Optical system

A touch sensitive apparatus, comprising:

• a top plate having one or more light sources associated therewith, such that light from the one or more light sources is transmitted within the top plate with total internal reflection;
• and
• a base plate having one or more detectors associated therewith for detecting light transmitted within the base plate,
• wherein the top plate and the base plate are configured such that if an external body touches a first surface of the top plate, then light is coupled from a second surface of the top plate into the base plate through a first surface of the base plate;
• and
• wherein each of the one or more light sources is disposed within the top plate in a recess for that light source, wherein the recess has one or more refracting input faces such that light from a light source is coupled into the body of the top plate through the one or more refracting input faces.