A faulty regulator on some models will cause the head lights to change intensity. The alternator needs to be replaced for this issue.Google+
Car Problem Reports
Honda Civic Faulty regulator may cause head lights to change intensity
Honda Civic Problem
Average Mileage: 148,798 mi (72,000 mi - 201,000 mi)
Visitor, 1998 Honda Civic, 122,000 mi
The head light intensity has varied on this car since I bought it. Have lived with it up to current time of 166,000 miles.
Visitor, 2006 Honda Civic, 72,000 mi
Head lights change intensity while driving.
Visitor, 1998 Honda Civic, 200,195 mi
Head lights will flicker as well as lights on dash, erratic , not all the time
Visitor, 1997 Honda Civic, 201,000 mi
headlight intensity varies