The sensor uses a Hamamatsu S1133 silicon
photodiode. It produces a voltage which is
proportional to light intensity. The spectral response
approximates the response of the human eye as
shown in this diagram. The switch on the box is used
to select the range. If the reading from the sensor
reaches the maximum for the selected ranges, you
need to switch to a less sensitive range. If the reading
is very small or 0, you need to select a more sensitive range