The first protype headlight was invented in 1831 by Horatio Allen. Headlights were first used on trains in 1838 that would allow the observer to see 50 to 100 feet.
You should dim your headlights within 500 feet of the car in front of you. The rule of thumb is, if you can see another car, dim your lights.
If you can see the oncoming vehicle then he can see you. Dim your lights at that time.
If you can see his headlights, drop your high beams. In some states its the law 300 feet at least.
turn on your headlights
turn on your headlights
low beam headlights
until you can see both headlights in your side mirror.
Park your vehicle approximately 15 feet from your garage door or another wall. Open the hood and on top of both of the headlights you will see adjustment screws. Rotating them will lower/raise the headlights
500
If you are a courteous driver, you will dim them when you see their tail lights. No one likes bright lights in their mirrors, reflecting into their eyes.
It doesn't matter if your headlights are on if you can't see.