Headlights diming

i need help figuring out y my headlights and interior lights dim everytime i'm at the light and as soon as i start driving they get brighter....any suggestion are helpful.

when you are idling, your alternator puts out a lower current than when you are revving the engine. most cars do this, but it usually isn't a very significant differance. so it's not a big deal. how drastic is the change? if it's fairly serious, then i would take it to an autozone and an oriely's and have the alternator output tested. go to more than one place, because it's really easy for them to just tell you it's broke, and screw you into buying a new alternator ( $70 - $120 depending on vehicle).

normally it dims more when at night with the heating on and it gets a lot brighter as soon as i accelerate...i will look at it and take it to a place to check out the alternator...