Behind the arylic is a transparent rear projection film which allows the display to remain transparent while being projected upon. We see this type of technology being implemented in bus stops windows, for displaying up to date bus routes and other relevant info.
The display uses 40 infrared LEDs, an infrared webcam, acrylic and image and finger blob processing software. Placed around 3 sides of the 10mm acrylic are the LEDs that face directly inwards. Frustrated total internal reflection (FTIR) is the phenomenon in which light inside of media remains reflecting upon the media until the index of refraction of another object in contact, in this case a finger, is presented , allowing the light to reflect off of the finger which creates a blob of light under it. To accomplish this effect a relatively thick acrylic sheet was required, and LEDs were faced inwards and pressed against a finely polished acrylic edge to allow for maximum light penetration.