your alternator is going bad
you might have a short in your alternator. In my car the headlights would dim when I put on the brakes or tried to use cigerette lighter to power up my phone.
Remove the alternator and have it tested at any auto parts store?
Generally one of two things will cause headlights to dim; a power drain somewhere else (A/C compressor clutch, etc.) or a bad electrical connection. If the dash lights dim at the same time, it's most likely an electrical draw or short circuit. Don't automatically dismiss the A/C clutch because the A/C isn't on; some vehicles also run the A/C in defrost mode to dry the air.
Usually dim headlights are caused by a poor ground connection.
Check the grounds for the headlights.
could be the alternator is about to go out
Yes. Far as I know all cars do. They dim for night driving and may not be readable in the day time.
Yes, if you have dual beam lamps.
the courteous time to dim your headlights is as soon as you see another vehicle, or within one half mile.
when there are oncoming cars, it is appropriate to dim your headlights when they are about 300ft away. Check your diver manual for the most correct answer.
Your headlights may not dim because you don't have dimmer lights. Dimmer lights can blow and leave you with just the high beams.