube was a perfect diffuser, the relation between light on the screen and the resulting light density would be ?. With a light density of 370 cd/m² you would need a luminosity of about 1162 Lux (370 * 3,14 = 1161,8). For a screen size of 0,75m² this makes up a luminous flux of about 872 ANSI-Lumen.
Measurements
Colour measurements of the EC-50-LSXT+ revealed a high colour gamut. The primary colours are situated almost on the edge of the CIE-colour diagram, this means that the LEDs are very narrow and have an almost pure light. The very narrow light path contains most of the common colour gamut, including Adobe RGB as well as all gamut that are used in the production of film- and video material. With a certain calibration it is not a problem with the EC-50-LSXT+ to reach a replay that fits the gamut. The colour fidelity must fit for all cubes, not just for one, for the use of several cubes the colour and brightness need to be aligned. For this reason eyevis is offering special calibration possibilities respectively attendance and calibration as a service.
The light density measured at the EC-50-LSXT+ is 387cd/m², the fullscreen contrast is 1450:1. The angle-dependent measurement of the brightness shows that for a viewing angle of 35° the brightness is reduced by 50%, also in compliance with the specifications of the rear-projection screen that has been in use for the test.
Conclusion
With the new LED-rearprojection-cubes eyevis offers an innovation that is an interesting enrichment to the rear-projection market. The new systems are characterised as being easily capable to replace the former high pressure lamp based systems having no limitations concerning the brightness but in contrast a higher gamut and a longer lifetime of the light source.
