The D2-1(slave) has no switch or dimmer. It can be switched or dimmed via the D2-1 (master) or via the dimmer module LD200.
The D2-2( master) has a built in micro switch to dim the light or turn it off with the functionality to control the one or a group of LED D2-1 (slave). If required the light can be operated remotely an perform exactly the same functionality.
The D2-3  is used for night sailing or as a night light as it can  be switched from white to red or white to blue, the functionality on this light also means it can be dimmed on both the white or the colour.
The D1-3 (master) can be operated by the switch on the light or remotely from a switch on the bulkhead. It also has smart2 functionality, which means it can be operated via an app on a mobile or ipad.
These lights are all 10-30V multi-voltage and easy to install.