The size of the image is often determined by physical restrictions, such as ceiling height in the meeting room. Ideally the display size should be selected according to the amount of information required and the required viewing distance.
The more information within a given viewing distance, then the larger image that is required.
A single letter might be perceivable up to a distance which is 300-400 times the height of the letter.
Studies indicate that the minimum required character size must be > 16 arc minute, i.e. 16/60o. This implies that the maximum viewing distance equals 215 times the height of the character. That which the eye is capable of perceiving is also referred to as ‘acuity’.
DIN has a standard (reference 19045-1) which includes some guidelines for typical applications in meeting rooms. A viewing distance of 4 times the height of the image is recommended as providing the best information from an image. The viewing distance should not be less than 2 times the image height, and the maximum viewing distance not beyond 8 times the image height. But remember that the DIN standard was developed before PC-based presentations became the norm.
High resolution computer graphics require the closest viewing distance whereas video images can be perceived at a longer distance.
The next fundamentals are the viewing angles.