To Dim the Headlights or Not to Dim: What's in It for Me?

A reader named Linda Cass asks an interesting question that pokes into the self-interest/fairness/altruism area we’ve been writing about lately:

I’m an Englishwoman living in France but I should think the system of dipping one’s headlights for an oncoming vehicle is pretty much common in the U.S. as well.

I keep wondering why so few people fail to do this. There is no incentive to do this except for joining in the habit and hoping that everyone coming towards you does it too. There is no punishment if you don’t do it — I can’t really see a police car doing a U-turn and chasing you.

So why do 99% of people do it?

Let’s assume that Linda is correct, that the vast majority of drivers (if not quite 99%) do dim their brights. I do not have the world’s best nighttime vision, despite a lifetime of heavy carrot intake. (According to, the carrot/vision belief is pure myth, but a fantastically interesting one, derived from a British military lie during World War II meant to cover up the use of radar to intercept German planes.) So when I drive at night, especially on an unfamiliar road during the rain, e.g., there’s nothing I’d rather do than not dim my lights. And yet I do. Why?

Am I worried the oncoming car is a police car that will make a U-turn? Am I trying to avoid the little burst of shame that arrives when the oncoming driver flicks his brights at me? And if so, isn’t it amazing that a social convention like this one can survive on such a fragile sentiment?

The fact is that driving at night is dangerous. (If you ask Google to find you “nighttime auto accidents,” you’ll get lots of injury legal firms; but if you ask Google Scholar, you’ll learn about the proliferation of drunks, car thieves, and drag racers at night.) What I’d like to know is whether the benefit of dimming your headlights – that is, the benefit of not blinding the oncoming driver – is indeed larger than the benefit of keeping your own brights burning?

Tim Miller

The #1 reason I dim my headlights: High beams can blind the other driver - if you blind them, they cannot see where they are going, and they can drive head-on into you. Not my idea of a leisurely evening drive...


when you dim your lights, the oncoming car usually dims its lights in response.

Dim Bulb

The Golden Rule.


I think it's simply a matter of courtesy. When someone is coming toward you with their high beams on, it's almost blinding sometimes. It's also a requirement (at least I think it still is) in the driver handbook, to dim your brights - 100' if behind, 200' if oncoming.

Dim bulb in the distance.

I'm not sure that having your brights on in a heavy rain is the best way to see further ahead, but I dim my lights because I know that on undivided highways, common in Canada, everybody is safer if both drivers can see more clearly.

chris markl

You dim your lights because the costs are extremely low, clicking a lever for .2 seconds. Come on, the idea that people only act in their own self interest is limited thinking. When the costs are insanely low to help another, we just do it.


One possible result is not that the other driver flicks the lights, but just turns them on and blind you until you dim yours. At least that's something I do whenever the other driver does not dim them. Therefore, I think that it's not true that there are no consequences, there can be immediate consequences for your driving.


Like opening a door for someone behind you (which slows you down and costs you effort), slowing to let someone take a left across your lane of traffic, dimming your lights is an act of altruism.

And as with most other altruistic acts, the actor gets a 'good feeling' from doing something nice for a stranger, and, perhaps, a little optimism that their action will influence others to be similarly kind.


I think Tim nailed it. High beams are blinding. I don't want a blinded driver coming at me at 70 mph. That they do the same for me is a nice benefit.


The combined light from your headlights and the headlights of the oncoming driver is bright enough that you don't need your high-beams on for those few seconds.


In Florida, there is a law that requires drivers to dim their headlights to traffic, be it oncoming or in the same direction.

Eileen M. Wyatt

Does the Prisoner's Dilemma or similar apply?

If neither party dims, we're both blinded, and that's bad.

If both parties dim, we can both see, and that's good.

If one party dims and the other doesn't, eventually those who dim will get peeved at being blinded and stop dimming, leading to the situation in which neither party dims.

With this reward system, selfishness is, in the long run, counterproductive because it leads to becoming the victim of selfishness.

Joan Johnson

I agree that dimming one's headlights is motivated by self-interest. If I dim my headlights when a car approaches from the opposite direction, I enable that driver to see better, making it less likely that he will crash into me. AND, if I dim, he likely will dim too, also making it less likely that I will crash.


Being polite was much more common decades ago (or even longer ago) than it is now. However, there are small habits and customs that remain throughout time, such as dimming the headlights whenever we see approaching vehicles. Doing so requires minimal effort and movement; what it costs us to do it is minimal, and the time it takes us to do it is so small that it probably won't affect the time we have left for other activities throughout the day, which is why people still do it. It also seems as if the benefits of feeling satisfied, appreciated by others, and happy with ourselves all outweigh the small time it takes us to actually do the task.
In the Dominican Republic it is actually very hard to find people who actually do this. This annoyance, however, can lead to two different results. Either the person in the other car becomes angry and decides no to put the effort into dimming the lights, or he or she takes the high road, dimming the light so others can appreciate it and follow the example. It all comes down to moral and decision-making, as does everything in life. When making these decisions, people are presented with different events that can result from what they do, and we sometimes fail to make the right decisions because we're most inclined towards acting in rational self-interest, being either to remain comfortable in their seats or to do good to others so the goodness is carried on.



We're worried that if we blind the oncoming car with our brights, he or she will be slightly more likely to crash into us (or, more likely, clip us with a rear-view mirror while passing by), due to decreased depth perception and increased disorientation from the blindingly bright lights.

Yes, our own field of vision might be cut short without the brights, but we can take precautionary actions like slowing down. We can't control how safely the oncoming car proceeds.

It's the same age-old preference for feeling like we're in control of our destiny (the same reason plane crashes are bigger news than auto deaths). We're always more fearful of being the victim, as opposed to the cause, of a freak accident.


I avoid this problem by never driving with my brights on. Granted, if I'm on a remote road in the Southwest or Midwest, where in a lot of places you can see for miles ahead and there's not another vehicle in sight, it's brights away.

What really irritates and aggrivates me is that the vast majority of people seem to drive in cities/towns with their brights on. Come on...with the amount of streetlights and ambient light from buildings, billboards, etc you practically don't need headlights at all to drive at night in a city, so why leave your brights on?

Mike B

I think its because most drivers hate being blinded by the other guy so much that they feel a great deal of empathy when faced with blinding others that they simply don't do it. Remember that humans are wired to feel things like empathy and remorse. We don't go around stabbing people to death simply because of criminal penalties, but because such actions make us feel bad.

Because we all experience the negative costs associated with being blinded we can empathize with those we might be tempted to blind. Moreover there is nothing we can do to prevent being blinded so you can't rationalize that the other guy is allowing it to occur.


I was once driving my friend's car at night - which had broken headlights such that only the brights worked - and I DID have a police officer do a u-turn and chase me when I failed to dim the lights. So yes, there actually is a punishment when you don't do it. He pulled me over and was pretty upset until the situation was explained and I proved that the lights didn't work except on the bright setting.

This may be an uncommon occurrence, but it is definitely a strong incentive for me to always dim my lights, apart from the safety and fairness aspects.


Dimming one's headlights to oncoming traffic (as well as when following another car closely) is the law in nearly all, if not all, 50 states.


#5 made a pretty good point about brights and weather conditions. A lot of people, at least in my experience, seem to not be aware that you can improve your visibility in heavy fog or snow (and maybe rain, I'm on the fence on that one) simply by having your dims on, because less light is reflected back at you.