Mine does the same thing. No it's not due to putting the headlites on. I imagine that the problem is similar to the clock light.I'm taking mine down for service next week and I'll see what the have to say. Probably a "cannot duplicate".
I have only noticed it on the "gear light" column. I will look for it on the clock. I do not get to drive it much but the next time I am in it I'll try this again . . . it seemed to be the opposite of a low voltage output problem. In other words, step on the gas it gets DIMMER not brighter as it would when the alternator output increases with increased r.p.m.
1996 Odyssey 120,000 miles
2002EX Odyssey w/towing package