Headlights should be turned on for night driving, during inclement weather, and during dawn and dusk when visibility is reduced. Some states also have laws that require use of headlights while running your windshield wipers, driving through a construction zone, or through a tunnel. It can be difficult to determine exactly what the laws concerning headlights are for each state. You may need to call your local police station, or check with the state's department of motor vehicles for official information.
Night driving is more dangerous because of greatly reduced visibility. Headlights should be turned on at night, as without them you cannot see or be seen. Normal range of headlights is about 350 feet. It is recommended that you slow down to a speed that allows you to react within that distance. Use of the bright setting increases the range, but you must turn headlights back to normal when within 500 feet of an approaching vehicle, and within 200 feet of vehicles in front of you.
The exact time to turn on your headlights as the sun rises and sets is not mandated. Use common sense and observe when other drivers start turning their headlights on. If you are having any difficulty seeing objects around you, then you should have your headlights on. Keep in mind that the shadows deepen at this time, making it very difficult to see pedestrians or other roadside objects to which you may need to react. Using your headlights at this time also makes it easier for others to see you.
Inclement weather is any weather condition that prevents a driver from being able to see a person or other motor vehicle clearly from a distance of about 1,000 feet. This includes rain, snow and fog. Many states have a law that requires the use of your headlights if the windshield wipers are running.
Some states, such as Pennsylvania, require the use of your headlights while driving through a construction zone. This increases your visibility to other drivers and to construction workers who may be driving construction vehicles out of unexpected areas onto the road.
As visibility is reduced in tunnels, headlight use is usually required, even if the tunnel has lights. Headlights help visibility because of the time needed to adjust to the abrupt change from dark to light for people entering and exiting tunnels, especially during daylight hours.
