【Generation and Overcoming of Horizontal Bright Lines of Rear Projection Screen】Engineering Projection Screen Technology Introduction
Users who use rear projection screens may notice that a bright stripe is often produced in the horizontal direction of the screen, and its position changes with the observation height. So some users will wonder if this is a problem with the projector, or Is there a problem with the projection screen? In fact, the 'bright line' is not a problem with the quality of the equipment, but caused by the improper use of the projection screen. This line has nothing to do with the quality of the screen itself, and any structured screen may be produced. For example, the viewing distance is too close, or the optical path of the projector does not match the focal length of the Fresnel lens of the screen.
So, how did this bright line study come about? As shown in Figure 1, as the scattering angle increases, the vertical gain of the screen will drop rapidly.
The energy distribution in the vertical direction of each point on the screen is shown in Figure 1. The vertical viewing angle is very small. Therefore, if the viewing distance is too close (usually the viewing distance should be 3-6 times the screen height), as shown in Figure 2. , The scattering angle θ1 is greater than θ2, the brightness of point B observed at position 1 is much smaller than that of point B observed at position 2, while the brightness of point A observed at positions 1 and 2 is the same (because the observation angles are both Zero degrees), so the brightness difference between the edge point B and the center point A will be observed at position 1 and position 2. At position 1, the observer will feel that the center is very bright, so a horizontal bright line is generated. Naturally, the smaller the observation distance, the more obvious the bright line. The limit is that when the observation distance approaches zero, only one bright horizontal stripe can be seen.
Another situation is that when the optical path of the projector differs greatly from the focal length of the Fresnel lens of the screen, a serious mismatch will occur and bright lines will also be produced.
Now that we know the cause of the bright line, how should we overcome it? First, adjust the viewing distance: about 6 times the height of the screen, preferably no less than 4.5 times; second, use a projector that matches the focal length of the screen.