daburned88,
my native language isn't english too! I try it anyway:
If you have a white matte screen (white wall, canvas..), the screen gain is about 1,0. Viewing angle is 180° , which means you can look at the projected image from all viewing points without loosing brightness.
If you have screen surfaces which reflect light more than a matte screen, you will have more direct reflections similar to a mirror. That means: angle of incidence = angle of output. Depending of the screen material this gives an increase of brightness within a limited area called viewing angle. Now the reflected brightness of a screen has more gain. There are gain screens from 1,2 up to 16. Screen gain is a ratio factor always compared to a 1,0 gain matte white surface. Most screen gains commonly range between 1,3 and 2,8.
Screens with more gain tend to 'hot spotting', which means some areas of the image are brighter than others. This depends of viewers position in the room in relation to projectors position.
Simple said: A gain screen cannot produce more brightness than a projector gives, but it can collimate the given brightness to the viewer, which now must sit in the view angle area.
Retrofeflective screens are directing light rays back to the lightsource (projector), the same principle like 'cat eyes' in road marking elements.
For more information you should look at 'Dalite' homepage.There must be somthing like 'educational', which gives an overview of all types of screens.
Good luck!
xblocker