1999 Dodge Intrepid dimming & flickering lights

The lights on my Intrepid have become dimmer in the past couple of months and in last couple of days when driving at night I noticed they would brighten then dim back down again. The lights only brighten very briefly before dimming and there is no pattern to this. I'm not turning anything electric on or off and I am not accelerating or slowing down. I have checked the battery connections and checked for loose wiring, the belts and tensioner are new.