Rear projection screen
The technology was temporarily used in televisions in order to achieve larger screen diagonals at low cost . It is comparable to classic video projectors , but in this case the projector is not in front of a screen, but is built into the device. Either a tube , DLP or LC projector is used to generate the image, which radiates the image upwards in the opposite direction. Above this is a trapezoidal plane mirror at an angle of approx. 45 degrees , which throws the light beam onto the translucent screen. A Fresnel lens arranged behind the screen ensures uniform brightness in the edge area of the display.
- They are often designed with almost no border and can therefore create picture areas of almost any size by combining several modules.
- In many areas of application (e.g. circuit diagrams of system controls) display quality and color fastness are not the main requirements. In these cases, the rear projection technology is more cost-effective than comparable TFT solutions, even for medium sizes .
- Large events: There is no beam path through the side of the audience, the time-consuming positioning and alignment of a projector is not necessary.
- They are insensitive to continuous operation.
- Very good readability even in very bright ambient light; no reflections in the image area.
- Significantly less lighting effect on the environment; large TFT systems act as an additional light source in the room.
- Low power consumption in relation to the display area.
- Very good contrasts and excellent black levels.
- Similar to the tube screen , the size of the display area always goes hand in hand with a certain construction depth.
- The service life of the lamps and the projector itself is limited. A quick exchange is possible in many cases, but these costs have to be taken into account when considering the TCO .
- The display quality of modern liquid crystal screens is achievable, but then at significantly higher costs.
Areas of application
Before the appearance of liquid crystal screens, rear projection screens in the consumer sector only played a significant role in high-quality entertainment electronics systems. At that time it was otherwise not possible to use the tube sets that were predominant at the time to create a screen size larger than approx. 85 cm. After the appearance of flat screens, rear projection screens cost significantly less than plasma televisions of the same size, but this changed quickly. In entertainment electronics, rear projection systems therefore play a subordinate role today and have been almost completely displaced in some areas.
However, rear projection systems were and are very often in use in system controls, control rooms, traffic control centers or major events and currently have no alternative there.