As soon as you see a car directly in line towards you, you should go to low beam.
When the oncoming vehicle is within the reach of your brights.
As soon as the oncoming car is in sight.
500 meters
Use low beams.
I like to switch around 200-300 feet away from them
Bad low beam relay or dimmer switch
Be considerate in using your high beams. Your headlights must be on low beam when you are within 500 feet (150 m) of an approaching vehicle, or within 200 feet (60 m) of a vehicle ahead of you, even if the vehicle ahead is in a different lane. You should also dim your lights for pedestrians approaching you. http://www.nydmv.state.ny.us/dmanual/chapter10-manual.htm (Alaska and Oregon are the same as New York - 500 feet.)
low for a highway when theres many people around ...and if your on a dark road with no one on it use you high beams so youll be able to see better ...but remember on a crowded road having your high beams on can affect other drivers
check fuses, if good, possibly burnt bulbs or wires, check for voltage at wires.
Your low beams are burnt out. that happens alot
Bad dimmer switch.
Any car or truck regardless of make has the low beams on the outside. This is so you know where the outside edge of the car is as you aproach it at night
low beams my have burned out
Your high beams work but your low beams do not because the switch is broken that switches between high and low beams. Electrical switches wear out.