The automatic light sensor triggers one of two modes in the lighting circuit: Headlights on, and headlights off.
When the headlights are off, the DIC and radio are set to full brightness, and the dimmer switch has no effect on them. The instrument lights may be on or off, but both of mine are off. There was a change made at some point to make them easier to see.
When the headlights are on, the DIC and radio are placed under control of the dimmer, but the maximum brightness they can be set to is about 50% of the daytime level. he instrument lights are on, and also controlled by the dimmer.
Sky NA 2007 Midnight Blue
Sky RL 2008 Carbon Flash - Naked