The D3 doesnt have a dimmer function to automatically change between day and night. I believe other AVICs have it but not the D3. I was pretty dissapointed to learn this. Maybe one of these guys knows a way to change it?
I have my dimmer set to around 30... i find that this is bright enough to be seen when its sunny out and dim enough not to bother your eyes at night. However its tough to watch movies at this level during the day so you have to constantly readjust. its a pain in the ass