thereby retaining full contrast and color saturation in the viewing  area. MATTE SCREENS.–  Matte  screens  diffuse  light evenly in all directions. Images on matte screens appear almost equally bright at any viewing angle. To avoid distortion caused by the viewing angle, the viewers should be no more than about 30 degrees from the center line of the projection axis; they should be no closer than two times the image height (2H) from the screen. LENTICULAR SCREENS.– Lenticular screens have a regular pattern of stripes, ribs, rectangles or diamond-shaped areas. The pattern is too small to be seen  at  viewing  distances  for  which  the  screen  is designated.  The  screen  surface  may  appear  to  be enameled,  pearlescent,  granular  metal  or  smooth  metal, and it may or may not have a coating over the reflective surface. By controlling the shape of the reflecting surfaces, lenticular screens can reflect nearly all the light from the projector  evenly  over  a  fan-shaped  area  about  70 degrees  wide  and  20  degrees  high.  People  seated  farther to the sides of the screen than the 70-degree angle or above or below the 20-degree angle may not see an image; no image-forming light is wasted outside the viewing area. Many lenticular screens provide an image three or four times as bright as a matte screen. BEADED SCREENS.– Beaded  screens  are  useful in  long,  narrow  rooms.  They  have  white  surfaces  with embedded or attached small, clear glass beads. Most of the  light  reaching  the  beads  is  reflected  toward  its source. Thus a beaded screen provides a very bright image for viewers seated near the projector beam. As a viewer  moves  away  from  the  beam,  the  image brightness decreases. At about 22 degrees from the center line of projection, the image brightness on a beaded screen is about the same as that on a matte screen. Beyond this angle it is less bright than on the matte screen. Since  nonimage,  or  stray  light,  is  also  reflected  in the general direction from which it comes, stray light falling on a beaded screen from a viewer’s position at the side of a room can be a major problem. REAR-PROJECTION  SCREENS.–  Rear-pro- jected images have the same requirements for image brightness, size and contrast as front-projected images. Rear projection has advantages in some situations and disadvantages  in  others. A person or object in front (on the viewer side) of a rear-projection  screen  does  not  interfere  with  the projection  beam.  This  makes  rear  projection  useful when the projector must be concealed, as in displays. It permits close examination of the screen image. Rear projection may provide advantages in image contrast and color saturation in a lighted room. Rear projection also has its disadvantages. With conventional projection, the space over the heads of viewers is usually used for the projector beam. With rear projection,  the  projection  beam  is  on  the  opposite  side of the screen from the viewers. Consequently, space for the beam must be provided outside the viewing room behind the screen. To reduce space requirements in rear projection, you should use short focal length lenses. More  commonly,  mirrors  are  used  to  “fold”  the projection beam. Both methods are likely to reduce image  brightness  and  quality. Another  important  consideration  in  rear-projection screens is the darkness of the screen as seen by reflected light. As with front projection, the highlight brightness of the image should be as bright or brighter than other areas within the viewer’s peripheral vision. If the image is to be viewed in a well-darkened room,  there  is  no  advantage  in  a  dark-toned  screen.  If the image is to be large, a light-toned screen is usually preferable  since  it  absorbs  less  image  light  than  a dark-toned   screen. You can achieve optimum viewing by using the following  accepted  standards  for  audience  placement  in relation to the screen, as shown in figure 6-9. Line of Vision In planning the space arrangement, the speaker should not stand in the line of vision. The lectern should be located to one side of the screen, leaving a clear view of two thirds of the stage area and only partially blocking the remaining third. On the opposite side of the screen from the lectern, A-frames, flipcharts, dry marker or chalkboards, and so forth, can be set up for optimum visibility. LIGHTING Proper lighting is Without  question,  the brilliant the image on important to relaxed viewing. less the room light, the more the  screen  and  the  greater  the contrast. On the other hand, brilliance and glare can be annoying  and  cause  eyestrain.  A  proper  level  of  room light  reduces  the  contrast  and  permits  viewing  with  a minimum  of  strain. 6-26