First off you must have the "PixController Universal V3"
board. This board started shipping in October of 2004. The previous
version of the Universal board did not have the POT to adjust the
light detection level for the day/night sensor. If you look on the
back of your board the V3 will be marked "PixController
Universal V3" on the upper left hand corner as show below.
The Day/Night sensor is located on the front of the board near the
PIR sensor (as shown below). This sensor is used to detect light
levels between day and night. This is used to run your board in
either day only mode, or night only mode. The day/night sensor will
sense light through the PIR lens.
Adjusting the light detection level
On the rear of your board is a small POT (R24), which is used to
adjust the light detection level of the day/night sensor. This is
mostly used to adjust when the external light port will be active at
night. If you turn the POT towards the "LT", or the left,
the external light port will turn on in darker conditions. If you
turn the POT towards the "DK", or right, the external
light port will be active in lighter (night) conditions.