turn your headlights on...the button you use to dim you dash lights....push it in and bam super bright...then at night you push it again and they go back to where you had them set.
Looking at the dash, the button is located above the intersection of the center and left tunnels.
A funny sidestory - a friend of mine test drove a 1st gen 3 and couldn't get over how bright the gauges were. We pulled over and figured out that we just had to push in the button, but she was so put off by the experience that she went with an Impreza.
Funny, a magazine review of the 2010 M3 said the same thing I did: Dash lights too dim w/ HLs on in the daytime. Guess they couldn't figure it out either.