While the paraSOL weather system may control the climate of the Lunar Knights world, you can directly affect the intensity of Sunlight or Moonlight in the game by slotting one of the three Boktai games into your Nintendo DS's GBA slot.

When you start your game with Boktai slotted, you will be prompted to adjust the Solar Sensor. Afterwards, you will have one of three new items in your Valuables section of the pause menu. These three different Solar Sensors have different effects depending on which Boktai game is inserted in the GBA slot.

Solar Sensor Ver. 1
Insert "Boktai: The Sun is in Your Hand!" into the GBA slot of your DS.

Solar Sensor Ver. 2
Insert "Boktai 2: Solar Boy Django" into the GBA slot of your DS.

Solar Sensor Ver. 3
Insert "Shin Bokura no Taiyou: Gyakushuu no Sabata" into the GBA slot of your DS.