AFAIK it will not be as bright as when the lights turned off, this is because when it stays on with this brightness in the dark. You need to wear sunglasses 8).
I'm aware of the odo reset knob. I had it turn to the max. The thing is, the lights luminating the mileage dims whenever the headlights are switched on.
Is this normal? If yes, then I guess there's nothing to worry about then.