Think about the last time you were at a presentation where it was difficult to see the images being displayed. While there was nothing wrong with the presentation equipment or the quality of the installation, something was still not quite right. That something detracted from the presenter’s ability to communicate their message. When we are asked to look at spaces with this problem, we find it is almost always the size of the image on the projection screen. The ability to see the presenter and their material is critical for a successful presentation environment. This includes addressing the size of the image on the projection screen or monitor, proper viewing angles, and careful planning and design of the display location.
Image Size
The most common problem here is that the image is too small. The standard rule of thumb for sizing images is the four six eight (4-6-8) rule. This means the furthest viewer should be no more than 4, 6, or 8 times the image height away, depending on the material being viewed. Conversely, if you know the furthest viewer is 60 feet from the image then the screen should be 15, 10 or 7.5 feet high respectively based on the 4-6-8 rule.
The 4 factor is used when we need to inspect the image, such as a CAD drawing or a fine detailed map that requires close inspection. The 6 factor is used for reading or detailed viewing, such as spreadsheets or text with images. This is the most common size for presentation environments. The 8 factor is used for general viewing, watching a movie or images with few words. The 4-6-8 rule is derived from studies showing the minimum symbol height (i.e. text) the human eye can resolve along with a factor to account for viewers of varying visual acuity and varying viewing angles. No matter what the material, if you are doing a presentation, the 4-6-8 rule can be applied. Once the image height is known, the aspect ratio determines the screen width. There are many different aspect ratios for displays, the two most common aspect ratios we find are for video and HDTV. For traditional video displays, the aspect ratio is 4:3 (i.e. 4 units wide by 3 units high or 1.33); for HDTV displays, the aspect ratio is 16:9 (i.e. 16 units wide by 9 units high or 1.78). So the 10 foot high image mentioned earlier would be 13.3 feet wide for a traditional video display and 17.8 feet wide for an HDTV display.
Viewing Angle
The preferred viewing angle has the audience no more than 45 degrees to each side of the center of the image, or within a 90 degree “viewing cone” centered on the image. This cone can be expanded to 45 degrees off the edge of the image for acceptable viewing areas. Using the aspect ratio above, you now know the width of the image and can determine the acceptable viewing area. So between the 4-6-8 rule and the viewing cone we have established that the acceptable and preferred viewing areas in any room have a direct relationship to the size of the image.
Screen Location
We know how large the image should be but how big should the screen be? How high should it be off the floor? How far below the ceiling? Well, all of this depends on what or who may be blocking your view. If a short viewer can be seated behind a tall person, we have to either raise the screen, staggering the seating, or if in an auditorium, slope the floor. When you arrange the seats to create a greater distance between the viewer and the head directly in front of the viewer, you can lower the minimum height of the projection screen. Using a sectional drawing with tops of heads and eye locations drawn in (average top of head at four feet and eye at 3 feet 6 inches), you can quickly determine how high the projection screen needs to be off the floor to allow everyone a good view of the screen. In the end the solution will be a compromise, but we have found for most spaces the bottom of the screen is at 42 inches above the floor, and the top of the screen is no closer than 6 inches to the ceiling.
Ultimately there is no perfect solution to every presentation environment. But it is important to think about the presentation space and create a design that allows everyone to see and hear the presenter and their material with the least amount of difficulty. Combining a well-planned room with a good technical design equals a great presentation environment every time.