[muawiyah]

BTW, any study that says having your lights on during the daytime makes you more visible is seriously flawed. All it does is cause other folk's pupils to contract, thereby making you less visible to them, and cause you to have reduced contrast at the horizon.

This has been known since WWII.

[petercooper]

Studies show otherwise. So why do motorcyclists have them on all the time?

[Petronski]

Your logic is seriously flawed.

[Arthalion]

All it does is cause other folk's pupils to contract

Uh, no. Your pupils contract at night because they have fully opened in response to the original lowlight situation, and are easily overwhelmed by the relative brightness of oncoming (or in-mirror) headlights. During the day, however, your pupils have already contracted in response to the intense light thrown off by the sun. Unless that oncoming car has million candlepower bulbs, the headlights simply won't be bright enough to affect the eyes of anybody with vision good enough to drive anyway.

So should everyone have them on? Not necessarily. It's a proven fact that the human eye is extremely adept at identifying shiny objects. If you're cruising down the road on a nice, sunny day with a bright red truck with big chrome bumpers, it's a fair bet that you're visible and noticeable enough that nobody is going to miss you. If, however, you're driving your modern and chrome-less white compact car on a hazy afternoon, it's possible for some people to overlook your bland vehicle and possibly cause an accident...leaving your headlights on in that situation would make your car "shinier" to oncoming traffic, increasing your visibility and reducing your risk of accident. Since modern cars are increasingly chromeless and bland, features like daytime running lights are being added to make them stand out more in traffic (interestingly, my wifes new 2005 Dodge Caravan doesn't have this feature, and it's as bland as they get).

[RightthinkinAmerican]

Low beams will not cause your pupils to contract in the daytime. The sun is many times brighter, even on a cloudy day. Nighttime, yes.