Rear infrared configurations are used for effects where the participant will touch the screen. There are two possible configurations:
Rear lights. The IR lights are placed behind the screen. The advantage of this is simpler installation and it hides the lights. However, with some screen materials, there is too much reflection from the screen to permit this configuration.
Front lights. The IR lights are placed above and in front of the screen. This configuration is used when the reflectivity of the projection surface is too high to permit the use of rear IR.