Turn on Headlights When it is Dark.
You must turn on your headlights when it is dark. This is sometimes defined as after sunset and before sunrise. More commonly you will see this defined as 30 minutes after sunset and 30 minutes before sunrise.
Why is it 30 minutes after sunset and not before? Wouldn’t it be more logical to turn on your headlights before sunset? I mean, isn’t it already dark immediately when the sun sets?
Actually, no. It isn’t dark just yet.
The period immediately after sunset is known as civil twilight. During this period the sky is still bright enough, even if you cannot see the sun. Streetlights are still off and you can see the road without using headlights.
This period will be roughly half an hour after sunset and half an hour before sunrise. This is why the half-hour is used in the law.
The real length of the twilight depends on your latitude and the time of the year. The higher the latitude, the more is the slope of the setting sun, and the longer it takes for the sun to reach 12 degrees beneath the horizon. When the sun is 12 degrees beneath the horizon most of us will say it is dark. At this point the sky is dark enough for some stars to be visible. This period is known as nautical twilight and you must turn on your headlights.
In the northern states twilight can last much longer than the half-hour, but the law still requires you to turn on headlights a half hour after sunset.
Before or After
Remember, it is 30 minutes AFTER sunset and 30 minutes BEFORE sunrise. This question may occur on your test.
When driving, however, there is nothing wrong in turning on your headlights long before the sunset and keep them on long after the sunrise. In many countries in Europe, the laws require you to keep your headlights on at all times.
This is not a bad idea.