The Indiana drivers' manual states "Drivers must use headlights between sunset and sunrise as well as at any other time in which visibility is less than 500 feet" (approximately 1/10 of a mile or 1 football field). The reason for using headlights in daylight is not for you to see better, but for others to see you better. You should turn on your headlights when:
Driving away from the setting or rising sun.
It's dusk or dawn - visibility is low and the angle of light makes it hard to distinguish shapes.
There's foggy conditions (use your low beams).
Driving in rain, as it camouflages shapes and decreases the ability of other drivers to see you.
Snowing - in darkened or stormy conditions, lights increase your visibility to help other drivers see you - especially in blowing snow.
So, if someone flashes their lights at you, they're just saying, "I can't see you well," and you should turn your headlights on - it makes it safer for everyone.
