Could be your headlights turning on. When they turn on the dash lights go to their night-time setting, which is much dimmer than the daytime. You'll notice it happening more during the winter months with the time changes and shorter day, you're driving at dawn/dusk more often. Next time it happens, check if your headlights are on. If they are, the best thing you can do is to turn up the brightness dial to the right of your headlight knob.
PS. Turning the auto-headlights off does NOT bring the interior lights back to their daytime brightness. Very frustrating.