reflected light beams are received by all light sensors 112 to generate light sensing signals thereon the strength of the light sensing signal decreases when the distance between the light sensor 112 and the pointer or the user 39 s finger increases the strength of the light sensing signal increases when the distance between the light sensor 112 and the pointer or the user 39 s finger decreases thus a distribution of light sensing signals can be obtained since the light emitters 110 and the light sensors 112 are arranged along y axis the light sensing signals are distributed along y axis and the y coordinate of the pointer or user 39 s finger can be obtained in fig2 the light sensor 112 closest to the pointer or user 39 s finger generates the light sensing signal with a highest strength and the signal strengths of the distribution of the light sensing signals gradually decrease from the center or peak toward two sides the distribution of the strengths of the light sensing signals shown in fig2 is generated by all light sensors 112 receiving the light beams emitted from the light emitter 110 closest to the pointer or user 39 s finger the distribution of the strengths of the light sensing signals generated by all light sensors 112 receiving the light beams emitted from other light emitter 110 will be different but the light sensor 112 closest to the pointer or user 39 s finger will generate the light sensing signal with a highest strength as shown in fig1 in.