With the VLC system described above, performance of the
USB module is measured. In the VLC system, the optical
power of the LED would be weaker and weaker with the
increase of the distance between the LED with the PD. To
restrain this attenuation, we put a lamp cup on the LED. This
cup reduces the diffusion angle of the transmitter LED to
gather the light and enable the PD receive more luminance. So,
the lamp cup can make contribute to the performance of this
system. In our experiment, We had tested the optical power of
the PD received with a cup on LED or not. The power of the
LED in this experiment is 300 mW. The power of the LED is
poorly controlled because the mobile phone in practice is a
low-power product.