From BitWizard WIKI
The dimmer can be used to control the intensity of lights. It works the same as regular dimmers that can be bought in any other hardware shop, but can be controlled over I2C. It should work with any I2C-capable device, including the Raspberry Pi, Arduino and many other microcontrollers.
The dimmer can be found in the shop here
The dimmer is at I2C port 0x10. The value written can be between 0 and 255, where 0 is the lowest intensity and 255 is the highest intensity. With bw_tool it can be controlled like this:
bw_tool -I -w 10:XXX
Where XXX is the intensity