A switch panel having a touch plate, image generator, imaging system and
light source is disclosed. The touch plate includes an optically
transparent layer having first and second surfaces in which a light
signal is trapped by internal reflection. The image generator displays an
image that includes a plurality of button positions to a person viewing
the touch plate from the first surface. When the user touches the front
surface at one of the button positions, light from a multi-LED light
source that generates the trapped light signal is caused to escape the
touch plate at a point corresponding to the point of contact. The light
leaving the touch plate is imaged by the imaging system and used to
determine the location of the point of contact. Images taken with
different LEDs in the light source are used to make the contact
determination to reduce the effects of ambient light.