The operation of the DuoFern sun sensor is as follows.
When the sun is shining, the internal memory is charged and the "Sun start" command is sent when a certain voltage threshold is reached.
When there is shade, the internal memory is discharged again and "Sun end" is sent when the voltage falls below the threshold.
Accordingly, the sensor only works when the sun is shining. As soon as there is shade for 30 minutes, the sensor is completely discharged and no longer has any function.
Direct sun is ideal for charging. Charging then only takes about 10 minutes.
With indirect sun, it may take a relatively long time for the sensor to work.
When charging with artificial light, such as an LED lamp, charging may also take a relatively long time depending on the light source.