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?


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  1. Tim Miller says:

    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…

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  2. Adam says:

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

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  3. Dim Bulb says:

    The Golden Rule.

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  4. Tim says:

    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.

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  5. Dim bulb in the distance. says:

    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.

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  6. chris markl says:

    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.

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  7. Alonso says:

    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.

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  8. PP says:

    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.

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